Assessment of the effect of Goukamma Marine Protected Area on community structure and fishery dynamics
- Authors: Götz, Albrecht
- Date: 2006
- Subjects: Goukamma Marine Protected Area Reef fishes -- South Africa Marine fishes -- South Africa Fishery management -- South Africa Marine resources conservation -- South Africa Marine parks and reserves -- South Africa Chrysoblephus laticeps Merluccius Argyrosomus
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5230 , http://hdl.handle.net/10962/d1005073
- Description: This study presents a detailed investigation into size, density and community structure of temperate marine reef fish in the medium-sized Goukamma Marine Protected Area (Goukamma MPA) and adjacent fishing grounds on the south coast of South Africa. The oceanographic conditions, the spatial distribution of the benthic community and the prevailing fishing effort are also described. Life history traits and per-recruit (PR) models for the principle target species, roman (Crysoblephus laticeps) are compared between the protected and exploited area. From the study results, various strategies are proposed for the use of MPAs in the conservation and management of linefish species along South Africa’s south coast. The distribution and topography of reefs in the protected and exploited sections of the study area were found to be comparable. Atmospheric pressure ranged from 992 to 1,032 mb, being significantly lower in summer. Wind speeds ranged from 0.7 to 71.3 km/h. Water temperatures ranged between 9.0 and 22.2 ºC and turbidity between 0.3 and 45.8 NTU. Water temperature and clarity were uniformly low in winter. In summer the water was generally warm, clear and stratified, with a thermocline at around 20 m, although intermittent upwelling events caused water temperature to decrease and clarity to deteriorate. Current speeds ranged between 0.11 and 2.59 km/h and were significantly higher in spring and autumn. Easterly currents prevailed in spring, summer and autumn and westerly and southerly currents in winter. Hake (Merluccius capensis), various resident reef fish and kob (Argyrosomus japonicus) were most frequently targeted by the local linefishery. A significant amount of illegal fishing was found to occur in the protected area. Fishing effort was found to be highest around the border of the MPA (2.7 boats/km²) and lowest in the core of the MPA (0.2 boats/km²). If law enforcement remains poor it may be necessary to adapt the management strategy to extend the reserve, thereby mitigating against illegal fishing and ensuring a core area of no exploitation. Various other alternatives were investigated and it was demonstrated that the amount of fish caught of legal size could be increased by about 23% and post-release mortality of undersized fish reduced by 50% through the introduction of a suit of restrictive measures. Randomly stratified underwater visual census (UVC) and controlled fishing were used to investigate the ichthyofauna and benthic community at protected and exploited sites in the study area. Resulting density and size data from 273 fishing sites and 177 point counts were analyzed using generalized linear models (GLMs). Fish communities were found to vary significantly, depending on the level of exploitation. Roman, the principle reef fish species targeted by the fishery had significantly higher densities within the protected parts of the study area (CPUE: 4.3 fish/anglerhour; UVC: 2.2 fish/point-count) as compared to the exploited part (CPUE: 3.4 fish/anglerhour; UVC: 1.8 fish/point-count), correlating strongly with the observed fishing effort. Also mean sizes were significantly higher in the protected area (299 mm from fishing survey and 233 mm from diving estimates) as compared to the exploited section (283 mm from fishing survey and 198 mm from diving estimates). Although other fish species also had significantly higher mean sizes at protected sites in most cases their densities were significantly lower. This suggests a top-down control of the fish community by the dominant predator (roman). The results of the UVC showed the diversity of the ichthyofauna to be significantly higher inside the protected area. Interestingly this did not apply to the results of the controlled fishing experiment where the diversity of fish in the catch was lower in the protected area - a result that may be explained by the selectivity of fishing for the most aggressive species – and a reminder of the limitations of controlled fishing experiments. Possibly the most important finding of the study revolved around the benthic community. These were significantly different at exploited and protected sites, with algae and crinoids more abundant at exploited sites. Crinoids are the principle food of roman and were low in abundance where roman abundances were high, suggesting that the dominant top predator reduced crinoids. Furthermore, it substantiates the correlation of roman abundance with fishing effort, since habitat preferences can be ruled out by the observed causal predator-prey distribution pattern. Low algae abundances at protected sites correlated with high strepie (Sarpa salpa) frequencies within the fish communities encountered there. Strepie, a shoaling and abundant benthic grazer, does not compete for food with roman, suggesting a high potential for coexistence of the two species. As expected, and found by other studies, life history traits of roman differed between protected and exploited sample-sites. With a significantly lower age-at-maturity and age-atsex- change, the exploited population showed a typical response to fishing effort. The sex ratio of this protogynous hermaphrodite was found to be sustained at healthy levels by phenotypic plasticity. However, one important additional factor was highlighted by the study; the average condition factor of the protected population was significantly lower (0.0283 g/cm³) compared to the exploited population (0.0295 g/cm³). This was probably due to the higher intra-specific competition for lower food abundance in the protected area. Interestingly the diving and fishing survey methods yielded similar mortality results for roman. Total mortality rate estimates derived from length frequency analysis from the diving and fishing survey were not different (0.32 and 0.29 y⁻¹, respectively) as were natural mortality rate estimates (0.24 and 0.19 y⁻¹, respectively). Natural mortality rate (M) estimates indicated by Pauly’s and Hoenig’s relationship were similar (0.25 and 0.23 y⁻¹, respectively). Detailed yield-per-recruit (Y/R) and spawner biomass-per-recruit (SB/R) analyses were presented for different levels of M, varying age-at-recruitment (tR) and fishing mortality (F). Current tR (7.60 y) and F (0.16 and 0.25 y⁻¹, from the diving and fishing dataset, respectively) suggests an optimal exploitation of the population in the exploited part of the study area. However, a separate SB/R analysis of the male part of the population showed their vulnerability to over-exploitation, even at reduced age-at-sex-change from fishing. There therefore remains a high risk of recruitment failure for the roman population. Of course MPAs can be used to measure stock status directly if the influence of factors such as cachability, habitat and sampling method on CPUE assessments can be limited or reduced. The experimental design in this study allowed for contemporary CPUE comparisons across the border of the Goukamma MPA. Results were similar to those obtained by the SB/R analyses. CPUE extrapolations therefore, using small MPAs, can provide reliable and consistent estimates, and offer a practical alternative to conventional assessment strategies. This study has highlighted the importance of ensuring a well structured and comprehensive survey design when undertaking a comparison of protected and exploited marine areas. The results provide a comprehensive framework for future management of the Goukamma MPA and other protected areas along the temperate coastline of South Africa.
- Full Text:
- Date Issued: 2006
- Authors: Götz, Albrecht
- Date: 2006
- Subjects: Goukamma Marine Protected Area Reef fishes -- South Africa Marine fishes -- South Africa Fishery management -- South Africa Marine resources conservation -- South Africa Marine parks and reserves -- South Africa Chrysoblephus laticeps Merluccius Argyrosomus
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5230 , http://hdl.handle.net/10962/d1005073
- Description: This study presents a detailed investigation into size, density and community structure of temperate marine reef fish in the medium-sized Goukamma Marine Protected Area (Goukamma MPA) and adjacent fishing grounds on the south coast of South Africa. The oceanographic conditions, the spatial distribution of the benthic community and the prevailing fishing effort are also described. Life history traits and per-recruit (PR) models for the principle target species, roman (Crysoblephus laticeps) are compared between the protected and exploited area. From the study results, various strategies are proposed for the use of MPAs in the conservation and management of linefish species along South Africa’s south coast. The distribution and topography of reefs in the protected and exploited sections of the study area were found to be comparable. Atmospheric pressure ranged from 992 to 1,032 mb, being significantly lower in summer. Wind speeds ranged from 0.7 to 71.3 km/h. Water temperatures ranged between 9.0 and 22.2 ºC and turbidity between 0.3 and 45.8 NTU. Water temperature and clarity were uniformly low in winter. In summer the water was generally warm, clear and stratified, with a thermocline at around 20 m, although intermittent upwelling events caused water temperature to decrease and clarity to deteriorate. Current speeds ranged between 0.11 and 2.59 km/h and were significantly higher in spring and autumn. Easterly currents prevailed in spring, summer and autumn and westerly and southerly currents in winter. Hake (Merluccius capensis), various resident reef fish and kob (Argyrosomus japonicus) were most frequently targeted by the local linefishery. A significant amount of illegal fishing was found to occur in the protected area. Fishing effort was found to be highest around the border of the MPA (2.7 boats/km²) and lowest in the core of the MPA (0.2 boats/km²). If law enforcement remains poor it may be necessary to adapt the management strategy to extend the reserve, thereby mitigating against illegal fishing and ensuring a core area of no exploitation. Various other alternatives were investigated and it was demonstrated that the amount of fish caught of legal size could be increased by about 23% and post-release mortality of undersized fish reduced by 50% through the introduction of a suit of restrictive measures. Randomly stratified underwater visual census (UVC) and controlled fishing were used to investigate the ichthyofauna and benthic community at protected and exploited sites in the study area. Resulting density and size data from 273 fishing sites and 177 point counts were analyzed using generalized linear models (GLMs). Fish communities were found to vary significantly, depending on the level of exploitation. Roman, the principle reef fish species targeted by the fishery had significantly higher densities within the protected parts of the study area (CPUE: 4.3 fish/anglerhour; UVC: 2.2 fish/point-count) as compared to the exploited part (CPUE: 3.4 fish/anglerhour; UVC: 1.8 fish/point-count), correlating strongly with the observed fishing effort. Also mean sizes were significantly higher in the protected area (299 mm from fishing survey and 233 mm from diving estimates) as compared to the exploited section (283 mm from fishing survey and 198 mm from diving estimates). Although other fish species also had significantly higher mean sizes at protected sites in most cases their densities were significantly lower. This suggests a top-down control of the fish community by the dominant predator (roman). The results of the UVC showed the diversity of the ichthyofauna to be significantly higher inside the protected area. Interestingly this did not apply to the results of the controlled fishing experiment where the diversity of fish in the catch was lower in the protected area - a result that may be explained by the selectivity of fishing for the most aggressive species – and a reminder of the limitations of controlled fishing experiments. Possibly the most important finding of the study revolved around the benthic community. These were significantly different at exploited and protected sites, with algae and crinoids more abundant at exploited sites. Crinoids are the principle food of roman and were low in abundance where roman abundances were high, suggesting that the dominant top predator reduced crinoids. Furthermore, it substantiates the correlation of roman abundance with fishing effort, since habitat preferences can be ruled out by the observed causal predator-prey distribution pattern. Low algae abundances at protected sites correlated with high strepie (Sarpa salpa) frequencies within the fish communities encountered there. Strepie, a shoaling and abundant benthic grazer, does not compete for food with roman, suggesting a high potential for coexistence of the two species. As expected, and found by other studies, life history traits of roman differed between protected and exploited sample-sites. With a significantly lower age-at-maturity and age-atsex- change, the exploited population showed a typical response to fishing effort. The sex ratio of this protogynous hermaphrodite was found to be sustained at healthy levels by phenotypic plasticity. However, one important additional factor was highlighted by the study; the average condition factor of the protected population was significantly lower (0.0283 g/cm³) compared to the exploited population (0.0295 g/cm³). This was probably due to the higher intra-specific competition for lower food abundance in the protected area. Interestingly the diving and fishing survey methods yielded similar mortality results for roman. Total mortality rate estimates derived from length frequency analysis from the diving and fishing survey were not different (0.32 and 0.29 y⁻¹, respectively) as were natural mortality rate estimates (0.24 and 0.19 y⁻¹, respectively). Natural mortality rate (M) estimates indicated by Pauly’s and Hoenig’s relationship were similar (0.25 and 0.23 y⁻¹, respectively). Detailed yield-per-recruit (Y/R) and spawner biomass-per-recruit (SB/R) analyses were presented for different levels of M, varying age-at-recruitment (tR) and fishing mortality (F). Current tR (7.60 y) and F (0.16 and 0.25 y⁻¹, from the diving and fishing dataset, respectively) suggests an optimal exploitation of the population in the exploited part of the study area. However, a separate SB/R analysis of the male part of the population showed their vulnerability to over-exploitation, even at reduced age-at-sex-change from fishing. There therefore remains a high risk of recruitment failure for the roman population. Of course MPAs can be used to measure stock status directly if the influence of factors such as cachability, habitat and sampling method on CPUE assessments can be limited or reduced. The experimental design in this study allowed for contemporary CPUE comparisons across the border of the Goukamma MPA. Results were similar to those obtained by the SB/R analyses. CPUE extrapolations therefore, using small MPAs, can provide reliable and consistent estimates, and offer a practical alternative to conventional assessment strategies. This study has highlighted the importance of ensuring a well structured and comprehensive survey design when undertaking a comparison of protected and exploited marine areas. The results provide a comprehensive framework for future management of the Goukamma MPA and other protected areas along the temperate coastline of South Africa.
- Full Text:
- Date Issued: 2006
Empirical studies of fish movement behaviour and their application in spatially explicit models for marine conservation
- Authors: Kerwath, Sven Ebo
- Date: 2006
- Subjects: Fishing -- South Africa Fishes -- Behavior -- South Africa Fish tagging Marine parks and reserves -- South Africa Marine resources conservation Pomadasys -- South Africa Reef fishes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5277 , http://hdl.handle.net/10962/d1005121
- Description: This thesis investigates the movement behaviour of South African two coastal fish species and evaluates the effectiveness of marine protected areas (MPAs) in their protection and management. Its primary focus is on resolving the movement patterns of roman Chrysoblephus laticeps (Sparidae) in and around the Goukamma and Castle Rock MPAs in the Western Cape province of South Africa. A pilot study of the methodology investigated the movement behaviour of spotted grunter Pomadasys commersonnii (Haemulidae) in the sheltered East Kleinmonde Estuary in the Eastern Cape province. The application of different tagging methods was tested in a controlled tank experiment. Tagged roman were monitored over a 198-day period. Barbed dart, t-bar anchor and Visible Implanted Fluorescent Elastomer (VIFE) tags were compared. Application techniques and underwater visibility of VIFE tags were tested on roman and on fransmadam Boobsoidia inornata in a pilot study. Needles of gauge 25 were found to be optimal for VIFE tag application. Whereas VIFE tagging caused fin rot in fransmadam, it had no negative effect on roman. VIFE tagged fish could be identified by divers from a distance of three metres under ambient light in an observation tank in five metres water depth. There was no significant difference in growth rate between groups of roman with different tags and controls after 198 days. High tag loss rates were experienced for barbed dart and t-bar anchor tags, although barbed dart tags performed better than t-bar anchor tags. Although some of the VIFE marks had deteriorated, all VIFE tagged fish were individually recognised at the end of the study. Conventional dart and VIFE tags are feasible methods to tag roman. However, the high tag loss rate of conventional tags must be taken into account in the design of a tagging study. Previous mark and recapture studies on roman are beset with a number of problems. Poor experimental design and low precision of capture positions resulted in equivocal results of limited value. A tagging experiment was designed to eliminate ambiguity in data interpretation and to produce a dataset that could be used to model roman residency and dispersal. A combination of conventional barbed dart tags and Visible Implanted Fluorescent Elastomer tags was used to tag roman in the Goukamma Marine Protected Area (GMPA) on the temperate South African south coast. Sixty one percent of roman were recaptured within 50 m of the tagging position. A small proportion moved considerable distances of up to four kilometres. The extent of these movements was not dependent on fish size or sex. Data from this experiment and from a previous tagging study in the Tsitsikamma National Park (TNP) were used to model the resident behaviour of roman. The model suggests a probability of 91% (GMPA) and 94% (TNP) of residency within a 10000 m² cell. This result suggests that individual roman will benefit from protection in small MPAs. A different experimental approach was required to investigate the exact home range of this species. Firstly the feasibility of using acoustic telemetry to study the movement of coastal fish in South Africa was investigated. The telemetry equipment comprised two VEMCO V8 transmitters and a VEMCO VR60 receiver linked to a directional hydrophone. A tank experiment was conducted to examine the effects of the transmitter implantation. A tracking experiment was conducted on spotted grunter Pomadasys commersonnii in the East Kleinmonde Estuary. Operated fish recovered quickly and, with respect to swimming behaviour and growth rates, no differences were found between fish with implants and controls. The maximum detection range in the estuary was 400 m. Interference between different transmitter frequencies was negligible. Transmitter location recordings were found to be accurate within five metres. Two fish were tracked over a seven-day period. The fish preferred the lower reaches of the estuary where they made repeated and prolonged use of specific areas. The success of the initial experiments allowed this method to be used to investigate the spatial utilisation and activity patterns of roman Chrysoblephus laticeps. Surgically implanted VEMCO V8, V13 and V16 transmitters were used to track 13 roman inside the Castle Rock MPA in False Bay. Transmitters implanted into C. laticeps in tanks had no apparent effects on growth and physiology. Manual boatand diver-based tracking experiments covered a 17-month period. A VEMCO VRAP radio acoustic positioning system was used over two one-month periods during and after the spawning season of roman. Analysis of data using a 95% fixed kernel algorithm suggests that roman are resident throughout their adult life, occupying home ranges between 1000 and 3000 m². Activity was lower at night. During periods of cold-water upwelling, fish retreated into caves. During the spawning season, females extended their home ranges, possibly to mate with different males. These results confirm that this species is well suited for protection and management with small MPAs. The effect of two MPAs on the South African south coast on the population of C. laticeps was simulated with a spatially explicit individual based model (IBM). Life history parameters determined in recent studies and the effect of fishing on the size of sex change was taken into account. Fish densities and size frequencies were based on recent underwater visual census. The distribution of suitable habitat in the study areas was also incorporated. The results show a rapid recovery of the fish size frequency spectrum and sex ratio to pre-exploitation levels inside both MPAs. Little 'spillover' of fish into the fished areas occurred resulting in negligible improvement of catches. The results suggest that for resident species like roman, even small MPAs offer sufficient protection.
- Full Text:
- Date Issued: 2006
- Authors: Kerwath, Sven Ebo
- Date: 2006
- Subjects: Fishing -- South Africa Fishes -- Behavior -- South Africa Fish tagging Marine parks and reserves -- South Africa Marine resources conservation Pomadasys -- South Africa Reef fishes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5277 , http://hdl.handle.net/10962/d1005121
- Description: This thesis investigates the movement behaviour of South African two coastal fish species and evaluates the effectiveness of marine protected areas (MPAs) in their protection and management. Its primary focus is on resolving the movement patterns of roman Chrysoblephus laticeps (Sparidae) in and around the Goukamma and Castle Rock MPAs in the Western Cape province of South Africa. A pilot study of the methodology investigated the movement behaviour of spotted grunter Pomadasys commersonnii (Haemulidae) in the sheltered East Kleinmonde Estuary in the Eastern Cape province. The application of different tagging methods was tested in a controlled tank experiment. Tagged roman were monitored over a 198-day period. Barbed dart, t-bar anchor and Visible Implanted Fluorescent Elastomer (VIFE) tags were compared. Application techniques and underwater visibility of VIFE tags were tested on roman and on fransmadam Boobsoidia inornata in a pilot study. Needles of gauge 25 were found to be optimal for VIFE tag application. Whereas VIFE tagging caused fin rot in fransmadam, it had no negative effect on roman. VIFE tagged fish could be identified by divers from a distance of three metres under ambient light in an observation tank in five metres water depth. There was no significant difference in growth rate between groups of roman with different tags and controls after 198 days. High tag loss rates were experienced for barbed dart and t-bar anchor tags, although barbed dart tags performed better than t-bar anchor tags. Although some of the VIFE marks had deteriorated, all VIFE tagged fish were individually recognised at the end of the study. Conventional dart and VIFE tags are feasible methods to tag roman. However, the high tag loss rate of conventional tags must be taken into account in the design of a tagging study. Previous mark and recapture studies on roman are beset with a number of problems. Poor experimental design and low precision of capture positions resulted in equivocal results of limited value. A tagging experiment was designed to eliminate ambiguity in data interpretation and to produce a dataset that could be used to model roman residency and dispersal. A combination of conventional barbed dart tags and Visible Implanted Fluorescent Elastomer tags was used to tag roman in the Goukamma Marine Protected Area (GMPA) on the temperate South African south coast. Sixty one percent of roman were recaptured within 50 m of the tagging position. A small proportion moved considerable distances of up to four kilometres. The extent of these movements was not dependent on fish size or sex. Data from this experiment and from a previous tagging study in the Tsitsikamma National Park (TNP) were used to model the resident behaviour of roman. The model suggests a probability of 91% (GMPA) and 94% (TNP) of residency within a 10000 m² cell. This result suggests that individual roman will benefit from protection in small MPAs. A different experimental approach was required to investigate the exact home range of this species. Firstly the feasibility of using acoustic telemetry to study the movement of coastal fish in South Africa was investigated. The telemetry equipment comprised two VEMCO V8 transmitters and a VEMCO VR60 receiver linked to a directional hydrophone. A tank experiment was conducted to examine the effects of the transmitter implantation. A tracking experiment was conducted on spotted grunter Pomadasys commersonnii in the East Kleinmonde Estuary. Operated fish recovered quickly and, with respect to swimming behaviour and growth rates, no differences were found between fish with implants and controls. The maximum detection range in the estuary was 400 m. Interference between different transmitter frequencies was negligible. Transmitter location recordings were found to be accurate within five metres. Two fish were tracked over a seven-day period. The fish preferred the lower reaches of the estuary where they made repeated and prolonged use of specific areas. The success of the initial experiments allowed this method to be used to investigate the spatial utilisation and activity patterns of roman Chrysoblephus laticeps. Surgically implanted VEMCO V8, V13 and V16 transmitters were used to track 13 roman inside the Castle Rock MPA in False Bay. Transmitters implanted into C. laticeps in tanks had no apparent effects on growth and physiology. Manual boatand diver-based tracking experiments covered a 17-month period. A VEMCO VRAP radio acoustic positioning system was used over two one-month periods during and after the spawning season of roman. Analysis of data using a 95% fixed kernel algorithm suggests that roman are resident throughout their adult life, occupying home ranges between 1000 and 3000 m². Activity was lower at night. During periods of cold-water upwelling, fish retreated into caves. During the spawning season, females extended their home ranges, possibly to mate with different males. These results confirm that this species is well suited for protection and management with small MPAs. The effect of two MPAs on the South African south coast on the population of C. laticeps was simulated with a spatially explicit individual based model (IBM). Life history parameters determined in recent studies and the effect of fishing on the size of sex change was taken into account. Fish densities and size frequencies were based on recent underwater visual census. The distribution of suitable habitat in the study areas was also incorporated. The results show a rapid recovery of the fish size frequency spectrum and sex ratio to pre-exploitation levels inside both MPAs. Little 'spillover' of fish into the fished areas occurred resulting in negligible improvement of catches. The results suggest that for resident species like roman, even small MPAs offer sufficient protection.
- Full Text:
- Date Issued: 2006
Movement patterns of spotted grunter, Pomadasys commersonnii (Haemulidae), in a highly turbid South African estuary
- Authors: Childs, Amber-Robyn
- Date: 2006
- Subjects: Grunts (Fishes) -- South Africa -- Great Fish River , Pomadasys -- South Africa -- Great Fish River , Freshwater fishes -- South Africa -- Great Fish River , Fishes -- Behavior -- South Africa -- Great Fish River , Estuarine fishes -- South Africa -- Great Fish River , Estaurine ecology -- South Africa -- Great Fish River , Marine ecology -- South Africa -- Great Fish River
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5304 , http://hdl.handle.net/10962/d1005149 , Grunts (Fishes) -- South Africa -- Great Fish River , Pomadasys -- South Africa -- Great Fish River , Freshwater fishes -- South Africa -- Great Fish River , Fishes -- Behavior -- South Africa -- Great Fish River , Estuarine fishes -- South Africa -- Great Fish River , Estaurine ecology -- South Africa -- Great Fish River , Marine ecology -- South Africa -- Great Fish River
- Description: The principal objective of this thesis was to gain an understanding of the movement patterns of spotted grunter Pomadasys commersonnii, an estuarine-dependent fishery species, in the turbid, freshwater dominated Great Fish Estuary. Both manual and automated telemetry methods were used to monitor the movements of spotted grunter during two separate studies conducted in summer and spring 2003 and 2004. Acoustic transmitters were surgically implanted into twenty spotted grunter with lengths between 263 and 387 mm TL in the first study and twenty spotted grunter ranging between 362 and 698 mm TL in the second study. The specific objectives were to gain an understanding of (i) the time spent in the estuarine environment (ii) the space use and home range size, and (iii) the abiotic factors governing the movement patterns of spotted grunter in the estuary. The nursery function of estuarine environments was highlighted in this study as adolescent spotted grunter spent a significantly larger proportion of their time in the estuary than adult fish (p < 0.0001; R² = 0.62). The increased frequency of sea trips, with the onset of sexual maturity, provided testimony of the end of the estuarinedependent phase of their life-cycle. Although considered to be predominantly marine, the adult spotted grunter in the Great Fish Estuary utilised the estuary for considerable periods. Adults are thought to frequent estuaries to forage, seek shelter and to possibly rid themselves of parasites. During this study, the number of sea trips made by tagged fish ranged from 0 to 53, and the duration ranged from 6 hours to 28 days. The tidal phase and time of day had a significant effect (p < 0.05) on the sea trips undertaken by fish. Most tagged spotted grunter left the estuary during the night (84%) on the outgoing tide, and most returned in the evening (77%) during the incoming tide. Sea temperature (p < 0.0001; R² = 0.34), barometric pressure (p = 0.004; R² = 0.19) and wind (p = 0.01) had a significant effect on the number of spotted grunter recorded in the estuary. Spotted grunter were more prone to return to the estuary after high barometric pressure, when low sea temperatures (upwelling events) prevailed. There was a significant positive relationship between home range size and fish length (p = 0.004; R² = 0.20). Small spotted grunter (< 450 mm TL) appeared to be highly resident, with a small home range (mean size = 129 167 m²), that was generally confined to a single core area. Larger individuals (> 450 mm TL) occupied larger home ranges (mean size = 218 435 m²) with numerous core areas. The home ranges of small and large spotted grunter overlapped considerably yielding evidence of two high use areas, situated 1.2 km and 7 km from the mouth of the Great Fish Estuary. Tagged spotted grunter were located in a wide range of salinity, turbidity and temperature, but were found to avoid temperatures below 16 ºC. The daily change in environmental variables (salinity, temperature and turbidity) had a significant effect on the change in fish position in the estuary (p < 0.0001; R² = 0.38). The distribution of tagged spotted grunter, particularly the larger individuals, in the Great Fish Estuary was influenced by the tidal phase (p < 0.05); they moved upriver on the incoming tide and downriver on the outgoing tide. This study provides an understanding of the movement patterns of spotted grunter in the estuary and between the estuarine and marine environments. Consequently, it provides information that will assist in the design of a management plan to promote sustainability of this important fishery species. The techniques used and developed in this study also have direct application for further studies on other important estuarinedependent fishery species.
- Full Text:
- Date Issued: 2006
- Authors: Childs, Amber-Robyn
- Date: 2006
- Subjects: Grunts (Fishes) -- South Africa -- Great Fish River , Pomadasys -- South Africa -- Great Fish River , Freshwater fishes -- South Africa -- Great Fish River , Fishes -- Behavior -- South Africa -- Great Fish River , Estuarine fishes -- South Africa -- Great Fish River , Estaurine ecology -- South Africa -- Great Fish River , Marine ecology -- South Africa -- Great Fish River
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5304 , http://hdl.handle.net/10962/d1005149 , Grunts (Fishes) -- South Africa -- Great Fish River , Pomadasys -- South Africa -- Great Fish River , Freshwater fishes -- South Africa -- Great Fish River , Fishes -- Behavior -- South Africa -- Great Fish River , Estuarine fishes -- South Africa -- Great Fish River , Estaurine ecology -- South Africa -- Great Fish River , Marine ecology -- South Africa -- Great Fish River
- Description: The principal objective of this thesis was to gain an understanding of the movement patterns of spotted grunter Pomadasys commersonnii, an estuarine-dependent fishery species, in the turbid, freshwater dominated Great Fish Estuary. Both manual and automated telemetry methods were used to monitor the movements of spotted grunter during two separate studies conducted in summer and spring 2003 and 2004. Acoustic transmitters were surgically implanted into twenty spotted grunter with lengths between 263 and 387 mm TL in the first study and twenty spotted grunter ranging between 362 and 698 mm TL in the second study. The specific objectives were to gain an understanding of (i) the time spent in the estuarine environment (ii) the space use and home range size, and (iii) the abiotic factors governing the movement patterns of spotted grunter in the estuary. The nursery function of estuarine environments was highlighted in this study as adolescent spotted grunter spent a significantly larger proportion of their time in the estuary than adult fish (p < 0.0001; R² = 0.62). The increased frequency of sea trips, with the onset of sexual maturity, provided testimony of the end of the estuarinedependent phase of their life-cycle. Although considered to be predominantly marine, the adult spotted grunter in the Great Fish Estuary utilised the estuary for considerable periods. Adults are thought to frequent estuaries to forage, seek shelter and to possibly rid themselves of parasites. During this study, the number of sea trips made by tagged fish ranged from 0 to 53, and the duration ranged from 6 hours to 28 days. The tidal phase and time of day had a significant effect (p < 0.05) on the sea trips undertaken by fish. Most tagged spotted grunter left the estuary during the night (84%) on the outgoing tide, and most returned in the evening (77%) during the incoming tide. Sea temperature (p < 0.0001; R² = 0.34), barometric pressure (p = 0.004; R² = 0.19) and wind (p = 0.01) had a significant effect on the number of spotted grunter recorded in the estuary. Spotted grunter were more prone to return to the estuary after high barometric pressure, when low sea temperatures (upwelling events) prevailed. There was a significant positive relationship between home range size and fish length (p = 0.004; R² = 0.20). Small spotted grunter (< 450 mm TL) appeared to be highly resident, with a small home range (mean size = 129 167 m²), that was generally confined to a single core area. Larger individuals (> 450 mm TL) occupied larger home ranges (mean size = 218 435 m²) with numerous core areas. The home ranges of small and large spotted grunter overlapped considerably yielding evidence of two high use areas, situated 1.2 km and 7 km from the mouth of the Great Fish Estuary. Tagged spotted grunter were located in a wide range of salinity, turbidity and temperature, but were found to avoid temperatures below 16 ºC. The daily change in environmental variables (salinity, temperature and turbidity) had a significant effect on the change in fish position in the estuary (p < 0.0001; R² = 0.38). The distribution of tagged spotted grunter, particularly the larger individuals, in the Great Fish Estuary was influenced by the tidal phase (p < 0.05); they moved upriver on the incoming tide and downriver on the outgoing tide. This study provides an understanding of the movement patterns of spotted grunter in the estuary and between the estuarine and marine environments. Consequently, it provides information that will assist in the design of a management plan to promote sustainability of this important fishery species. The techniques used and developed in this study also have direct application for further studies on other important estuarinedependent fishery species.
- Full Text:
- Date Issued: 2006
Population dynamics of the raggedtooth shark (carcharias taurus) along the east coast of South Africa
- Authors: Dicken, Matthew Laurence
- Date: 2006
- Subjects: Sharks -- South Africa Shark fisheries -- South Africa Fish populations -- South Africa Sand tiger shark Fish tagging -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5310 , http://hdl.handle.net/10962/d1005155
- Description: This thesis develops the first open population model for any shark species worldwide using the Cormack-Jolly-Seber (CJS) model. In conjunction with a tagging study, five auxiliary studies were conducted to investigate stock structure, post-release mortality, tag shedding, and tag-reporting rates. The results from each of the studies were used to correct for any violations of the models assumptions to provide the first unbiased estimates of survival and abundance for the raggedtooth shark (Carcharias taurus) in South Africa. The C. taurus population exhibited complex stock structuring, by size and sex. Competitive shore anglers fished an estimated 37, 820 fishing days.year⁻¹ (95% C.I. = 28, 281 - 47, 359 days.year⁻¹) for sharks, and caught 1764 (95% C.I. = 321 – 3207) C. taurus. Although released alive, post-release mortality ranged from 3.85% for young-of-the-year sharks to 18.46% for adult sharks. Between 1984 and 2004, a total of 3471 C. taurus were tagged. In all, 302-tagged sharks (8.7%) were recaptured. Both juvenile (< 1.8 m TL) and adult sharks (> 1.8 m TL) displayed philopatric behaviour for specific parts of their ranges, including gestating and parturition areas. Significant differences were observed in the percentage of recaptures between the different tag types, tagging programs, individual taggers and capture methods used to tag sharks. The annual tag retention rate for juvenile sharks, 94.19% (95% C.I. = 80.68% - 100.00%) was significantly higher than for adult sharks, estimated at 29.00% (95% C.I. = 6.76% - 64.39%). Tag reporting rates, from fishermen varied both spatially and temporally from 0.28 (95% C.I. = 0.00 – 0.63) to 0.77 (95% C.I. = 0.56 – 0.97). Associated tag wound damage and biofouling growth indicated that B-type tags were a suitable tag type for use on C. taurus, whereas C-type tags were not. The CJS bias-adjusted estimate for juvenile survival was 0.456 (95% C.I. = 0.367 – 0.516) and for adult sharks, 0.865 (95% C.I. = 0.795 – 0.915). From 1984 to 2004 the mean bias-adjusted population size for juvenile sharks was estimated at 3506 (95% C.I. = 2433 – 4350) and for adult sharks, 5899 (95% C.I. = 7216 – 11904). Trends in abundance over the 20-year study period indicated a stable, healthy population.
- Full Text:
- Date Issued: 2006
- Authors: Dicken, Matthew Laurence
- Date: 2006
- Subjects: Sharks -- South Africa Shark fisheries -- South Africa Fish populations -- South Africa Sand tiger shark Fish tagging -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5310 , http://hdl.handle.net/10962/d1005155
- Description: This thesis develops the first open population model for any shark species worldwide using the Cormack-Jolly-Seber (CJS) model. In conjunction with a tagging study, five auxiliary studies were conducted to investigate stock structure, post-release mortality, tag shedding, and tag-reporting rates. The results from each of the studies were used to correct for any violations of the models assumptions to provide the first unbiased estimates of survival and abundance for the raggedtooth shark (Carcharias taurus) in South Africa. The C. taurus population exhibited complex stock structuring, by size and sex. Competitive shore anglers fished an estimated 37, 820 fishing days.year⁻¹ (95% C.I. = 28, 281 - 47, 359 days.year⁻¹) for sharks, and caught 1764 (95% C.I. = 321 – 3207) C. taurus. Although released alive, post-release mortality ranged from 3.85% for young-of-the-year sharks to 18.46% for adult sharks. Between 1984 and 2004, a total of 3471 C. taurus were tagged. In all, 302-tagged sharks (8.7%) were recaptured. Both juvenile (< 1.8 m TL) and adult sharks (> 1.8 m TL) displayed philopatric behaviour for specific parts of their ranges, including gestating and parturition areas. Significant differences were observed in the percentage of recaptures between the different tag types, tagging programs, individual taggers and capture methods used to tag sharks. The annual tag retention rate for juvenile sharks, 94.19% (95% C.I. = 80.68% - 100.00%) was significantly higher than for adult sharks, estimated at 29.00% (95% C.I. = 6.76% - 64.39%). Tag reporting rates, from fishermen varied both spatially and temporally from 0.28 (95% C.I. = 0.00 – 0.63) to 0.77 (95% C.I. = 0.56 – 0.97). Associated tag wound damage and biofouling growth indicated that B-type tags were a suitable tag type for use on C. taurus, whereas C-type tags were not. The CJS bias-adjusted estimate for juvenile survival was 0.456 (95% C.I. = 0.367 – 0.516) and for adult sharks, 0.865 (95% C.I. = 0.795 – 0.915). From 1984 to 2004 the mean bias-adjusted population size for juvenile sharks was estimated at 3506 (95% C.I. = 2433 – 4350) and for adult sharks, 5899 (95% C.I. = 7216 – 11904). Trends in abundance over the 20-year study period indicated a stable, healthy population.
- Full Text:
- Date Issued: 2006
The fisheries potential of Marcusenius pongolensis, Oreochromis mossambicus and Schilbe intermedius in Mnjoli dam, Swaziland
- Authors: Khumalo, Nokuthula
- Date: 2006
- Subjects: Mozambique tilapia , Marcusenius pongolensis , Schilbe intermedius , Fishes -- Swaziland , Fisheries -- Swaziland , Tilapia -- Swaziland
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5283 , http://hdl.handle.net/10962/d1005127 , Mozambique tilapia , Marcusenius pongolensis , Schilbe intermedius , Fishes -- Swaziland , Fisheries -- Swaziland , Tilapia -- Swaziland
- Description: This thesis investigates aspects of the diversity, abundance and biology of the fish species inhabiting Mnjoli Dam, an irrigation dam that is located in the rural lowveld region of Swaziland. Specific objectives for this thesis were: to determine the fish species present and select three principal species based on their abundance; to investigate the relative abundance and distribution of the three selected species; and to describe key population parameters, such as growth, maturity, reproductive seasonality and mortality. The three dominant species were selected on their fisheries potential. These were Marcusenius pongolensis, Oreochromis mossambicus and Schilbe intermedius. Marcusenius pongolensis was the most abundant species in terms of both catch per unit effort and mass. Catch rates were shown to vary according to habitat type. Age and growth parameters were obtained from sectioned otoliths. Marginal zone analysis showed that annulus formation occurred in winter for all three species. The maximum-recorded ages were 8, 6 and 8 for M. pongolensis, O. mossambicus and S. intermedius, respectively. Growth for the three species was best described by the three parameter von Bertalanffy growth model as Lt = 1.88.67(1- exp⁻¹·⁴⁸⁽t⁺°·⁶⁷⁾) mm FL for M. pongolensis; Lt = 226.83(1- exp⁻°·⁴⁽t⁺²·°²⁾) mm TL for O. mossambicus and Lt = 214.59(1- exp⁻°·⁶°⁽t⁺¹·²°⁾) mm FL for S. intermedius. Sexual maturity was estimated for male and female M. pongolensis at 134 mm FL and 119 mm FL, respectively. Oreochromis mossambicus matured at 239 mm TL and S. intermedius at 205 mm FL. Two spawning peaks for M. pongolensis and S. intermedius were observed, one at the onset of summer (November) and the second at the beginning of autumn (February-March). Oreochromis mossambicus also exhibited two spawning peaks, one in spring (September) and the second in autumn (February –March). Mean mortality rate (Z), estimated using catch curve analysis was 0.77 year⁻¹ for M. pongolensis, 0.49 year⁻¹ for O. mossambicus and 0.79 year⁻¹ for S. intermedius. Natural mortality was assumed to be equal to Z since there is no fishery activity at the dam. Size specific selectivity curves were developed for each species. Of all the mesh sizes used, the 44 mm mesh size net had the highest catch rates in terms of numbers for M. pongolensis and S. intermedius. The 75mm mesh caught the highest catch rates for O. mossambicus. . The 44mm and 75 mm meshes seem to be the most suitable mesh sizes for harvesting the candidate species. It is concluded that no commercial fishery should be established on the dam, yet a small subsistence fishery could be a possible option. Management options such as input controls, open and closed seasons and areas and minimum sizes are discussed.
- Full Text:
- Date Issued: 2006
- Authors: Khumalo, Nokuthula
- Date: 2006
- Subjects: Mozambique tilapia , Marcusenius pongolensis , Schilbe intermedius , Fishes -- Swaziland , Fisheries -- Swaziland , Tilapia -- Swaziland
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5283 , http://hdl.handle.net/10962/d1005127 , Mozambique tilapia , Marcusenius pongolensis , Schilbe intermedius , Fishes -- Swaziland , Fisheries -- Swaziland , Tilapia -- Swaziland
- Description: This thesis investigates aspects of the diversity, abundance and biology of the fish species inhabiting Mnjoli Dam, an irrigation dam that is located in the rural lowveld region of Swaziland. Specific objectives for this thesis were: to determine the fish species present and select three principal species based on their abundance; to investigate the relative abundance and distribution of the three selected species; and to describe key population parameters, such as growth, maturity, reproductive seasonality and mortality. The three dominant species were selected on their fisheries potential. These were Marcusenius pongolensis, Oreochromis mossambicus and Schilbe intermedius. Marcusenius pongolensis was the most abundant species in terms of both catch per unit effort and mass. Catch rates were shown to vary according to habitat type. Age and growth parameters were obtained from sectioned otoliths. Marginal zone analysis showed that annulus formation occurred in winter for all three species. The maximum-recorded ages were 8, 6 and 8 for M. pongolensis, O. mossambicus and S. intermedius, respectively. Growth for the three species was best described by the three parameter von Bertalanffy growth model as Lt = 1.88.67(1- exp⁻¹·⁴⁸⁽t⁺°·⁶⁷⁾) mm FL for M. pongolensis; Lt = 226.83(1- exp⁻°·⁴⁽t⁺²·°²⁾) mm TL for O. mossambicus and Lt = 214.59(1- exp⁻°·⁶°⁽t⁺¹·²°⁾) mm FL for S. intermedius. Sexual maturity was estimated for male and female M. pongolensis at 134 mm FL and 119 mm FL, respectively. Oreochromis mossambicus matured at 239 mm TL and S. intermedius at 205 mm FL. Two spawning peaks for M. pongolensis and S. intermedius were observed, one at the onset of summer (November) and the second at the beginning of autumn (February-March). Oreochromis mossambicus also exhibited two spawning peaks, one in spring (September) and the second in autumn (February –March). Mean mortality rate (Z), estimated using catch curve analysis was 0.77 year⁻¹ for M. pongolensis, 0.49 year⁻¹ for O. mossambicus and 0.79 year⁻¹ for S. intermedius. Natural mortality was assumed to be equal to Z since there is no fishery activity at the dam. Size specific selectivity curves were developed for each species. Of all the mesh sizes used, the 44 mm mesh size net had the highest catch rates in terms of numbers for M. pongolensis and S. intermedius. The 75mm mesh caught the highest catch rates for O. mossambicus. . The 44mm and 75 mm meshes seem to be the most suitable mesh sizes for harvesting the candidate species. It is concluded that no commercial fishery should be established on the dam, yet a small subsistence fishery could be a possible option. Management options such as input controls, open and closed seasons and areas and minimum sizes are discussed.
- Full Text:
- Date Issued: 2006
The ichthyofauna in a small temporarily open/closed Eastern Cape estuary, South Africa
- Authors: Lukey, James Robert
- Date: 2006
- Subjects: Estuarine fishes -- South Africa -- Eastern Cape , Marine fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Eastern Cape , Fishes -- Growth -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5287 , http://hdl.handle.net/10962/d1005131 , Estuarine fishes -- South Africa -- Eastern Cape , Marine fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Eastern Cape , Fishes -- Growth -- South Africa -- Eastern Cape
- Description: The ichthyofaunal community structure, population dynamics and movement patterns in the small temporarily open/closed (TOCE) Grant’s Valley estuary, situated along the Eastern Cape coastline, were investigated over the period May 2004 to April 2005. Community structure in the littoral zone was assessed, while growth of selected ichthyofaunal species was investigated using the MULTIFAN model. Population size was assessed using mark recapture models and movement within the estuary using the Hilborn (1990) model. Total ichthyofaunal densities and biomass within the littoral zone ranged between 0.31 to 21.45 fish m⁻² and 0.20 to 4.67 g wwt m⁻², with the highest values typically recorded during the summer. Results of the study indicated that the ichthyofaunal community structure within the estuary was closely linked to the mouth phase and the establishment of a link to the marine environment via overtopping events. In the absence of any link to the sea, the ichthyofaunal community was numerically dominated by estuarine resident species, mainly Gilchristella aestuaria and to a lesser extent, by the river goby, Glossogobius callidus which collectively comprised ca. 88% of all fish sampled. The establishment of the link to the marine environment contributed to an increased contribution of marine breeding species (e.g. Rhabdosargus holubi, Myxus capensis and Atherina breviceps) to the total ichthyofaunal abundances. In contrast, total ichthyofaunal biomass was almost always dominated by marine breeding species by virtue of their larger sizes. Results of hierarchical cluster analyses did not identify any spatial patterns in the ichthyofaunal community within the littoral zone. Results of MULTIFAN analysis indicated estuarine resident fish species bred over an extended period with peaks occurring in the summer months. Conversely, marine breeding fish were shown to recruit into the estuary following overtopping and breaching events. Results of the mark-recapture experiment indicated a population of ca. 12 000 (11 219 – 13 311) individuals greater than 50mm SL. Marine-breeding species (R. holubi, Monodactylus falciformis, and two mullet species) numerically dominated the ichthyofauna, possibly as a result of their effective use of overtopping events. The two mullet species, M. capensis and Liza richardsonii, and the Cape stumpnose, R. holubi moved extensively throughout the estuary, while the remaining species exhibited restricted movement patterns possibly due to the preference for refuge and foraging areas associated with reed beds. The observed movement patterns of individual fish species appeared to be associated with both foraging behaviour and habitat selection.
- Full Text:
- Date Issued: 2006
- Authors: Lukey, James Robert
- Date: 2006
- Subjects: Estuarine fishes -- South Africa -- Eastern Cape , Marine fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Eastern Cape , Fishes -- Growth -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5287 , http://hdl.handle.net/10962/d1005131 , Estuarine fishes -- South Africa -- Eastern Cape , Marine fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Eastern Cape , Fishes -- Growth -- South Africa -- Eastern Cape
- Description: The ichthyofaunal community structure, population dynamics and movement patterns in the small temporarily open/closed (TOCE) Grant’s Valley estuary, situated along the Eastern Cape coastline, were investigated over the period May 2004 to April 2005. Community structure in the littoral zone was assessed, while growth of selected ichthyofaunal species was investigated using the MULTIFAN model. Population size was assessed using mark recapture models and movement within the estuary using the Hilborn (1990) model. Total ichthyofaunal densities and biomass within the littoral zone ranged between 0.31 to 21.45 fish m⁻² and 0.20 to 4.67 g wwt m⁻², with the highest values typically recorded during the summer. Results of the study indicated that the ichthyofaunal community structure within the estuary was closely linked to the mouth phase and the establishment of a link to the marine environment via overtopping events. In the absence of any link to the sea, the ichthyofaunal community was numerically dominated by estuarine resident species, mainly Gilchristella aestuaria and to a lesser extent, by the river goby, Glossogobius callidus which collectively comprised ca. 88% of all fish sampled. The establishment of the link to the marine environment contributed to an increased contribution of marine breeding species (e.g. Rhabdosargus holubi, Myxus capensis and Atherina breviceps) to the total ichthyofaunal abundances. In contrast, total ichthyofaunal biomass was almost always dominated by marine breeding species by virtue of their larger sizes. Results of hierarchical cluster analyses did not identify any spatial patterns in the ichthyofaunal community within the littoral zone. Results of MULTIFAN analysis indicated estuarine resident fish species bred over an extended period with peaks occurring in the summer months. Conversely, marine breeding fish were shown to recruit into the estuary following overtopping and breaching events. Results of the mark-recapture experiment indicated a population of ca. 12 000 (11 219 – 13 311) individuals greater than 50mm SL. Marine-breeding species (R. holubi, Monodactylus falciformis, and two mullet species) numerically dominated the ichthyofauna, possibly as a result of their effective use of overtopping events. The two mullet species, M. capensis and Liza richardsonii, and the Cape stumpnose, R. holubi moved extensively throughout the estuary, while the remaining species exhibited restricted movement patterns possibly due to the preference for refuge and foraging areas associated with reed beds. The observed movement patterns of individual fish species appeared to be associated with both foraging behaviour and habitat selection.
- Full Text:
- Date Issued: 2006
Towards a new approach for coastal governance with an assessment of the Plettenberg Bay nearshore linefisheries
- Smith, Martin Kyle Stratford
- Authors: Smith, Martin Kyle Stratford
- Date: 2006
- Subjects: Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Reef fishes -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5327 , http://hdl.handle.net/10962/d1005173 , Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Reef fishes -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
- Description: Under the guidance of the new coastal management policies within South Africa this thesis advocates a more integrated, co-operative approach to local coastal management. The project aimed to acquire baseline information on the local nearshore fishery and resource state and to propose a set of indicators that could be incorporated into the new management strategy. To gather the required information the project was split into two parts: 1) An assessment of the local linefisheries and 2) A comparative study of the reef fish community structure between exploited and unexploited reefs. The local linefisheries were assessed through the use of launch records, commercial catch records, access point and boat based surveys. A questionnaire was used to gather data on catch and effort, fisher demographics, fisher attitudes towards and knowledge of the current management regulations, assess the efficacy of the fisheries inspectorate and highlight spatial areas of fishing pressure. A total of 252 interviews and catch inspections were conducted. Total effort for the ski-boat fishery estimated from the access point survey was 890 boat days.year⁻¹ or 3560 fisher days. year⁻¹ compared to 736 boat days.year⁻¹ or 2944 fisher days. year⁻¹ recorded in the launch records. Effort was seasonal with greater pressure occurring over the summer holiday period. Analysis of the catch showed that Merluccius capensis, Argyrozona argyrozona, Argyrosomus inodorus, Chrysoblephus laticeps and Atractoscion aequidens were the most frequently caught species. The overall CPUE was 3.00±5.54kg.fisher⁻¹.day⁻¹ or 4.71±4.117 fish.fisher⁻¹.day⁻¹. Estimated targeted CPUE was 0.91±0.67kg.fisher⁻¹.day⁻¹ or 0.97±0.77 fish.fisher⁻¹.day⁻¹ for C. laticeps, 8.47±8.57kg.fisher⁻¹.day⁻¹ or 1.24±1.16 fish.fisher⁻¹.day⁻¹ for A. aequidens and 2.05±3.78kg.fisher⁻¹.day⁻¹ or 1.10±1.80 fish.fisher⁻¹.day⁻¹ for A. inodorus. Issues identified included poor fisher knowledge regarding linefish regulations, the low occurrence of fishery inspections and a limited degree of noncompliance. Although most fishers supported the current linefish management regulations, when tested on the size limits, bag limits and closed seasons of their target species a high proportion of fishers did not know the regulations (recreational 64%, charter 53%, commercial 42%). Furthermore only 27% of fishers had had their catch inspected whilst fishing in Plettenberg Bay and the majority of these had only been inspected once. Just over half the interviewees (60%) indicated that fishing had deteriorated within Plettenberg Bay with fewer and smaller fish being caught. The most common causes cited for this decline were commercial and recreational overfishing respectively. Underwater point counts and experimental angling were used to rapidly assess the state of the reef fish resource in Plettenberg Bay through a comparative study of the community structure between two exploited sites in Plettenberg Bay and two protected sites within the Tsitsikamma National Park. Generalized linear modeling showed that relative density of certain species was significantly different between the protected reefs inside the TNP and those exploited reefs within Plettenberg Bay. Both P. rupestris and C. laticeps had greater densities within the protected area whilst Chisquared tests showed that the size frequency distributions were significantly different with larger size-classes and the maximum size of fish greater within the reserve. These trends were noted with both the underwater visual surveys and the experimental angling. Multi-dimensional scaling and cluster analysis showed that there was an overall difference in the community structure between the study sites. It is hypothesised that through removal of key reef species and larger individuals that fishing has directly and indirectly affected the overall community structure. Within a simple framework based on ecological, institutional and social sustainability domains along with the results of the study area, a set of indicators is proposed and the sustainability of the local fishery scored within a rapid assessment matrix. The socio-economic domain scored the highest (83%) whilst the institutional domain scored the lowest (8.3%) and the ecological domain scored 25%, giving a total sustainability score of 38.8%. The results of this matrix show that at present the local fishery is non-sustainable and in need of greater management. By synthesizing papers dealing with and based on the concepts involved in Integrated Coastal Management, a structured approach is proposed to developing and implementing more holistic local coastal governance. It is envisaged that the framework to implement such an approach should be through the development of a local Coastal Management Plan and a subsidiary Bay Management Plan. Although stakeholder participation and representation is an essential component in the development of these plans, it is recommended that the local municipality should be the lead agent and incorporate the plans into the local Integrated Development and Spatial Plans thereby gaining long term local government support.
- Full Text:
- Date Issued: 2006
- Authors: Smith, Martin Kyle Stratford
- Date: 2006
- Subjects: Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Reef fishes -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5327 , http://hdl.handle.net/10962/d1005173 , Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Reef fishes -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
- Description: Under the guidance of the new coastal management policies within South Africa this thesis advocates a more integrated, co-operative approach to local coastal management. The project aimed to acquire baseline information on the local nearshore fishery and resource state and to propose a set of indicators that could be incorporated into the new management strategy. To gather the required information the project was split into two parts: 1) An assessment of the local linefisheries and 2) A comparative study of the reef fish community structure between exploited and unexploited reefs. The local linefisheries were assessed through the use of launch records, commercial catch records, access point and boat based surveys. A questionnaire was used to gather data on catch and effort, fisher demographics, fisher attitudes towards and knowledge of the current management regulations, assess the efficacy of the fisheries inspectorate and highlight spatial areas of fishing pressure. A total of 252 interviews and catch inspections were conducted. Total effort for the ski-boat fishery estimated from the access point survey was 890 boat days.year⁻¹ or 3560 fisher days. year⁻¹ compared to 736 boat days.year⁻¹ or 2944 fisher days. year⁻¹ recorded in the launch records. Effort was seasonal with greater pressure occurring over the summer holiday period. Analysis of the catch showed that Merluccius capensis, Argyrozona argyrozona, Argyrosomus inodorus, Chrysoblephus laticeps and Atractoscion aequidens were the most frequently caught species. The overall CPUE was 3.00±5.54kg.fisher⁻¹.day⁻¹ or 4.71±4.117 fish.fisher⁻¹.day⁻¹. Estimated targeted CPUE was 0.91±0.67kg.fisher⁻¹.day⁻¹ or 0.97±0.77 fish.fisher⁻¹.day⁻¹ for C. laticeps, 8.47±8.57kg.fisher⁻¹.day⁻¹ or 1.24±1.16 fish.fisher⁻¹.day⁻¹ for A. aequidens and 2.05±3.78kg.fisher⁻¹.day⁻¹ or 1.10±1.80 fish.fisher⁻¹.day⁻¹ for A. inodorus. Issues identified included poor fisher knowledge regarding linefish regulations, the low occurrence of fishery inspections and a limited degree of noncompliance. Although most fishers supported the current linefish management regulations, when tested on the size limits, bag limits and closed seasons of their target species a high proportion of fishers did not know the regulations (recreational 64%, charter 53%, commercial 42%). Furthermore only 27% of fishers had had their catch inspected whilst fishing in Plettenberg Bay and the majority of these had only been inspected once. Just over half the interviewees (60%) indicated that fishing had deteriorated within Plettenberg Bay with fewer and smaller fish being caught. The most common causes cited for this decline were commercial and recreational overfishing respectively. Underwater point counts and experimental angling were used to rapidly assess the state of the reef fish resource in Plettenberg Bay through a comparative study of the community structure between two exploited sites in Plettenberg Bay and two protected sites within the Tsitsikamma National Park. Generalized linear modeling showed that relative density of certain species was significantly different between the protected reefs inside the TNP and those exploited reefs within Plettenberg Bay. Both P. rupestris and C. laticeps had greater densities within the protected area whilst Chisquared tests showed that the size frequency distributions were significantly different with larger size-classes and the maximum size of fish greater within the reserve. These trends were noted with both the underwater visual surveys and the experimental angling. Multi-dimensional scaling and cluster analysis showed that there was an overall difference in the community structure between the study sites. It is hypothesised that through removal of key reef species and larger individuals that fishing has directly and indirectly affected the overall community structure. Within a simple framework based on ecological, institutional and social sustainability domains along with the results of the study area, a set of indicators is proposed and the sustainability of the local fishery scored within a rapid assessment matrix. The socio-economic domain scored the highest (83%) whilst the institutional domain scored the lowest (8.3%) and the ecological domain scored 25%, giving a total sustainability score of 38.8%. The results of this matrix show that at present the local fishery is non-sustainable and in need of greater management. By synthesizing papers dealing with and based on the concepts involved in Integrated Coastal Management, a structured approach is proposed to developing and implementing more holistic local coastal governance. It is envisaged that the framework to implement such an approach should be through the development of a local Coastal Management Plan and a subsidiary Bay Management Plan. Although stakeholder participation and representation is an essential component in the development of these plans, it is recommended that the local municipality should be the lead agent and incorporate the plans into the local Integrated Development and Spatial Plans thereby gaining long term local government support.
- Full Text:
- Date Issued: 2006
Towards a new approach for coastal governance with an assessment of the Plettenberg Bay shore-based linefishery
- Authors: King, Claire Margaret
- Date: 2006
- Subjects: Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5326 , http://hdl.handle.net/10962/d1005172 , Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
- Description: The overall aim of this thesis, as required by the funders, was to provide research that would contribute towards the development of a bay management plan, specifically information on the local fisheries. The thesis therefore includes an assessment of the local shore-based linefishery in terms of catch and effort and socio-economics, and the development of indicators from this information with which to assess the sustainability of the fishery. Finally an implementation strategy for an integrated coastal management approach for local resource governance is proposed The shore-based linefishery of Plettenberg Bay was assessed through a combination of roving creel and access point surveys which included questions aimed at the quantification of total effort, total catch and cpue, as well as the spatial trends in catch and effort. Angler demographics as well as opinions and knowledge of current fisheries regulations were obtained and the efficiency of the fishery inspectorate was assessed. The survey period extended from August 2003 to September 2004 during which 1189 angler interviews were conducted. Catch data obtained during this study was compared to catch data gathered during a research tagging program conducted in an area closed to fishing (Tsitsikamma National Park) and a semi-open area (Rebelsrus – Cape St. Francis), thereby highlighting differences in species composition, abundance and size distribution of certain species between areas of differing fishing pressures. The fishery surveys revealed that the shore-based fishery is primarily recreational (99%) and dominated by white males. Most anglers agreed with the current fisheries regulations (60%) and admitted to abiding by them, however when tested on the regulations of their target species, their knowledge was poor. Effort in the fishery was highly seasonal with peaks coinciding with major school holidays. Total annual effort was estimated at 102 566 angler-hours, with distinct spatial patterns in effort. Total annual catch for the Plettenberg Bay shore-based linefishery was estimated at 31 217 fish.year⁻¹ with a total mass of 13.6 tons. Thirty-six fish species (26 teleost species and 10 elasmobranchs species) were identified during the survey period with Blacktail Diplodus capensis, Strepie Sarpa salpa, Red tjor-tjor Pagellus natalensis, Shad Pomatomus saltatrix and Sand steenbras Lithognathus mormyrus being the five most commonly caught species. Only 32% of interviewed anglers were successful in catching a fish with just 22% catching their primary target species. In addition, a large proportion of the anglers (69%) reported a decline in catch rate, with most blaming the commercial sector as a reason for the decline. The overall catch rate was (cpue) 0.374 fish.angler.hour⁻¹ or 170 grams.angler.hour⁻¹, considerably lower than that obtained from the fishery exempt area (TNP = 1. 02 fish.angler.hour⁻¹) and the partially exploited area (Rebelsrus = 0.91 fish.angler.hour⁻¹). In terms of species composition the most obvious difference between the three areas was the low proportion of non-migratory reef-associated species like red roman, poenskop, John brown, santer and bronze bream in Plettenberg Bay. Size comparisons revealed that the majority of species (particularly reef-associated species) were larger in the TNP than both the semi-exploited (Rebelsrus) and exploited area (Plettenberg Bay). Collectively theses findings suggest that certain species have been locally depleted, that recreational fishing has impacted heavily on the fish stocks and that even partial closure or limited access to an area can offer protection. From the results key issues were identified and sustainability indicators proposed according to the three sustainability domains (ecological, institutional and social) proposed by Pajak (2000). Within the ecological domain the most pertinent issue was the low catch rate, particularly for reef-associated species. Indicators to track these issues included: percentage of successful trips (where fish were caught), percentage of anglers that reached their daily bag limits and the proportion of the overall catch that comprised larger, more desirable species. Institutionally the most pertinent issue was the apparent inability of management institutions to manage effectively marine resources within Plettenberg Bay. Indicators within this domain included the proportion of anglers who were inspected, the existence of a localised management plan and an associated monitoring programme. Socially the fishery proved to be fairly sustainable. Indicators included in this domain were the proportion of subsistence anglers in the local fishing community, the percentage of correct answers pertaining to current fishery regulations, the level of noncompliance and the percentage of undersize fish retained. Aggregation of all the indicators within a sustainability matrix revealed that the Plettenberg Bay shore-based linefishery was unsustainable and thus requires increased local management effort. Since there is no local management strategy in place, an integrated coastal management approach for the governance of the coastal resources in Plettenberg Bay has been proposed. The development of a Coastal Management Plan and a subsidiary Bay Management Plan provide the frameworks within which management strategies can be put into operation.
- Full Text:
- Date Issued: 2006
- Authors: King, Claire Margaret
- Date: 2006
- Subjects: Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5326 , http://hdl.handle.net/10962/d1005172 , Fishery management -- South Africa -- Plettenberg Bay , Fisheries -- South Africa -- Plettenberg Bay , Coastal zone management -- South Africa -- Plettenberg Bay
- Description: The overall aim of this thesis, as required by the funders, was to provide research that would contribute towards the development of a bay management plan, specifically information on the local fisheries. The thesis therefore includes an assessment of the local shore-based linefishery in terms of catch and effort and socio-economics, and the development of indicators from this information with which to assess the sustainability of the fishery. Finally an implementation strategy for an integrated coastal management approach for local resource governance is proposed The shore-based linefishery of Plettenberg Bay was assessed through a combination of roving creel and access point surveys which included questions aimed at the quantification of total effort, total catch and cpue, as well as the spatial trends in catch and effort. Angler demographics as well as opinions and knowledge of current fisheries regulations were obtained and the efficiency of the fishery inspectorate was assessed. The survey period extended from August 2003 to September 2004 during which 1189 angler interviews were conducted. Catch data obtained during this study was compared to catch data gathered during a research tagging program conducted in an area closed to fishing (Tsitsikamma National Park) and a semi-open area (Rebelsrus – Cape St. Francis), thereby highlighting differences in species composition, abundance and size distribution of certain species between areas of differing fishing pressures. The fishery surveys revealed that the shore-based fishery is primarily recreational (99%) and dominated by white males. Most anglers agreed with the current fisheries regulations (60%) and admitted to abiding by them, however when tested on the regulations of their target species, their knowledge was poor. Effort in the fishery was highly seasonal with peaks coinciding with major school holidays. Total annual effort was estimated at 102 566 angler-hours, with distinct spatial patterns in effort. Total annual catch for the Plettenberg Bay shore-based linefishery was estimated at 31 217 fish.year⁻¹ with a total mass of 13.6 tons. Thirty-six fish species (26 teleost species and 10 elasmobranchs species) were identified during the survey period with Blacktail Diplodus capensis, Strepie Sarpa salpa, Red tjor-tjor Pagellus natalensis, Shad Pomatomus saltatrix and Sand steenbras Lithognathus mormyrus being the five most commonly caught species. Only 32% of interviewed anglers were successful in catching a fish with just 22% catching their primary target species. In addition, a large proportion of the anglers (69%) reported a decline in catch rate, with most blaming the commercial sector as a reason for the decline. The overall catch rate was (cpue) 0.374 fish.angler.hour⁻¹ or 170 grams.angler.hour⁻¹, considerably lower than that obtained from the fishery exempt area (TNP = 1. 02 fish.angler.hour⁻¹) and the partially exploited area (Rebelsrus = 0.91 fish.angler.hour⁻¹). In terms of species composition the most obvious difference between the three areas was the low proportion of non-migratory reef-associated species like red roman, poenskop, John brown, santer and bronze bream in Plettenberg Bay. Size comparisons revealed that the majority of species (particularly reef-associated species) were larger in the TNP than both the semi-exploited (Rebelsrus) and exploited area (Plettenberg Bay). Collectively theses findings suggest that certain species have been locally depleted, that recreational fishing has impacted heavily on the fish stocks and that even partial closure or limited access to an area can offer protection. From the results key issues were identified and sustainability indicators proposed according to the three sustainability domains (ecological, institutional and social) proposed by Pajak (2000). Within the ecological domain the most pertinent issue was the low catch rate, particularly for reef-associated species. Indicators to track these issues included: percentage of successful trips (where fish were caught), percentage of anglers that reached their daily bag limits and the proportion of the overall catch that comprised larger, more desirable species. Institutionally the most pertinent issue was the apparent inability of management institutions to manage effectively marine resources within Plettenberg Bay. Indicators within this domain included the proportion of anglers who were inspected, the existence of a localised management plan and an associated monitoring programme. Socially the fishery proved to be fairly sustainable. Indicators included in this domain were the proportion of subsistence anglers in the local fishing community, the percentage of correct answers pertaining to current fishery regulations, the level of noncompliance and the percentage of undersize fish retained. Aggregation of all the indicators within a sustainability matrix revealed that the Plettenberg Bay shore-based linefishery was unsustainable and thus requires increased local management effort. Since there is no local management strategy in place, an integrated coastal management approach for the governance of the coastal resources in Plettenberg Bay has been proposed. The development of a Coastal Management Plan and a subsidiary Bay Management Plan provide the frameworks within which management strategies can be put into operation.
- Full Text:
- Date Issued: 2006
An assessment of the shore baitfishery in the Eastern Cape
- Authors: Mackenzie, Bernard Louis
- Date: 2005
- Subjects: Fishing baits -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fisheries -- South Africa -- Eastern Cape , Fishery -- Law and legislation -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5232 , http://hdl.handle.net/10962/d1005075 , Fishing baits -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fisheries -- South Africa -- Eastern Cape , Fishery -- Law and legislation -- South Africa
- Description: The collection of bait organisms goes hand-in-hand with shore-angling in South Africa, hence the level of bait-collection can be used as an indicator of fishing effort and vice versa. This emphasises the importance of understanding the fisheries for bait organisms. In 1998 the South African fisheries policy was revised, culminating in the Marine Living Resources Act No. 18 (1998) which supported sustainable development, equitable access to resources and stability of the industry. The policy also dealt with the needs of subsistence fishers who had previously been all but ignored. This study looks to continue in this direction by investigating the opportunities for the establishment and management implications of small-scale commercial baitfisheries in the Eastern Cape. Data were collected from eight clearly demarcated sampling areas using the roving survey method. A total of 97 survey trips were undertaken between September 2001 and April 2003 and 469 interviews were conducted on individual anglers. The data was analysed and discussed on the basis of three wider study regions and this allowed for a more accurate and focussed assessment of the fishery area and the potential for its formalisation. Recreational fishers (91.5%) dominated in each of the three regions surveyed. The low number of subsistence fishers encountered in this study is not a standard pattern throughout South Africa. The dominance of local residents in the shore-fishery could have an important impact on the success of a formalised baitfishery in that the greater proportion of the potential market is accessible throughout the year. Most recreational shore-anglers were middle-aged (43.8 years ± 12.9 years), and hence at the peak of their earning years and this may contribute towards the potential success of a small-scale commercial baitfishery. Most anglers and baitfishers were of the opinion that all South Africans owned and were responsible for managing the living marine resources. The vast majority of recreational users paid for and were in possession of valid permits and approved of the baitfishery regulations. This implies that the greater majority of users recognise that the state is the rightful custodian of the resource and is responsible for management. No subsistence users were in possession of permits. Resource users in the Gamtoos to Tsitsikamma National Park region, where the inspection rate was highest, had the best knowledge of the regulations regarding both baitfishing (67.2% ± 38.8%) and angling (79.8 ± 21.4%). This substantiates the hypothesis that there is a direct correlation between knowledge of the regulations and the rate of inspection. About 475 000 angler-days/year were fished in the study area, with the highest number of angler-days recorded in or near urban and peri-urban areas. Bronze bream (65.9%) and dusky kob (61.1%) were the two most commonly targeted species, followed by white steenbras (31.7%), white musselcracker (31.4%) and blacktail (20.2%). A total of four purchased and 19 collected bait species was recorded during the study. Sardine, chokka and pink prawn were the most frequently encountered purchased bait. Red bait, sand prawn, mullet, siffie, sand mussel, bloodworm and saddleback were the most frequently encountered collected bait species. Sand prawn was identified as the preferred bait species for a wide range of angling species. The total quantity of bait organisms used per fishing trip was markedly less than the total amount collected per trip. The ban of off-road vehicles (ORV's) from beaches (20 January 2002) resulted in spatial shifts in angler effort in certain areas, suggesting that total effort has reduced in areas where ORV's were commonly used. Subsequent to the ban, fishers were encountered, on average, much closer to access points. The value of small-scale baitfisheries within the total study area was estimated at about R7 million per year. Across the entire study area red bait was identified as the most valuable bait in the rock-and-surf fishery in monetary terms, while sand prawn was also important. The findings led to the conclusion that small-scale commercial baitfisheries in the study area are potentially viable. Scenarios for the establishment of baitfisheries are suggested and discussed.
- Full Text:
- Date Issued: 2005
- Authors: Mackenzie, Bernard Louis
- Date: 2005
- Subjects: Fishing baits -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fisheries -- South Africa -- Eastern Cape , Fishery -- Law and legislation -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5232 , http://hdl.handle.net/10962/d1005075 , Fishing baits -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fisheries -- South Africa -- Eastern Cape , Fishery -- Law and legislation -- South Africa
- Description: The collection of bait organisms goes hand-in-hand with shore-angling in South Africa, hence the level of bait-collection can be used as an indicator of fishing effort and vice versa. This emphasises the importance of understanding the fisheries for bait organisms. In 1998 the South African fisheries policy was revised, culminating in the Marine Living Resources Act No. 18 (1998) which supported sustainable development, equitable access to resources and stability of the industry. The policy also dealt with the needs of subsistence fishers who had previously been all but ignored. This study looks to continue in this direction by investigating the opportunities for the establishment and management implications of small-scale commercial baitfisheries in the Eastern Cape. Data were collected from eight clearly demarcated sampling areas using the roving survey method. A total of 97 survey trips were undertaken between September 2001 and April 2003 and 469 interviews were conducted on individual anglers. The data was analysed and discussed on the basis of three wider study regions and this allowed for a more accurate and focussed assessment of the fishery area and the potential for its formalisation. Recreational fishers (91.5%) dominated in each of the three regions surveyed. The low number of subsistence fishers encountered in this study is not a standard pattern throughout South Africa. The dominance of local residents in the shore-fishery could have an important impact on the success of a formalised baitfishery in that the greater proportion of the potential market is accessible throughout the year. Most recreational shore-anglers were middle-aged (43.8 years ± 12.9 years), and hence at the peak of their earning years and this may contribute towards the potential success of a small-scale commercial baitfishery. Most anglers and baitfishers were of the opinion that all South Africans owned and were responsible for managing the living marine resources. The vast majority of recreational users paid for and were in possession of valid permits and approved of the baitfishery regulations. This implies that the greater majority of users recognise that the state is the rightful custodian of the resource and is responsible for management. No subsistence users were in possession of permits. Resource users in the Gamtoos to Tsitsikamma National Park region, where the inspection rate was highest, had the best knowledge of the regulations regarding both baitfishing (67.2% ± 38.8%) and angling (79.8 ± 21.4%). This substantiates the hypothesis that there is a direct correlation between knowledge of the regulations and the rate of inspection. About 475 000 angler-days/year were fished in the study area, with the highest number of angler-days recorded in or near urban and peri-urban areas. Bronze bream (65.9%) and dusky kob (61.1%) were the two most commonly targeted species, followed by white steenbras (31.7%), white musselcracker (31.4%) and blacktail (20.2%). A total of four purchased and 19 collected bait species was recorded during the study. Sardine, chokka and pink prawn were the most frequently encountered purchased bait. Red bait, sand prawn, mullet, siffie, sand mussel, bloodworm and saddleback were the most frequently encountered collected bait species. Sand prawn was identified as the preferred bait species for a wide range of angling species. The total quantity of bait organisms used per fishing trip was markedly less than the total amount collected per trip. The ban of off-road vehicles (ORV's) from beaches (20 January 2002) resulted in spatial shifts in angler effort in certain areas, suggesting that total effort has reduced in areas where ORV's were commonly used. Subsequent to the ban, fishers were encountered, on average, much closer to access points. The value of small-scale baitfisheries within the total study area was estimated at about R7 million per year. Across the entire study area red bait was identified as the most valuable bait in the rock-and-surf fishery in monetary terms, while sand prawn was also important. The findings led to the conclusion that small-scale commercial baitfisheries in the study area are potentially viable. Scenarios for the establishment of baitfisheries are suggested and discussed.
- Full Text:
- Date Issued: 2005
Aspects of the ecology and management of the Soupfin shark (Galeorhinus galeus) in South Africa
- Authors: McCord, Meaghen Erica
- Date: 2005
- Subjects: Soupfin shark -- South Africa , Soupfin shark -- Ecology -- South Africa , Fishery management -- South Africa , Shark fisheries -- Management -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5223 , http://hdl.handle.net/10962/d1005066 , Soupfin shark -- South Africa , Soupfin shark -- Ecology -- South Africa , Fishery management -- South Africa , Shark fisheries -- Management -- South Africa
- Description: Global trends in teleost fisheries indicate significant population declines. Thus, alternative fisheries are being developed to meet the growing economic and nutritional demands of the expanding human population. Recently, it has been established that elasmobranch fisheries may fulfill these demands. As many elasmobranchs possess life-history characteristics that make them particularly vulnerable to overfishing, it is imperative to develop management strategies prior to the inception of these fisheries to ensure sustainable resource utilisation. In South Africa, elasmobranchs have been commercially exploited since the 1930s. Although generally considered an under-exploited resource, the potential for growth within these fisheries has been recognized. In 2005, the commercial shark fishery will undergo a transition from medium to long-term rights allocations. This represents an ideal opportunity for scientists and managers to develop precautionary species-specific management plans for commercially exploitable elasmobranch species. The soupfin shark (Galeorhinus galeus) is one of the principal target species in South Africa’s shark fisheries. Given its inherent susceptibility to overexploitation, G. galeus was selected as a management priority by South Africa’s regional fisheries organisation. The purpose of this study was to examine and describe the stock status of G. galeus in South Africa, and to develop a precautionary fishery management plan to ensure the sustainability of this resource. Age, growth, and mortality calculations for G. galeus were made from research survey data collected between 1996 and 1999. A small sample size precluded independent analyses of females. The maximum recorded age for G. galeus was 33 years. Estimated von Bertalanffy growth parameters from observed length-at-age for males and combined sexes were: L∞ 1542.8 mm TL, K 0.21 year⁻¹ , t₀ -2.79 year⁻¹ and L∞ 1560.3 mm TL, K 0.19 year¹, t₀ -3.03 year⁻¹, respectively. The age-at-50% maturity was determined to be 6 years, corresponding to 1011 mm TL for males and 1100 mm TL for combined sexes. Natural mortality was calculated as 0.126 yr⁻¹. The rate of instantaneous total mortality was calculated as 0.27 yr⁻¹. Catch trend analysis showed that catches and CPUE of G. galeus are increasing in the demersal longline fishery, and decreasing in the handline fishery. Decreasing catches and CPUE were observed in fishery-independent research survey data. The status of the soupfin shark stock was modelled using per-recruit analysis. The SB/R model indicated the soupfin shark is being optimally exploited and spawner biomass is at 43% of preexploitation levels. Current fishing levels ( F = 0.14 yr⁻¹) approximate the Fsb₄₀ level (F = 0.17 yr¹); thus, an increase in fishing pressure may lead to stock collapse. It was determined that the current age-at-capture (7.9 years) should be increased to 10 years, or 1420 mm TL, to maximize yield and minimize the possibility of recruitment failure. The results of this study indicate a need for immediate scientific and management intervention in South Africa’s soupfin shark fishery. An assessment report and fishery management plan for G. galeus was compiled, and several management options were proposed. These include the implementation of licence and size restrictions, as well as seasonal/area closures. The potential for an experimental gillnet fishery should be investigated.
- Full Text:
- Date Issued: 2005
- Authors: McCord, Meaghen Erica
- Date: 2005
- Subjects: Soupfin shark -- South Africa , Soupfin shark -- Ecology -- South Africa , Fishery management -- South Africa , Shark fisheries -- Management -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5223 , http://hdl.handle.net/10962/d1005066 , Soupfin shark -- South Africa , Soupfin shark -- Ecology -- South Africa , Fishery management -- South Africa , Shark fisheries -- Management -- South Africa
- Description: Global trends in teleost fisheries indicate significant population declines. Thus, alternative fisheries are being developed to meet the growing economic and nutritional demands of the expanding human population. Recently, it has been established that elasmobranch fisheries may fulfill these demands. As many elasmobranchs possess life-history characteristics that make them particularly vulnerable to overfishing, it is imperative to develop management strategies prior to the inception of these fisheries to ensure sustainable resource utilisation. In South Africa, elasmobranchs have been commercially exploited since the 1930s. Although generally considered an under-exploited resource, the potential for growth within these fisheries has been recognized. In 2005, the commercial shark fishery will undergo a transition from medium to long-term rights allocations. This represents an ideal opportunity for scientists and managers to develop precautionary species-specific management plans for commercially exploitable elasmobranch species. The soupfin shark (Galeorhinus galeus) is one of the principal target species in South Africa’s shark fisheries. Given its inherent susceptibility to overexploitation, G. galeus was selected as a management priority by South Africa’s regional fisheries organisation. The purpose of this study was to examine and describe the stock status of G. galeus in South Africa, and to develop a precautionary fishery management plan to ensure the sustainability of this resource. Age, growth, and mortality calculations for G. galeus were made from research survey data collected between 1996 and 1999. A small sample size precluded independent analyses of females. The maximum recorded age for G. galeus was 33 years. Estimated von Bertalanffy growth parameters from observed length-at-age for males and combined sexes were: L∞ 1542.8 mm TL, K 0.21 year⁻¹ , t₀ -2.79 year⁻¹ and L∞ 1560.3 mm TL, K 0.19 year¹, t₀ -3.03 year⁻¹, respectively. The age-at-50% maturity was determined to be 6 years, corresponding to 1011 mm TL for males and 1100 mm TL for combined sexes. Natural mortality was calculated as 0.126 yr⁻¹. The rate of instantaneous total mortality was calculated as 0.27 yr⁻¹. Catch trend analysis showed that catches and CPUE of G. galeus are increasing in the demersal longline fishery, and decreasing in the handline fishery. Decreasing catches and CPUE were observed in fishery-independent research survey data. The status of the soupfin shark stock was modelled using per-recruit analysis. The SB/R model indicated the soupfin shark is being optimally exploited and spawner biomass is at 43% of preexploitation levels. Current fishing levels ( F = 0.14 yr⁻¹) approximate the Fsb₄₀ level (F = 0.17 yr¹); thus, an increase in fishing pressure may lead to stock collapse. It was determined that the current age-at-capture (7.9 years) should be increased to 10 years, or 1420 mm TL, to maximize yield and minimize the possibility of recruitment failure. The results of this study indicate a need for immediate scientific and management intervention in South Africa’s soupfin shark fishery. An assessment report and fishery management plan for G. galeus was compiled, and several management options were proposed. These include the implementation of licence and size restrictions, as well as seasonal/area closures. The potential for an experimental gillnet fishery should be investigated.
- Full Text:
- Date Issued: 2005
Biology, population dynamics and management of carpenter (Argyrozona argyrozona) an endemic South African reef fish
- Authors: Brouwer, Stephen Leonard
- Date: 2005
- Subjects: Reef fishes -- South Africa Sparidae -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5241 , http://hdl.handle.net/10962/d1005084
- Description: Carpenter, Argyrozona argyrozona (Valenciennes, 1830), is an endemic South African sparid fish. They form an important component of the commercial linefishery on the South African east coast, where they are the third most important species landed. Recent investigations revealed that the catch per unit effort (cpue) of this species has declined markedly since the early 1900’s. Despite these declines and the importance of this resource, remarkably little biological information on this species exists for providing management advice. This thesis investigates the life history of carpenter, particularly those aspects that are used for management. This includes an investigation into the stock distribution and identification of nursery areas, and an assessment of age, growth, reproduction and movement patterns. Age and growth was assessed using methods based on both otoliths and mark-recapture. Transverse sagittal sections from the Tsitsikamma National Park showed clear opaque and translucent growth increments. Marginal growth zone analysis and mark-recapture of chemically tagged fish (Oxytetracycline) revealed that these were deposited on an annual basis: opaque in summer and translucent in winter. A. argyrozona were found to be long lived (up to 27 years) and slow growing. Within reader (between counts) and between readers average percent error (APE) was 5.3 and 1.8, respectively, showing that readability of carpenter otoliths is high. Comparison between whole and sectioned otoliths showed that the former significantly under-estimated the age of fish older than 10 years (p<0.01). A large proportion (68%) of the individual growth rates derived from mark-recapture data were below those predicted by the otolith based von Bertalanffy growth model (p<0.01). This was attributed to the negative influence of external tags, as hydroids, frequently occurring on the tags of recaptured fish, were observed to cause severe lesions and in some cases, extensive fin damage. This brings into question the use of mark-recapture studies to calculate growth of some species. The effects of sampling design and sample size on age and growth estimation were assessed. The minimum sample size required to accurately estimate growth and mortality, and the effects of using either random or stratified sampling procedures were tested. Decimal and integer ageing both produced similar estimates of von Bertalanffy growth parameters, growth curves, spawner biomass-per-recruit (SB/R) and fishing mortality (F) estimates. Sampling monthly throughout the year and collecting data in a single large sample provided similar growth curves, von Bertalanffy, F and SB/R estimates. The data showed that estimates based on less than 300 random samples were unreliable. However, accurate growth parameter estimates were achievable with less than 200 samples if the sample was stratified with 10 or more samples per 2 cm size class. An investigation into the reproductive biology of A. argyrozona within the Tsitsikamma National Park revealed that they were serial spawning late gonochorists. The size at 50% maturity (L₅₀) was estimated at 292 and 297 mm FL for females and males, respectively. Both monthly gonadosomatic indices and macroscopically determined ovarian stages strongly suggest that A. argyrozona within the Tsitsikamma National Park spawn in the austral summer between November and April. The presence of post-ovulatory follicles (POF's) confirmed the six month spawning season, while monthly proportions of early (0-6 hour old) POF's showed that spawning frequency was highest (once every 1-2 days) from December to March. Although spawning season was more highly correlated to photoperiod (r = 0.859) than temperature (r = -0.161), the daily proportion of spawning fish was strongly correlated (r = 0.93) to ambient temperature over the range 9-22⁰C. Both spawning frequency and season increased with fish length. As a result of the allometric relationship between annual fecundity and fish mass a 3 kg fish was calculated to produce 5 fold more eggs per kilogram of body weight than a fish of 1 kg. In addition to producing more eggs per unit weight each year, larger fish also produce significantly larger eggs. Adult emigration and larval dispersal of A. argyrozona from the Tsitsikamma National Park (TNP), South Africa, were investigated using mark-recapture data and Acoustic Doppler Current Profiler measurements of currents. Tagging data showed that adult carpenter were mainly resident, with a small proportion (7%) leaving the TNP in both easterly and westerly directions. No relationship was found between fish movement patterns and fish size or time-at-liberty. Current patterns suggest that eggs and larvae spawned within the TNP are mainly transported eastwards towards established nursery grounds; the median estimated distance moved was 299 km (range 42-561 km) in 30 days (time to flexion). Given this pattern of ichthyoplankton dispersal together with the fact that adult carpenter within the TNP display a high degree of residency and that they are much more abundant than in adjacent fishing grounds (cpue = 23 times greater), it appears that the TNP protects a viable carpenter spawner population capable of seeding adjacent fishing grounds. Fishery independent biomass surveys and commercial linefish catch returns were used to elucidate the spatial patterns of A. argyrozona distributed along the South African continental shelf. Two distinct areas of abundance were determined, one on the central and the other on the eastern Agulhas Bank. Tagging studies revealed little exchange between them. Two distinct nursery areas were identified. These data suggest that in each area juvenile A. argyrozona settle and move inshore, and then move offshore as they grow. Otolith readability and growth rates varied between regions, with fish from the Eastern Cape having the lowest average percentage error and the slowest growth rates, readability decreased westward. L₅₀ varied between the central and eastern Agulhas Bank as did mass at length. Based on the distribution of carpenter, variability in otolith readability, mass at length, variation in growth and size at maturity, it is concluded that carpenter exist as two separate stocks, one on the central Agulhas Bank and the other on the eastern Agulhas Bank. SB/R, fecundity-per-recruit (Egg/R) and yield-per-recruit (Y/R) models were used to model both South African carpenter stocks. Owing to the allometric relationship between annual fecundity and individual size, Egg/R ratios were between 40 and 74% of SB/R at equivalent F. Egg/R ratios account for allometric increases in fecundity with size/age, and are therefore regarded as more accurate estimates of reproductive potential, and biological reference points for per-recruit analysis should wherever possible be based on this quantum. It is shown that the current length at first capture (lc) (250 mm TL) and F (at M = 0.1) will reduce Egg/R to 6.41% of the pristine value in the Eastern Cape and between 6.06 and 14.15% on the central Agulhas Bank, indicating that both stocks are heavily over exploited. An increase in lc from 250 to 350 mm TL and a 70% reduction in commercial fishing effort is recommended to attain a target reference point of 40% Egg/RF=0. Bag frequency analysis indicates that a reduction in daily bag limit from 10 to 4 fish.person¹.day⁻¹ would effect an equivalent reduction in recreational F. The trawl bycatch of carpenter is only 3% of the reported line catch, consequently restrictions to this fishery are not recommended.
- Full Text:
- Date Issued: 2005
- Authors: Brouwer, Stephen Leonard
- Date: 2005
- Subjects: Reef fishes -- South Africa Sparidae -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5241 , http://hdl.handle.net/10962/d1005084
- Description: Carpenter, Argyrozona argyrozona (Valenciennes, 1830), is an endemic South African sparid fish. They form an important component of the commercial linefishery on the South African east coast, where they are the third most important species landed. Recent investigations revealed that the catch per unit effort (cpue) of this species has declined markedly since the early 1900’s. Despite these declines and the importance of this resource, remarkably little biological information on this species exists for providing management advice. This thesis investigates the life history of carpenter, particularly those aspects that are used for management. This includes an investigation into the stock distribution and identification of nursery areas, and an assessment of age, growth, reproduction and movement patterns. Age and growth was assessed using methods based on both otoliths and mark-recapture. Transverse sagittal sections from the Tsitsikamma National Park showed clear opaque and translucent growth increments. Marginal growth zone analysis and mark-recapture of chemically tagged fish (Oxytetracycline) revealed that these were deposited on an annual basis: opaque in summer and translucent in winter. A. argyrozona were found to be long lived (up to 27 years) and slow growing. Within reader (between counts) and between readers average percent error (APE) was 5.3 and 1.8, respectively, showing that readability of carpenter otoliths is high. Comparison between whole and sectioned otoliths showed that the former significantly under-estimated the age of fish older than 10 years (p<0.01). A large proportion (68%) of the individual growth rates derived from mark-recapture data were below those predicted by the otolith based von Bertalanffy growth model (p<0.01). This was attributed to the negative influence of external tags, as hydroids, frequently occurring on the tags of recaptured fish, were observed to cause severe lesions and in some cases, extensive fin damage. This brings into question the use of mark-recapture studies to calculate growth of some species. The effects of sampling design and sample size on age and growth estimation were assessed. The minimum sample size required to accurately estimate growth and mortality, and the effects of using either random or stratified sampling procedures were tested. Decimal and integer ageing both produced similar estimates of von Bertalanffy growth parameters, growth curves, spawner biomass-per-recruit (SB/R) and fishing mortality (F) estimates. Sampling monthly throughout the year and collecting data in a single large sample provided similar growth curves, von Bertalanffy, F and SB/R estimates. The data showed that estimates based on less than 300 random samples were unreliable. However, accurate growth parameter estimates were achievable with less than 200 samples if the sample was stratified with 10 or more samples per 2 cm size class. An investigation into the reproductive biology of A. argyrozona within the Tsitsikamma National Park revealed that they were serial spawning late gonochorists. The size at 50% maturity (L₅₀) was estimated at 292 and 297 mm FL for females and males, respectively. Both monthly gonadosomatic indices and macroscopically determined ovarian stages strongly suggest that A. argyrozona within the Tsitsikamma National Park spawn in the austral summer between November and April. The presence of post-ovulatory follicles (POF's) confirmed the six month spawning season, while monthly proportions of early (0-6 hour old) POF's showed that spawning frequency was highest (once every 1-2 days) from December to March. Although spawning season was more highly correlated to photoperiod (r = 0.859) than temperature (r = -0.161), the daily proportion of spawning fish was strongly correlated (r = 0.93) to ambient temperature over the range 9-22⁰C. Both spawning frequency and season increased with fish length. As a result of the allometric relationship between annual fecundity and fish mass a 3 kg fish was calculated to produce 5 fold more eggs per kilogram of body weight than a fish of 1 kg. In addition to producing more eggs per unit weight each year, larger fish also produce significantly larger eggs. Adult emigration and larval dispersal of A. argyrozona from the Tsitsikamma National Park (TNP), South Africa, were investigated using mark-recapture data and Acoustic Doppler Current Profiler measurements of currents. Tagging data showed that adult carpenter were mainly resident, with a small proportion (7%) leaving the TNP in both easterly and westerly directions. No relationship was found between fish movement patterns and fish size or time-at-liberty. Current patterns suggest that eggs and larvae spawned within the TNP are mainly transported eastwards towards established nursery grounds; the median estimated distance moved was 299 km (range 42-561 km) in 30 days (time to flexion). Given this pattern of ichthyoplankton dispersal together with the fact that adult carpenter within the TNP display a high degree of residency and that they are much more abundant than in adjacent fishing grounds (cpue = 23 times greater), it appears that the TNP protects a viable carpenter spawner population capable of seeding adjacent fishing grounds. Fishery independent biomass surveys and commercial linefish catch returns were used to elucidate the spatial patterns of A. argyrozona distributed along the South African continental shelf. Two distinct areas of abundance were determined, one on the central and the other on the eastern Agulhas Bank. Tagging studies revealed little exchange between them. Two distinct nursery areas were identified. These data suggest that in each area juvenile A. argyrozona settle and move inshore, and then move offshore as they grow. Otolith readability and growth rates varied between regions, with fish from the Eastern Cape having the lowest average percentage error and the slowest growth rates, readability decreased westward. L₅₀ varied between the central and eastern Agulhas Bank as did mass at length. Based on the distribution of carpenter, variability in otolith readability, mass at length, variation in growth and size at maturity, it is concluded that carpenter exist as two separate stocks, one on the central Agulhas Bank and the other on the eastern Agulhas Bank. SB/R, fecundity-per-recruit (Egg/R) and yield-per-recruit (Y/R) models were used to model both South African carpenter stocks. Owing to the allometric relationship between annual fecundity and individual size, Egg/R ratios were between 40 and 74% of SB/R at equivalent F. Egg/R ratios account for allometric increases in fecundity with size/age, and are therefore regarded as more accurate estimates of reproductive potential, and biological reference points for per-recruit analysis should wherever possible be based on this quantum. It is shown that the current length at first capture (lc) (250 mm TL) and F (at M = 0.1) will reduce Egg/R to 6.41% of the pristine value in the Eastern Cape and between 6.06 and 14.15% on the central Agulhas Bank, indicating that both stocks are heavily over exploited. An increase in lc from 250 to 350 mm TL and a 70% reduction in commercial fishing effort is recommended to attain a target reference point of 40% Egg/RF=0. Bag frequency analysis indicates that a reduction in daily bag limit from 10 to 4 fish.person¹.day⁻¹ would effect an equivalent reduction in recreational F. The trawl bycatch of carpenter is only 3% of the reported line catch, consequently restrictions to this fishery are not recommended.
- Full Text:
- Date Issued: 2005
Puerulus and early juvenile recruitment of the rock lobster jasus lalandii in relation to the environment at Lüderitz Bay, Namibia
- Authors: Keulder, Felicia Juanita
- Date: 2005
- Subjects: Jasus lalandii , Lobster fisheries -- Namibia , Lobster culture -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5315 , http://hdl.handle.net/10962/d1005160 , Jasus lalandii , Lobster fisheries -- Namibia , Lobster culture -- Namibia
- Description: A global decline in the lobster fishery has necessitated the growout of wild-caught postlarvae (pueruli) on farms to meet the worlds lobster demand. A limited knowledge on puerulus settlement in the West Coast rock lobster (Jasus lalandii) constitutes a major barrier for J. lalandii culture development in Southern Africa. As an extension of an existing long-term puerulus monitoring program of the Ministry of Fisheries and Marine Resources of Namibia, the present study monitored puerulus recruitment (supply), puerulus condition and juvenile growth of J. lalandii and their relationship with environmental variables on an oyster farm at Lüderitz Bay, Namibia. Implications for lobster aquaculture and fisheries management are discussed. Oyster bags, crates and collectors were sampled daily, weekly and bimonthly, for pueruli and juveniles, respectively, between August 2001 and July 2003 to establish spatialtemporal patterns in their distribution. Animals were transported to the laboratory for morphometric analyses where they were staged as puerulus (Pt = transparent; Pp = pigmented) and juvenile lobsters. The carapace lengths (0.1mm CL) and wet weights (0.01gram) of animals were recorded. Carapace length frequencies were subjected to Modal Progression analysis to identify early juvenile cohorts and calculate their growths. The weight-length ratios calculated and percentage fat content were used as indices of nutritional condition. Seasonal peaks in puerulus and juvenile abundance were estimated using Periodic Regression analysis. The relationships of puerulus and juvenile abundance with respect to sea surface temperature (SST), wind speed-direction, moon phase, swell and tidal range were established using time lag analysis (ADL). Transparent pueruli were randomly distributed on oyster bags and crates, and also between collector sites, suggesting that they have no particular settlement preference for certain areas on these structures (p>0.05; n=150). Pigmented puerulus (p<0.05; n=566) and juveniles (p<0.05; n=3528) preferred structurally complex structures that provided better shelter such as crates, which were more sheltered from sea swells, compared to oyster bags. Among oyster rafts, pigmented puerulus and juveniles preferred occupying the sheltered and centred raft areas, which provided better protection from wave action, compared to exposed raft areas, which were exposed to the incoming swell. Puerulus and juvenile lobster appeared to recolonise adjacent bags and crates, and possibly migrate to the substrate and off the farm due to the disturbance of the habitat during harvesting. The booth crevice collector was more efficient in collecting puerulus possibly due to the high structurally complex habitat and the better shelter they provided compared to the hogshair collector. The occupation of structurally complex habitats by early benthic stages may be related to morphological changes associated with metamorphosis. Puerulus settlement peaked during early spring (August-September) and was related to low sea surface temperatures (12.3°C), strong south winds, and moderate swells in the week preceding settlement. These conditions are synonymous with the “spring upwelling” season of the Lüderitz upwelling cell in the central Benguela current region. Puerulus nutritional condition peaked during this period possibly due to high levels of planktonic food (due to high nutrients from upwelling) that was available to the late stage phyllosoma larvae further offshore. A “good” puerulus settlement year during 2000 was associated with lower than average SST (11.6°C) and strong south winds and was followed by “poor” puerulus settlement years during 2001 and 2002 when higher than average SST were experienced with below average wind speeds experienced during 2001 only. Puerulus of J. lalandii recruited in high numbers into Lüderitz Bay during the new moon, full moon and last quarter moon phases by making use of the increased tides during these phases of the lunar cycle. Peak juvenile abundance during early summer (November-December) lagged by 8 weeks was significantly correlated with peak puerulus abundance. Puerulus size was similar (8.5–9.7mm CL) over the study period. Juvenile cohorts, 9.9-20.6mm CL in size recruited in 2 distinct waves in August 2001-June 2002 and July 2002-February 2003. The 2001/2002 recruits had higher monthly growth increments and better nutritional condition compared to 2002/2003 recruits. Peak frequencies of 2nd moult juveniles (9.9- 10.8mm CL) occurred in September of both recruitment events with nutritional condition being poorest during the 2002/2003 event. The nutritional condition of the settling puerulus did not appear to be related to the subsequent growth of juvenile lobster. These preliminary results suggest that pueruli recruit once a year mainly during late winter/ early spring under conditions typical of coastal upwelling in the Benguela current near Lüderitz. It appears that puerulus settlement is driven by favourable shoreward currents, which help in transporting puerulus to their settlement grounds. Puerulus supply is highly variable between years, which appears to be consistent with a highly variable Benguela environment. The oyster farm supported a substantial standing stock averaging 123 800 lobster per day (range: 22 600-325 300 lobster per day) of which 26 600 were puerulus and 97 200 were juveniles, that may have been harvested once off on any given day during the sample period. Monthly harvesting of the total lobster standing stock during the one and a half year sampling period was just over 2 million lobsters (505 700 pueruli and 1.85 million juveniles) and would potentially have been sufficient seed for a 200 ton lobster production in puerulus lobster growout facilities. In the light of high inter-annual variation in puerulus settlement observed at Lüderitz, the seed supply at the Lüderitz oyster farm is clearly limited and therefore it is prudent that other sites of high puerulus settlement is established before large commercial scale lobster growout can commence. The migration of lobster off the farm suggested that these lobsters potentially recruit to the fishery and therefore harvesting the entire standing stock on the farm may have adverse negative effects on the wild fishery. A policy decision will be required as to whether more efficient harvesting of lobster from the farm should be allowed. If puerulus removal in J. lalandii for aquaculture is allowed in the near future, it should be conducted on an experimental scale or small commercial scale until the potential effects on recruitment into the fishery are clearer.
- Full Text:
- Date Issued: 2005
- Authors: Keulder, Felicia Juanita
- Date: 2005
- Subjects: Jasus lalandii , Lobster fisheries -- Namibia , Lobster culture -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5315 , http://hdl.handle.net/10962/d1005160 , Jasus lalandii , Lobster fisheries -- Namibia , Lobster culture -- Namibia
- Description: A global decline in the lobster fishery has necessitated the growout of wild-caught postlarvae (pueruli) on farms to meet the worlds lobster demand. A limited knowledge on puerulus settlement in the West Coast rock lobster (Jasus lalandii) constitutes a major barrier for J. lalandii culture development in Southern Africa. As an extension of an existing long-term puerulus monitoring program of the Ministry of Fisheries and Marine Resources of Namibia, the present study monitored puerulus recruitment (supply), puerulus condition and juvenile growth of J. lalandii and their relationship with environmental variables on an oyster farm at Lüderitz Bay, Namibia. Implications for lobster aquaculture and fisheries management are discussed. Oyster bags, crates and collectors were sampled daily, weekly and bimonthly, for pueruli and juveniles, respectively, between August 2001 and July 2003 to establish spatialtemporal patterns in their distribution. Animals were transported to the laboratory for morphometric analyses where they were staged as puerulus (Pt = transparent; Pp = pigmented) and juvenile lobsters. The carapace lengths (0.1mm CL) and wet weights (0.01gram) of animals were recorded. Carapace length frequencies were subjected to Modal Progression analysis to identify early juvenile cohorts and calculate their growths. The weight-length ratios calculated and percentage fat content were used as indices of nutritional condition. Seasonal peaks in puerulus and juvenile abundance were estimated using Periodic Regression analysis. The relationships of puerulus and juvenile abundance with respect to sea surface temperature (SST), wind speed-direction, moon phase, swell and tidal range were established using time lag analysis (ADL). Transparent pueruli were randomly distributed on oyster bags and crates, and also between collector sites, suggesting that they have no particular settlement preference for certain areas on these structures (p>0.05; n=150). Pigmented puerulus (p<0.05; n=566) and juveniles (p<0.05; n=3528) preferred structurally complex structures that provided better shelter such as crates, which were more sheltered from sea swells, compared to oyster bags. Among oyster rafts, pigmented puerulus and juveniles preferred occupying the sheltered and centred raft areas, which provided better protection from wave action, compared to exposed raft areas, which were exposed to the incoming swell. Puerulus and juvenile lobster appeared to recolonise adjacent bags and crates, and possibly migrate to the substrate and off the farm due to the disturbance of the habitat during harvesting. The booth crevice collector was more efficient in collecting puerulus possibly due to the high structurally complex habitat and the better shelter they provided compared to the hogshair collector. The occupation of structurally complex habitats by early benthic stages may be related to morphological changes associated with metamorphosis. Puerulus settlement peaked during early spring (August-September) and was related to low sea surface temperatures (12.3°C), strong south winds, and moderate swells in the week preceding settlement. These conditions are synonymous with the “spring upwelling” season of the Lüderitz upwelling cell in the central Benguela current region. Puerulus nutritional condition peaked during this period possibly due to high levels of planktonic food (due to high nutrients from upwelling) that was available to the late stage phyllosoma larvae further offshore. A “good” puerulus settlement year during 2000 was associated with lower than average SST (11.6°C) and strong south winds and was followed by “poor” puerulus settlement years during 2001 and 2002 when higher than average SST were experienced with below average wind speeds experienced during 2001 only. Puerulus of J. lalandii recruited in high numbers into Lüderitz Bay during the new moon, full moon and last quarter moon phases by making use of the increased tides during these phases of the lunar cycle. Peak juvenile abundance during early summer (November-December) lagged by 8 weeks was significantly correlated with peak puerulus abundance. Puerulus size was similar (8.5–9.7mm CL) over the study period. Juvenile cohorts, 9.9-20.6mm CL in size recruited in 2 distinct waves in August 2001-June 2002 and July 2002-February 2003. The 2001/2002 recruits had higher monthly growth increments and better nutritional condition compared to 2002/2003 recruits. Peak frequencies of 2nd moult juveniles (9.9- 10.8mm CL) occurred in September of both recruitment events with nutritional condition being poorest during the 2002/2003 event. The nutritional condition of the settling puerulus did not appear to be related to the subsequent growth of juvenile lobster. These preliminary results suggest that pueruli recruit once a year mainly during late winter/ early spring under conditions typical of coastal upwelling in the Benguela current near Lüderitz. It appears that puerulus settlement is driven by favourable shoreward currents, which help in transporting puerulus to their settlement grounds. Puerulus supply is highly variable between years, which appears to be consistent with a highly variable Benguela environment. The oyster farm supported a substantial standing stock averaging 123 800 lobster per day (range: 22 600-325 300 lobster per day) of which 26 600 were puerulus and 97 200 were juveniles, that may have been harvested once off on any given day during the sample period. Monthly harvesting of the total lobster standing stock during the one and a half year sampling period was just over 2 million lobsters (505 700 pueruli and 1.85 million juveniles) and would potentially have been sufficient seed for a 200 ton lobster production in puerulus lobster growout facilities. In the light of high inter-annual variation in puerulus settlement observed at Lüderitz, the seed supply at the Lüderitz oyster farm is clearly limited and therefore it is prudent that other sites of high puerulus settlement is established before large commercial scale lobster growout can commence. The migration of lobster off the farm suggested that these lobsters potentially recruit to the fishery and therefore harvesting the entire standing stock on the farm may have adverse negative effects on the wild fishery. A policy decision will be required as to whether more efficient harvesting of lobster from the farm should be allowed. If puerulus removal in J. lalandii for aquaculture is allowed in the near future, it should be conducted on an experimental scale or small commercial scale until the potential effects on recruitment into the fishery are clearer.
- Full Text:
- Date Issued: 2005
The assessment and management of bycatch and discards in the South African demersal trawl fishery
- Authors: Walmsley, Sarah Ann
- Date: 2005
- Subjects: Bycatches (Fisheries) Fishery management -- South Africa Fisheries -- South Africa Trawls and trawling -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5228 , http://hdl.handle.net/10962/d1005071
- Description: Over the past few decades it has become recognised that an ecosystem approach is required to manage world fisheries. Management strategies must ensure that non-target (bycatch) as well as target catches are sustainable. To achieve this, detailed commercial catch and biological information is required. The composition of catches made by trawlers operating off the south and west coasts of South Africa was investigated. Distinct fishing areas were identified on each coast, based on target species and fishing depth. Catch composition differed markedly among the areas defined. Although hake Merluccius sp. dominated South Coast catches, a large proportion of the catch was composed of bycatch. On the West Coast, hake dominated catches and this domination increased with increasing depth. On both coasts approximately 90% of the observed nominal catch was processed and landed. Estimates of annual discards suggested that the fishery discarded 38 thousand tons of fish per annum (16% of the nominal trawl catch). The data also indicated that hake discarding, the capture of linefish and the increased targeting of high value species might be cause for concern. Spatial analysis indicated that a variety of factors such as trawling position, catch size and catch composition affects bycatch dynamics. The monkfish Lophius vomerinus is a common bycatch species that has been increasingly targeted by demersal trawlers. This study showed that L. vomerinus is a slow-growing, long-lived species (West Coast males L∞ = 68.50cm TL, t₀ = -1.69yr, K = 0.10yr⁻¹; West Coast females L∞ = 110.23cm TL, t₀ = -1.54yr, K = 0.05yr⁻¹; South Coast sexes combined L∞ = 70.12cm TL, t₀ = - 0.80yr, K = 0.11yr⁻¹), that matures at approximately 6 years of age. These traits could have serious management implications for the species. Per-recruit analysis suggested that the stock might be overexploited, although further investigation is required to confirm this. Solutions were suggested for each of the concerns raised, taking cognisance of the differences observed between the South and West Coasts and the economic dependence of South Coast companies on bycatch. The needs of future research were considered.
- Full Text:
- Date Issued: 2005
- Authors: Walmsley, Sarah Ann
- Date: 2005
- Subjects: Bycatches (Fisheries) Fishery management -- South Africa Fisheries -- South Africa Trawls and trawling -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5228 , http://hdl.handle.net/10962/d1005071
- Description: Over the past few decades it has become recognised that an ecosystem approach is required to manage world fisheries. Management strategies must ensure that non-target (bycatch) as well as target catches are sustainable. To achieve this, detailed commercial catch and biological information is required. The composition of catches made by trawlers operating off the south and west coasts of South Africa was investigated. Distinct fishing areas were identified on each coast, based on target species and fishing depth. Catch composition differed markedly among the areas defined. Although hake Merluccius sp. dominated South Coast catches, a large proportion of the catch was composed of bycatch. On the West Coast, hake dominated catches and this domination increased with increasing depth. On both coasts approximately 90% of the observed nominal catch was processed and landed. Estimates of annual discards suggested that the fishery discarded 38 thousand tons of fish per annum (16% of the nominal trawl catch). The data also indicated that hake discarding, the capture of linefish and the increased targeting of high value species might be cause for concern. Spatial analysis indicated that a variety of factors such as trawling position, catch size and catch composition affects bycatch dynamics. The monkfish Lophius vomerinus is a common bycatch species that has been increasingly targeted by demersal trawlers. This study showed that L. vomerinus is a slow-growing, long-lived species (West Coast males L∞ = 68.50cm TL, t₀ = -1.69yr, K = 0.10yr⁻¹; West Coast females L∞ = 110.23cm TL, t₀ = -1.54yr, K = 0.05yr⁻¹; South Coast sexes combined L∞ = 70.12cm TL, t₀ = - 0.80yr, K = 0.11yr⁻¹), that matures at approximately 6 years of age. These traits could have serious management implications for the species. Per-recruit analysis suggested that the stock might be overexploited, although further investigation is required to confirm this. Solutions were suggested for each of the concerns raised, taking cognisance of the differences observed between the South and West Coasts and the economic dependence of South Coast companies on bycatch. The needs of future research were considered.
- Full Text:
- Date Issued: 2005
The biophysical dynamics of the Lower Shire River Floodplain fisheries in Malawi
- Authors: Chimatiro, Sloans Kalumba
- Date: 2005
- Subjects: Shire River Valley (Malawi and Mozambique) Fisheries -- Malawi
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5243 , http://hdl.handle.net/10962/d1005086
- Description: Fishes of African floodplains typically comprise populations having short life cycles, relatively few age groups, more generalised feeding behaviour, and which experience spawning success that is strongly influenced by abiotic factors such as hydrological regime of the river, climatic seasonality and habitat characteristics. In addition, African river-floodplain ecosystems do not have appropriate predictive models for estimating yield in these ecosystems. While most predictive models developed to date for floodplain fisheries have taken into account morpho-edaphic factors, they have generally excluded climatic factors as a mega-determinant of the variability of floodplain fisheries. The principle aim of this thesis has been to develop a predictive management model that incorporates data on essential biological aspects of the target species, characteristics of the habitat as well as overall climatic factors, and thus allow for adaptive management of the fisheries in a continuously fluctuating floodplain environment. Lower Shire Floodplain (34 ⁰ 45’ – 35 ⁰ E and 16 ⁰ 00’-17 ⁰ 15’ S) in Malawi, one of the major rivers-floodplains in the Zambezi Basin, was used to test this type of model. The major hypothesis tested in this study was that “the dynamics of the fishery of Lower Shire Floodplain are driven by and adapted to the seasonal, but predictable, hydro-climatic regime of the floodplain”. The specific objectives were: to describe the floodplain’s climate and hydrological pattern; to develop a quantitative characterisation of the major habitats of the Lower Shire Floodplain; to assess the fishery in terms of size, gear utilisation, gear selectivity and yield; to assess the biological parameters of the target species, necessary for the management of the fishery; to analyse how water fluctuation in the floodplain affects the recruitment and life history of the two target species; and to develop of a predictive hydro-climatic model to benefit the management of the fisheries. The climate of the floodplain was characterised by low (765 ± 198 mm) and fairly variable (Cv = 27%) rainfall, which largely occurred between December and January. The area was generally humid (mean RH 68%), with mild to hot (25- 33ºC) and variable monthly mean diurnal (12ºC) temperature. Four quarterly hydro-climatic seasons were identified and comprised: Quarter 1 (Jul-Sep) characterised by hot, dry weather with a low flood regime; Quarter 2 (Oct-Dec) hot, windy, wet weather with low-but-rising flood regime; Quarter 3 (Jan-Mar) hot humid, wet weather with the flood regime at peak; and Quarter 4 (Apr-Jun) humid and cool weather with receding flood regime. The annual hydrograph of the floodplain was represented by four categories of flood regime as: low (Jul-Sept), low-but-rising (Oct-Dec), peak (Jan- Mar), and falling (Apr-Jun). The floodplain experienced a water deficit of 95.1 mm.year⁻¹, and it was hypothesised that ground water recharge maintained water in the floodplain the rest of the year. Three major habitats were identified in the floodplain. The river-floodplain, characterised by deep fast-flowing water, sandy substrate and little emergent vegetation; the permanently connected lagoons, were shallow (≤ 2 m) with sandymud bottom and slow flowing water; and the seasonally connected lagoons had slowflowing stagnant water, with comparatively more emergent and floating vegetation. Physicochemical characteristics of the habitats varied significantly with hydroclimatic seasons (one-way ANOVA, p ≤ 0.05), indicating the influence of flood regime, which joined the habitats in a non-equilibrial spatial distribution. Consequently, during receding and low flood regimes river-floodplain and permanently connected lagoons exhibited similar characteristics while all three habitats had similar characteristics during the rising and peak flood regimes. It was, therefore, concluded that in floodplains, habitats shift horizontally and vertically according to the water level. Gill nets, cast nets, long line, and fish traps accounted for 99% of the total count of gears, and hence considered the major fishing sectors. Two principal species in the floodplain were the catfish Clarias gariepinus and the cichlid Oreochromis mossambicus. Length-at-maximum-selectivity (ø) and length-at-50%-sexual-maturity (Lm₅₀) for each of the two species showed that although they were selected into the four fishing sectors at lengths above maturity, maximum selectivity into the long line occurred at a length before maturity for O. mossambicus. In addition, the width of the gamma selectivity function (σ) indicated that a considerable proportion of juveniles of the two species were also selected. Therefore, it was decided that management for the floodplain be centred on controlling over-fishing and preserving the spawner stock, by banning seine and mosquito nets, and closing river-floodplain and permanently connected lagoons to fishing during the low flood regime. There were significant seasonal variations in CPUE, lowest in the low flood, and highest during the peak flood regime. Sectioned otoliths were used to determine the age and growth of the two principal species in the floodplain. Marginal zone analysis revealed that annulus formation in all the species occurred during the period of low air and water temperatures, high evaporation and receding water levels, hence a high rate of desiccation and negative water budget. For O. mossambicus, maximum age reached was 6 years while in C. gariepinus it was 9 years. The 3-parameter von Bertalanffy growth model adequately described growth as lt = 177.6(1-e⁻·⁴⁴⁽t ⁺ ¹·⁴³⁾) mm TL for O. mossambicus and lt = 502.9(1-e⁻°·³¹⁽t ⁺ ¹·⁹²⁾) mm TL for C. gariepinus. Female O. mossambicus reached 50%-sexual-maturity at 109 mm SL, while males matured at 105 mm, and both male and female C. gariepinus reached Lm₅₀ at 249 mm SL. The breeding seasons of both O. mossambicus and Clarias gariepinus were between September and March, with modal peaks in January and November, respectively. The annual total mortality rates (Z) were 0.62 ± 0.18 yr⁻¹ for O. mossambicus and 0.93 ± 0.47 yr⁻¹ for C. gariepinus. The mean empirical estimates of natural mortality (M) were 0.46 yr⁻¹ for O. mossambicus and 0.50 year⁻¹ for C. gariepinus, and fishing mortality (F) was calculated as 0.16 yr⁻¹ for O. mossambicus and 0.43 yr⁻¹ for C. gariepinus. The overall exploitation level (Z/K) was 1.41 for O. mossambicus and 3.01 for C. gariepinus. Given that the Z/K ratio was >1, it was asserted that both O. mossambicus and C. gariepinus were mortality-dominated and fairly heavily exploited. However, potential for sustainable exploitation existed since both species showed signs of resilience due short longevity and high rate of natural mortality. Given the limitation of simple exponential models of fish mortality and growth under the situation of seasonal fluctuation of water levels, a simple predictive hydroclimatic- fisheries model was developed. The model predicted the life-history and production parameters fairly accurately (0.53 ≤ r² ≥ 0.98, p ≤ 0.05), and showed that environmental and biological events in the floodplain significantly (0.43 ≤ r² ≥ 0.91, p ≤ 0.05) followed the periodic function of time (day-of-the-year), hence, strongly seasonal. In addition, the flood-pulse preceded all the major biological events, with predicted phase lags established at 55.6º for peak flood, 157.2º, 260.1º, 334.6º and 341.4º for condition factor for O. mossambicus, recruitment, spawning period for O. mossambicus and C. gariepinus, respectively. Therefore, it was recommended that water obstruction on the Shire River must ensure sufficient water flow during the peak flood and spawning period to allow flooding and inundation of the floodplain in order to create habitat favourable for spawning and feeding as well as improve recruitment.
- Full Text:
- Date Issued: 2005
- Authors: Chimatiro, Sloans Kalumba
- Date: 2005
- Subjects: Shire River Valley (Malawi and Mozambique) Fisheries -- Malawi
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5243 , http://hdl.handle.net/10962/d1005086
- Description: Fishes of African floodplains typically comprise populations having short life cycles, relatively few age groups, more generalised feeding behaviour, and which experience spawning success that is strongly influenced by abiotic factors such as hydrological regime of the river, climatic seasonality and habitat characteristics. In addition, African river-floodplain ecosystems do not have appropriate predictive models for estimating yield in these ecosystems. While most predictive models developed to date for floodplain fisheries have taken into account morpho-edaphic factors, they have generally excluded climatic factors as a mega-determinant of the variability of floodplain fisheries. The principle aim of this thesis has been to develop a predictive management model that incorporates data on essential biological aspects of the target species, characteristics of the habitat as well as overall climatic factors, and thus allow for adaptive management of the fisheries in a continuously fluctuating floodplain environment. Lower Shire Floodplain (34 ⁰ 45’ – 35 ⁰ E and 16 ⁰ 00’-17 ⁰ 15’ S) in Malawi, one of the major rivers-floodplains in the Zambezi Basin, was used to test this type of model. The major hypothesis tested in this study was that “the dynamics of the fishery of Lower Shire Floodplain are driven by and adapted to the seasonal, but predictable, hydro-climatic regime of the floodplain”. The specific objectives were: to describe the floodplain’s climate and hydrological pattern; to develop a quantitative characterisation of the major habitats of the Lower Shire Floodplain; to assess the fishery in terms of size, gear utilisation, gear selectivity and yield; to assess the biological parameters of the target species, necessary for the management of the fishery; to analyse how water fluctuation in the floodplain affects the recruitment and life history of the two target species; and to develop of a predictive hydro-climatic model to benefit the management of the fisheries. The climate of the floodplain was characterised by low (765 ± 198 mm) and fairly variable (Cv = 27%) rainfall, which largely occurred between December and January. The area was generally humid (mean RH 68%), with mild to hot (25- 33ºC) and variable monthly mean diurnal (12ºC) temperature. Four quarterly hydro-climatic seasons were identified and comprised: Quarter 1 (Jul-Sep) characterised by hot, dry weather with a low flood regime; Quarter 2 (Oct-Dec) hot, windy, wet weather with low-but-rising flood regime; Quarter 3 (Jan-Mar) hot humid, wet weather with the flood regime at peak; and Quarter 4 (Apr-Jun) humid and cool weather with receding flood regime. The annual hydrograph of the floodplain was represented by four categories of flood regime as: low (Jul-Sept), low-but-rising (Oct-Dec), peak (Jan- Mar), and falling (Apr-Jun). The floodplain experienced a water deficit of 95.1 mm.year⁻¹, and it was hypothesised that ground water recharge maintained water in the floodplain the rest of the year. Three major habitats were identified in the floodplain. The river-floodplain, characterised by deep fast-flowing water, sandy substrate and little emergent vegetation; the permanently connected lagoons, were shallow (≤ 2 m) with sandymud bottom and slow flowing water; and the seasonally connected lagoons had slowflowing stagnant water, with comparatively more emergent and floating vegetation. Physicochemical characteristics of the habitats varied significantly with hydroclimatic seasons (one-way ANOVA, p ≤ 0.05), indicating the influence of flood regime, which joined the habitats in a non-equilibrial spatial distribution. Consequently, during receding and low flood regimes river-floodplain and permanently connected lagoons exhibited similar characteristics while all three habitats had similar characteristics during the rising and peak flood regimes. It was, therefore, concluded that in floodplains, habitats shift horizontally and vertically according to the water level. Gill nets, cast nets, long line, and fish traps accounted for 99% of the total count of gears, and hence considered the major fishing sectors. Two principal species in the floodplain were the catfish Clarias gariepinus and the cichlid Oreochromis mossambicus. Length-at-maximum-selectivity (ø) and length-at-50%-sexual-maturity (Lm₅₀) for each of the two species showed that although they were selected into the four fishing sectors at lengths above maturity, maximum selectivity into the long line occurred at a length before maturity for O. mossambicus. In addition, the width of the gamma selectivity function (σ) indicated that a considerable proportion of juveniles of the two species were also selected. Therefore, it was decided that management for the floodplain be centred on controlling over-fishing and preserving the spawner stock, by banning seine and mosquito nets, and closing river-floodplain and permanently connected lagoons to fishing during the low flood regime. There were significant seasonal variations in CPUE, lowest in the low flood, and highest during the peak flood regime. Sectioned otoliths were used to determine the age and growth of the two principal species in the floodplain. Marginal zone analysis revealed that annulus formation in all the species occurred during the period of low air and water temperatures, high evaporation and receding water levels, hence a high rate of desiccation and negative water budget. For O. mossambicus, maximum age reached was 6 years while in C. gariepinus it was 9 years. The 3-parameter von Bertalanffy growth model adequately described growth as lt = 177.6(1-e⁻·⁴⁴⁽t ⁺ ¹·⁴³⁾) mm TL for O. mossambicus and lt = 502.9(1-e⁻°·³¹⁽t ⁺ ¹·⁹²⁾) mm TL for C. gariepinus. Female O. mossambicus reached 50%-sexual-maturity at 109 mm SL, while males matured at 105 mm, and both male and female C. gariepinus reached Lm₅₀ at 249 mm SL. The breeding seasons of both O. mossambicus and Clarias gariepinus were between September and March, with modal peaks in January and November, respectively. The annual total mortality rates (Z) were 0.62 ± 0.18 yr⁻¹ for O. mossambicus and 0.93 ± 0.47 yr⁻¹ for C. gariepinus. The mean empirical estimates of natural mortality (M) were 0.46 yr⁻¹ for O. mossambicus and 0.50 year⁻¹ for C. gariepinus, and fishing mortality (F) was calculated as 0.16 yr⁻¹ for O. mossambicus and 0.43 yr⁻¹ for C. gariepinus. The overall exploitation level (Z/K) was 1.41 for O. mossambicus and 3.01 for C. gariepinus. Given that the Z/K ratio was >1, it was asserted that both O. mossambicus and C. gariepinus were mortality-dominated and fairly heavily exploited. However, potential for sustainable exploitation existed since both species showed signs of resilience due short longevity and high rate of natural mortality. Given the limitation of simple exponential models of fish mortality and growth under the situation of seasonal fluctuation of water levels, a simple predictive hydroclimatic- fisheries model was developed. The model predicted the life-history and production parameters fairly accurately (0.53 ≤ r² ≥ 0.98, p ≤ 0.05), and showed that environmental and biological events in the floodplain significantly (0.43 ≤ r² ≥ 0.91, p ≤ 0.05) followed the periodic function of time (day-of-the-year), hence, strongly seasonal. In addition, the flood-pulse preceded all the major biological events, with predicted phase lags established at 55.6º for peak flood, 157.2º, 260.1º, 334.6º and 341.4º for condition factor for O. mossambicus, recruitment, spawning period for O. mossambicus and C. gariepinus, respectively. Therefore, it was recommended that water obstruction on the Shire River must ensure sufficient water flow during the peak flood and spawning period to allow flooding and inundation of the floodplain in order to create habitat favourable for spawning and feeding as well as improve recruitment.
- Full Text:
- Date Issued: 2005
The life history patterns of the polychaete, Terebrasabella heterouncinata, a pest of cultured abalone
- Authors: Simon, Carol Anne
- Date: 2005
- Subjects: Polychaeta -- Physiology Sabellidae -- Physiology Abalones -- Diseases Polychaeta -- Reproduction Sabellidae -- Reproduction Abalone culture -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5336 , http://hdl.handle.net/10962/d1005632
- Description: Terebrasabella heterouncinata is a small K-selected sabellid polychaete. It is a simultaneous hermaphrodite with a semi-continuous mode of reproduction, producing relatively few large eggs that are brooded within the parental burrow until the larvae emerge, to settle on the growing edge of the abalone shell. Despite its low fecundity, this worm has become problematic on abalone farms in South Africa. The present study was conducted to gain an understanding of the life history patterns of T. helerouncinata to determine how they contributed to the success of these worms under altered conditions. This study demonstrated that conditions prevalent on abalone farms were conducive to enhancing the reproductive success of this worm, and suggests that larger, more fecund worms may have been selected for in the decade that these worms have been present on the farms. Increased nutrient availability, and possibly the increased stability of the farm environment relative to its natural environment, has led to a 1.5-fold increase in the average size of the worms. Body size was found to be positively correlated with brood size, and this resulted in worms on farms brooding 3 to 4.5 times more offspring at a time than worms from wild abalone. The ability to increase the number of eggs produced at a time may have been limited by the fact that these worms have only two ovaries. Thus, the increase in fecundity may have been related primarily to the increase in the rate at which the eggs were laid by the worms on the farms, and the increase in the coelomic space available for the storage of these rapidly developing eggs. The ability to increase the rate at which oocytes develop may be related to the vitellogenic mechanisms employed by these worms. Vitellogenic oocytes are able to incorporate high molecular weight yolk precursors from the surrounding coelomic fluid through endocytotic activity. This may allow the oocytes to increase the rate at which they incorporate yolk material under conditions of nutrient enrichment. The increase in fecundity did not occur at the expense of offspring size and, presumably, quality. The increased reproductive output on the farms was compounded by a proportionate increase in the number of reproducing worms within the population. In addition, these worms are long-lived (worms from farmed abalone reached a maximum age of approximately 40 months) and exhibit negligible senescence. Thus, their reproductive output did not change significantly with an increase in age. Furthermore, the proportion of the reproductive worms did not decrease with an increase in age. Thus, within the age range tested, worms of all ages have the potential to make equal contributions to population growth. While diet and abalone stocking density could not be identified as having a significant effect on reproductive output and infestation rate under intensive culture conditions, it was demonstrated that in a naïve abalone population, the total intensity of infestation increased exponentially with time. This increase may be a consequence of an increase in fertilisation success. These worms continuously produce entaquasperm that are released into the water column. The sperm are collected by other individuals that then store the sperm in a single spermatheca. The ability to store sperm relieves individuals of a dependence on the synchronisation of spawning of eggs and sperm. As the population size and density increases, there could be more individuals releasing sperm into the water column, resulting in a continuous supply of sperm. The increased production of eggs would therefore not be constrained by a lack of sperm. The stored sperm are released into the brood chamber to fertilise eggs as they are laid, and this would probably increase the fertilisation success in the species. This study also provides evidence to suggest that reproduction in this worm has a seasonal component. Future studies should concentrate on measuring fertilisation success in greater detail, measuring the effect of season on reproduction, determining whether there are genetic differences between worms on farmed and wild abalone and determining whether wild worms have similar life-spans and age-related fecundity as worms on farms.
- Full Text:
- Date Issued: 2005
- Authors: Simon, Carol Anne
- Date: 2005
- Subjects: Polychaeta -- Physiology Sabellidae -- Physiology Abalones -- Diseases Polychaeta -- Reproduction Sabellidae -- Reproduction Abalone culture -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5336 , http://hdl.handle.net/10962/d1005632
- Description: Terebrasabella heterouncinata is a small K-selected sabellid polychaete. It is a simultaneous hermaphrodite with a semi-continuous mode of reproduction, producing relatively few large eggs that are brooded within the parental burrow until the larvae emerge, to settle on the growing edge of the abalone shell. Despite its low fecundity, this worm has become problematic on abalone farms in South Africa. The present study was conducted to gain an understanding of the life history patterns of T. helerouncinata to determine how they contributed to the success of these worms under altered conditions. This study demonstrated that conditions prevalent on abalone farms were conducive to enhancing the reproductive success of this worm, and suggests that larger, more fecund worms may have been selected for in the decade that these worms have been present on the farms. Increased nutrient availability, and possibly the increased stability of the farm environment relative to its natural environment, has led to a 1.5-fold increase in the average size of the worms. Body size was found to be positively correlated with brood size, and this resulted in worms on farms brooding 3 to 4.5 times more offspring at a time than worms from wild abalone. The ability to increase the number of eggs produced at a time may have been limited by the fact that these worms have only two ovaries. Thus, the increase in fecundity may have been related primarily to the increase in the rate at which the eggs were laid by the worms on the farms, and the increase in the coelomic space available for the storage of these rapidly developing eggs. The ability to increase the rate at which oocytes develop may be related to the vitellogenic mechanisms employed by these worms. Vitellogenic oocytes are able to incorporate high molecular weight yolk precursors from the surrounding coelomic fluid through endocytotic activity. This may allow the oocytes to increase the rate at which they incorporate yolk material under conditions of nutrient enrichment. The increase in fecundity did not occur at the expense of offspring size and, presumably, quality. The increased reproductive output on the farms was compounded by a proportionate increase in the number of reproducing worms within the population. In addition, these worms are long-lived (worms from farmed abalone reached a maximum age of approximately 40 months) and exhibit negligible senescence. Thus, their reproductive output did not change significantly with an increase in age. Furthermore, the proportion of the reproductive worms did not decrease with an increase in age. Thus, within the age range tested, worms of all ages have the potential to make equal contributions to population growth. While diet and abalone stocking density could not be identified as having a significant effect on reproductive output and infestation rate under intensive culture conditions, it was demonstrated that in a naïve abalone population, the total intensity of infestation increased exponentially with time. This increase may be a consequence of an increase in fertilisation success. These worms continuously produce entaquasperm that are released into the water column. The sperm are collected by other individuals that then store the sperm in a single spermatheca. The ability to store sperm relieves individuals of a dependence on the synchronisation of spawning of eggs and sperm. As the population size and density increases, there could be more individuals releasing sperm into the water column, resulting in a continuous supply of sperm. The increased production of eggs would therefore not be constrained by a lack of sperm. The stored sperm are released into the brood chamber to fertilise eggs as they are laid, and this would probably increase the fertilisation success in the species. This study also provides evidence to suggest that reproduction in this worm has a seasonal component. Future studies should concentrate on measuring fertilisation success in greater detail, measuring the effect of season on reproduction, determining whether there are genetic differences between worms on farmed and wild abalone and determining whether wild worms have similar life-spans and age-related fecundity as worms on farms.
- Full Text:
- Date Issued: 2005
Towards the development of a protocol for rearing juvenile rock lobster, Jasus lalandii
- Authors: Esterhuizen, J. A
- Date: 2005
- Subjects: Lobsters -- Growth , Lobster fisheries -- South Africa , Crustacea -- Growth , Crustacea -- South Africa , Jasus lalandii , Lobster culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5328 , http://hdl.handle.net/10962/d1005174 , Lobsters -- Growth , Lobster fisheries -- South Africa , Crustacea -- Growth , Crustacea -- South Africa , Jasus lalandii , Lobster culture
- Description: The diversification of current aquaculture practise in South Africa is crucial for the future development of the industry. The rock lobster, Jasus lalandii has been identified as a possible candidate species for shore based culture in systems similar to those used for abalone farming. Reduced Total Allowable Catch (TAC's) and an increased minimum legal size were implemented as management strategies to relieve fishing pressure on natural stocks of J. lalandii, and in turn led to increased market demand and a possible niche for farmed lobsters. High puerulus settlement along the Namibian coast, together with other favourable aquaculture attributes, indicate that the commercial grow out of wild harvested juveniles could be feasible. The aim of study was to investigate the feasibility of growing out rock lobsters in shore based systems in Namibia and South Africa. The experimental objectives of the project were to investigate the nutritional requirements, as well as the effect of stocking density and tank design on growth and survival of J. lalandii. The economic viability of shore based rock lobster farming was then evaluated based on the experimental results and typical capital requirements of an abalone farm in South Africa. Puerulus and early juvenile rock lobsters were collected in Luderitz, Namibia and transported to HIK Abalone Farm in Hermanus, South Africa where they were acclimated in black fibre glass tanks in a flow through system. The pueruli were stocked at 50, 75, 100 and 125/m² and early juveniles at 20, 30, 40 and 50/m² to test the effect of density on growth and survival. A comparative dietary study with both size classes was conducted using a mussel diet (Choromytilus meridionalis and Mytilus galloprovincialis), a commercial shrimp feed diet and a rotational diet comprising both mussels and shrimp feed. Tanks provided with "v-shaped" asbestos hides, PVC hides and no hides were compared to test the effect on growth rate and survival of pueruli. All treatments were conducted in triplicate. Temperatures were recorded twice daily while water quality parameters were tested every second week. The results indicate that density had a significant effect on growth and survival on post-pueruli. An initial stocking density of 75 post-pueruli/m² is regarded as optimal both in terms of the growth rate and biomass production per tank. No differences in growth and survival rates were attained in the early juvenile size class. This indicates that higher densities can be used to rear juvenile J. lalandii. No significant differences were obtained in growth rate when reared under different hide conditions although asbestos hides yielded significantly higher survival rates (93.3 %) compared to the tanks provided with PVC hides (74.04 %) and no hides (77.8 %, p≤0.05). As a result of the high survival rate observed in tanks provided with "V-shaped" asbestos hides, these tanks also yielded higher biomass production per tank (297.8 grams) compared to the tanks provided with PVC hides and no hides (261.09 and 260.5 grams respectively). In the diet trials, growth rates of post pueruli and juvenile lobsters fed the mussel and rotational (mussel and shrimp feed) diets did not differ significantly, however, growth rates of lobsters fed the shrimp feed only diet was significantly lower than both the mussel and rotational diets (p≤0.05). Lobsters fed the mussel diet yielded significantly higher survival rates compared to lobsters fed either the rotational diet or shrimp feed diet only. An imbalance in the fatty acid profile of the shrimp feed could have been a major contributing factor to the poor growth and survival in lobsters fed the shrimp feed only diet as the level of linoleic acid (LOA) was exceptionally high resulting in a high (n -6):(n-3) ratio (1.01) compared to the mussel and rotational diets (0.17 and 0.56 respectively). The low level of arachidonic acid (ARA) in the shrimp feed diet could be a further contributing factor explaning for the poor growth and survival of juvenile rock lobsters. An economic feasibility study was conducted at the end of the experimental phase by modelling a hypothetical shore based rock lobster farm. A projection of production costs and revenues was based on the typical costs of a shore based abalone farm and the current market prices for wild harvested J. lalandii. The economic viability was evaluated using benefit-cost ratios, payback period, internal rate of return and breakeven analysis. Sensitivity analyses revealed that the projected lobster growth and survival rates were the main biological factors influencing the economic feasibility of the hypothetical rock lobster farm. An assumed four year grow out period at a low stocking density yielded more lucrative internal rate of return (IRR), benefit-cost ratio, payback period and net present values (NPV) than a five year grow out period at a high density. The four year grow out scenario proved to be more robust to the fluctuating Rand/US$ exchange rate and could accommodate a lower lobster survival rate. Results presented in this study indicate that rock lobster farming is a marginal commercial prospect based on current production performance and costs. Further research to develop effective puerulus collection techniques as well as to make lobster grow out technology more cost effective is required.
- Full Text:
- Date Issued: 2005
- Authors: Esterhuizen, J. A
- Date: 2005
- Subjects: Lobsters -- Growth , Lobster fisheries -- South Africa , Crustacea -- Growth , Crustacea -- South Africa , Jasus lalandii , Lobster culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5328 , http://hdl.handle.net/10962/d1005174 , Lobsters -- Growth , Lobster fisheries -- South Africa , Crustacea -- Growth , Crustacea -- South Africa , Jasus lalandii , Lobster culture
- Description: The diversification of current aquaculture practise in South Africa is crucial for the future development of the industry. The rock lobster, Jasus lalandii has been identified as a possible candidate species for shore based culture in systems similar to those used for abalone farming. Reduced Total Allowable Catch (TAC's) and an increased minimum legal size were implemented as management strategies to relieve fishing pressure on natural stocks of J. lalandii, and in turn led to increased market demand and a possible niche for farmed lobsters. High puerulus settlement along the Namibian coast, together with other favourable aquaculture attributes, indicate that the commercial grow out of wild harvested juveniles could be feasible. The aim of study was to investigate the feasibility of growing out rock lobsters in shore based systems in Namibia and South Africa. The experimental objectives of the project were to investigate the nutritional requirements, as well as the effect of stocking density and tank design on growth and survival of J. lalandii. The economic viability of shore based rock lobster farming was then evaluated based on the experimental results and typical capital requirements of an abalone farm in South Africa. Puerulus and early juvenile rock lobsters were collected in Luderitz, Namibia and transported to HIK Abalone Farm in Hermanus, South Africa where they were acclimated in black fibre glass tanks in a flow through system. The pueruli were stocked at 50, 75, 100 and 125/m² and early juveniles at 20, 30, 40 and 50/m² to test the effect of density on growth and survival. A comparative dietary study with both size classes was conducted using a mussel diet (Choromytilus meridionalis and Mytilus galloprovincialis), a commercial shrimp feed diet and a rotational diet comprising both mussels and shrimp feed. Tanks provided with "v-shaped" asbestos hides, PVC hides and no hides were compared to test the effect on growth rate and survival of pueruli. All treatments were conducted in triplicate. Temperatures were recorded twice daily while water quality parameters were tested every second week. The results indicate that density had a significant effect on growth and survival on post-pueruli. An initial stocking density of 75 post-pueruli/m² is regarded as optimal both in terms of the growth rate and biomass production per tank. No differences in growth and survival rates were attained in the early juvenile size class. This indicates that higher densities can be used to rear juvenile J. lalandii. No significant differences were obtained in growth rate when reared under different hide conditions although asbestos hides yielded significantly higher survival rates (93.3 %) compared to the tanks provided with PVC hides (74.04 %) and no hides (77.8 %, p≤0.05). As a result of the high survival rate observed in tanks provided with "V-shaped" asbestos hides, these tanks also yielded higher biomass production per tank (297.8 grams) compared to the tanks provided with PVC hides and no hides (261.09 and 260.5 grams respectively). In the diet trials, growth rates of post pueruli and juvenile lobsters fed the mussel and rotational (mussel and shrimp feed) diets did not differ significantly, however, growth rates of lobsters fed the shrimp feed only diet was significantly lower than both the mussel and rotational diets (p≤0.05). Lobsters fed the mussel diet yielded significantly higher survival rates compared to lobsters fed either the rotational diet or shrimp feed diet only. An imbalance in the fatty acid profile of the shrimp feed could have been a major contributing factor to the poor growth and survival in lobsters fed the shrimp feed only diet as the level of linoleic acid (LOA) was exceptionally high resulting in a high (n -6):(n-3) ratio (1.01) compared to the mussel and rotational diets (0.17 and 0.56 respectively). The low level of arachidonic acid (ARA) in the shrimp feed diet could be a further contributing factor explaning for the poor growth and survival of juvenile rock lobsters. An economic feasibility study was conducted at the end of the experimental phase by modelling a hypothetical shore based rock lobster farm. A projection of production costs and revenues was based on the typical costs of a shore based abalone farm and the current market prices for wild harvested J. lalandii. The economic viability was evaluated using benefit-cost ratios, payback period, internal rate of return and breakeven analysis. Sensitivity analyses revealed that the projected lobster growth and survival rates were the main biological factors influencing the economic feasibility of the hypothetical rock lobster farm. An assumed four year grow out period at a low stocking density yielded more lucrative internal rate of return (IRR), benefit-cost ratio, payback period and net present values (NPV) than a five year grow out period at a high density. The four year grow out scenario proved to be more robust to the fluctuating Rand/US$ exchange rate and could accommodate a lower lobster survival rate. Results presented in this study indicate that rock lobster farming is a marginal commercial prospect based on current production performance and costs. Further research to develop effective puerulus collection techniques as well as to make lobster grow out technology more cost effective is required.
- Full Text:
- Date Issued: 2005
Towards the development of a protocol for the selection of probiotics in marine fish larviculture
- Authors: Vine, Niall Gordon
- Date: 2005
- Subjects: Marine fishes -- Larvae Bacteria Fishes -- Microbiology Fish culture
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5329 , http://hdl.handle.net/10962/d1005175
- Description: Manipulation or control of the microbiological aquaculture environment has been identified as an important focus area for future hatchery development. Subsequently, alternatives to obtain control of the microbiological environment are being sought of which the field of probiotics appears highly promising. Probiotics are usually selected based on various in vitro characteristics, however, the methods used differ and are sometimes unsuccessful due to poor experimentation. The aim of this work is to contribute towards the development of a protocol for the in vitro screening of bacterial candidate probiotics for marine fish larviculture. To reduce the number of candidate probiotics to be tested in vivo, various in vitro experiments need to be conducted, each screening for a particular mode of action – antagonism towards pathogen through production of antimicrobial compounds, growth and attachment to fish intestinal mucus, and the production of other beneficial compounds such as vitamins, fatty-acids and digestive enzymes. A total of 108 bacteria species were isolated from the digestive tract of the adult common clownfish, Amphiprion percula to screen for potential probiotics to be used in clownfish larval rearing. The antagonistic compounds assay identified twelve isolates which showed antagonism towards two or more aquatic pathogens. This was followed by an in vitro test that involved growing the organisms in fish intestinal mucus and modeling their growth parameters. A ranking index (RI) was developed using the lag period (λ) and doubling time (td) of the organism, where (1over λ x td) x 100. Five candidate probionts (AP1-AP5) with varied growth parameters were used for further in vitro experiments. The attachment to mucus assay introduced a novel tool for quantifying competition for attachment sites between candidate probionts and pathogens on mucus. Candidate probiont Pseudoalteromonas AP5 reduced the attachment ability of Vibrio alginolyticus when added before the pathogen and partially out-competed the pathogen for attachment sites when added second. In vitro screening for the production of beneficial compounds tested the candidate probiotics’ ability to produce digestive enzymes - trypsin, lipase and alkaline phosphatase as well as carotenoids and vitamin C. Candidate probiont Pseudoalteromonas AP5 produced high levels of the enzymes (98.2, 34.1 and 91.3 mU product liberated.ml⁻¹, respectively) and contained carotenoids while Kocuria AP4 contained carotenoids but produced low quantities of enzymes (7.8, 0 and 59 mU product liberated.ml⁻¹, respectively). None of the candidate probiotics produced vitamin C. To eliminate potential pathogenic or toxic candidate probionts, Artemia nauplii were exposed to each candidate probiont and the percentage Artemia mortality after 24-hours was determined. Candidate probiont AP2 caused high mortality of Artemia nauplii (98.4%) and was excluded from further studies. Identification of candidate probionts AP3-AP5 was performed using 16S-rDNA molecular techniques and the bacteria were assigned the names Bacillus AP3, Kocuria AP4 and Pseudoalteromonas AP5, respectively. Two methods of larval probiont delivery were tested – attachment to Artemia, and in-water delivery. Attachment to Artemia was high for both Kocuria AP4 and Pseudoalteromonas AP5 (7.2 x10³ and 2.7x10⁴ bacteria.nauplius⁻¹, respectively) while the in-water viability experiment showed that Kocuria AP4 comprised 23.9% of the total culturable water microflora after 24 hours while Pseudoalteromonas AP5 contributed 100%. To validate the findings from the in vitro experiments, in vivo trials using clownfish larvae were performed. Of the four candidate probiotics tested, only Kocuria AP4 showed potential to increase larval survival. In vitro tests produced a better understanding of the possible mode of action and strategies of competition between bacteria, however, the number of criteria in which a candidate probiont is successful in vitro may not be the best predictor for its effectiveness in vivo. Commercial studies that reduce between-treatment variation are required to test predictions about the most suitable probiont or combinations thereof.
- Full Text:
- Date Issued: 2005
- Authors: Vine, Niall Gordon
- Date: 2005
- Subjects: Marine fishes -- Larvae Bacteria Fishes -- Microbiology Fish culture
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5329 , http://hdl.handle.net/10962/d1005175
- Description: Manipulation or control of the microbiological aquaculture environment has been identified as an important focus area for future hatchery development. Subsequently, alternatives to obtain control of the microbiological environment are being sought of which the field of probiotics appears highly promising. Probiotics are usually selected based on various in vitro characteristics, however, the methods used differ and are sometimes unsuccessful due to poor experimentation. The aim of this work is to contribute towards the development of a protocol for the in vitro screening of bacterial candidate probiotics for marine fish larviculture. To reduce the number of candidate probiotics to be tested in vivo, various in vitro experiments need to be conducted, each screening for a particular mode of action – antagonism towards pathogen through production of antimicrobial compounds, growth and attachment to fish intestinal mucus, and the production of other beneficial compounds such as vitamins, fatty-acids and digestive enzymes. A total of 108 bacteria species were isolated from the digestive tract of the adult common clownfish, Amphiprion percula to screen for potential probiotics to be used in clownfish larval rearing. The antagonistic compounds assay identified twelve isolates which showed antagonism towards two or more aquatic pathogens. This was followed by an in vitro test that involved growing the organisms in fish intestinal mucus and modeling their growth parameters. A ranking index (RI) was developed using the lag period (λ) and doubling time (td) of the organism, where (1over λ x td) x 100. Five candidate probionts (AP1-AP5) with varied growth parameters were used for further in vitro experiments. The attachment to mucus assay introduced a novel tool for quantifying competition for attachment sites between candidate probionts and pathogens on mucus. Candidate probiont Pseudoalteromonas AP5 reduced the attachment ability of Vibrio alginolyticus when added before the pathogen and partially out-competed the pathogen for attachment sites when added second. In vitro screening for the production of beneficial compounds tested the candidate probiotics’ ability to produce digestive enzymes - trypsin, lipase and alkaline phosphatase as well as carotenoids and vitamin C. Candidate probiont Pseudoalteromonas AP5 produced high levels of the enzymes (98.2, 34.1 and 91.3 mU product liberated.ml⁻¹, respectively) and contained carotenoids while Kocuria AP4 contained carotenoids but produced low quantities of enzymes (7.8, 0 and 59 mU product liberated.ml⁻¹, respectively). None of the candidate probiotics produced vitamin C. To eliminate potential pathogenic or toxic candidate probionts, Artemia nauplii were exposed to each candidate probiont and the percentage Artemia mortality after 24-hours was determined. Candidate probiont AP2 caused high mortality of Artemia nauplii (98.4%) and was excluded from further studies. Identification of candidate probionts AP3-AP5 was performed using 16S-rDNA molecular techniques and the bacteria were assigned the names Bacillus AP3, Kocuria AP4 and Pseudoalteromonas AP5, respectively. Two methods of larval probiont delivery were tested – attachment to Artemia, and in-water delivery. Attachment to Artemia was high for both Kocuria AP4 and Pseudoalteromonas AP5 (7.2 x10³ and 2.7x10⁴ bacteria.nauplius⁻¹, respectively) while the in-water viability experiment showed that Kocuria AP4 comprised 23.9% of the total culturable water microflora after 24 hours while Pseudoalteromonas AP5 contributed 100%. To validate the findings from the in vitro experiments, in vivo trials using clownfish larvae were performed. Of the four candidate probiotics tested, only Kocuria AP4 showed potential to increase larval survival. In vitro tests produced a better understanding of the possible mode of action and strategies of competition between bacteria, however, the number of criteria in which a candidate probiont is successful in vitro may not be the best predictor for its effectiveness in vivo. Commercial studies that reduce between-treatment variation are required to test predictions about the most suitable probiont or combinations thereof.
- Full Text:
- Date Issued: 2005
A development and management framework for a new Octopus vulgaris fishery in South Africa
- Authors: Oosthuizen, Ané
- Date: 2004
- Subjects: Common octopus -- South Africa Octopus fisheries -- South Africa Octopus fisheries -- South Africa -- Economic aspects Fishery management -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5255 , http://hdl.handle.net/10962/d1005098
- Description: A new policy incorporating an operational protocol was developed for the establishment of new fisheries in South Africa. The common octopus, Octopus vulgaris was used as a candidate species for the project. The operational protocol consisted of a three-phased development framework, namely information gathering (Phase 0), an experimental fishery (Phase 1) and the final implementation of a commercial fishery (Phase 2). The present study focussed on phase 0 of this theoretical framework and protocol and was implemented by using a proposed octopus pot fishery in South Africa as a case study. Phase 0 included a desktop study, information gathering in the field, an economic feasibility study and the formulation of a Fishery Management Plan and experimental design for the fishery. Information gaps identified during the desktop study were addressed during field investigations into the population structure and biology of O. vulgaris along the southeast coast. Immature females were found to use the intertidal area to feed and grow before migrating to the subtidal area to mature and spawn. Mean size differed substantially between intertidal and subtidal areas, with larger octopus found subtidally. Age and growth trials using tetracycline as a marker showed that O. vulgaris deposit daily growth lines in their beaks. A genetic study showed that there is most likely only one panmitic population along the coast. The economic feasibility study indicated that a longline pot fishery could be feasible provided a 30% catch in 6600 pots/month is attained. Only existing, debt-free vessels should be used in this fishery. The Fishery Management Plan proposed in this study includes management measures such as effort limitation of licences and gear, size restrictions, vessel monitoring systems, and observer programmes. Based on the population dynamics and biology of O. vulgaris it is suggested that a precautionary approach to developing fisheries for this species in both the inter- and subtidal areas along the South African coast.
- Full Text:
- Date Issued: 2004
- Authors: Oosthuizen, Ané
- Date: 2004
- Subjects: Common octopus -- South Africa Octopus fisheries -- South Africa Octopus fisheries -- South Africa -- Economic aspects Fishery management -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5255 , http://hdl.handle.net/10962/d1005098
- Description: A new policy incorporating an operational protocol was developed for the establishment of new fisheries in South Africa. The common octopus, Octopus vulgaris was used as a candidate species for the project. The operational protocol consisted of a three-phased development framework, namely information gathering (Phase 0), an experimental fishery (Phase 1) and the final implementation of a commercial fishery (Phase 2). The present study focussed on phase 0 of this theoretical framework and protocol and was implemented by using a proposed octopus pot fishery in South Africa as a case study. Phase 0 included a desktop study, information gathering in the field, an economic feasibility study and the formulation of a Fishery Management Plan and experimental design for the fishery. Information gaps identified during the desktop study were addressed during field investigations into the population structure and biology of O. vulgaris along the southeast coast. Immature females were found to use the intertidal area to feed and grow before migrating to the subtidal area to mature and spawn. Mean size differed substantially between intertidal and subtidal areas, with larger octopus found subtidally. Age and growth trials using tetracycline as a marker showed that O. vulgaris deposit daily growth lines in their beaks. A genetic study showed that there is most likely only one panmitic population along the coast. The economic feasibility study indicated that a longline pot fishery could be feasible provided a 30% catch in 6600 pots/month is attained. Only existing, debt-free vessels should be used in this fishery. The Fishery Management Plan proposed in this study includes management measures such as effort limitation of licences and gear, size restrictions, vessel monitoring systems, and observer programmes. Based on the population dynamics and biology of O. vulgaris it is suggested that a precautionary approach to developing fisheries for this species in both the inter- and subtidal areas along the South African coast.
- Full Text:
- Date Issued: 2004
Age, growth and yield-per-recruit analysis of ndunduma Diplotaxodon limnothrissa (Teleostei: Cichlidae), in the southeastern arm of Lake Malawi
- Authors: Kanyerere, Geoffrey Zantute
- Date: 2004
- Subjects: Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5214 , http://hdl.handle.net/10962/d1005057 , Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Description: Diplotaxodon limnothrissa Turner (1995) is a widely distributed species occurring throughout Lake Malawi, extending from the surface to a depth of at least 220m. It is probably the most abundant cichlid in the lake with biomass estimates of around 87 000 tonnes in the pelagic zone alone. The species is exploited commercially in the southern part of the lake but since its inception the fishery has never been assessed. As such this study investigates some aspects of age and growth of the species besides applying a yield-per-recruit analysis to assess the status of the fishery. Analysis of sectioned sagittal otoliths revealed that D. limnothrissa is fast growing and relatively long-lived species, attaining ages in excess of 10 years. Growth in length was rapid in immature fish, with fish attaining almost half of their maximum size within their first year. Le ngth-at-age was described by the von Bertalanffy growth model with combined-sex growth described as Lt = 211.21(1-exp(- 0.24(t+1.36))) mm TL. Total, natural and fishing mortalities were estimated at 0.76 yr⁻¹, 0.31 yr⁻¹ and 0.45 yr⁻¹ respectively. Per-recruit analysis indicated that the D. limnothrissa stock in the southeast arm of the lake is fully exploited as indicated by the current spawner biomass-per-recruit ratios of 31-55% (SB/R)F=0. Modelling indicated that the current age-at-capture (2.67 years) is lower than the age at which yield is optimised (> 5 years) based on the F₀·₁ harvesting strategy. It is, therefore, recommended that the age-at-capture should be increased from 2.67 to 5 years to optimise yield.
- Full Text:
- Date Issued: 2004
- Authors: Kanyerere, Geoffrey Zantute
- Date: 2004
- Subjects: Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5214 , http://hdl.handle.net/10962/d1005057 , Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Description: Diplotaxodon limnothrissa Turner (1995) is a widely distributed species occurring throughout Lake Malawi, extending from the surface to a depth of at least 220m. It is probably the most abundant cichlid in the lake with biomass estimates of around 87 000 tonnes in the pelagic zone alone. The species is exploited commercially in the southern part of the lake but since its inception the fishery has never been assessed. As such this study investigates some aspects of age and growth of the species besides applying a yield-per-recruit analysis to assess the status of the fishery. Analysis of sectioned sagittal otoliths revealed that D. limnothrissa is fast growing and relatively long-lived species, attaining ages in excess of 10 years. Growth in length was rapid in immature fish, with fish attaining almost half of their maximum size within their first year. Le ngth-at-age was described by the von Bertalanffy growth model with combined-sex growth described as Lt = 211.21(1-exp(- 0.24(t+1.36))) mm TL. Total, natural and fishing mortalities were estimated at 0.76 yr⁻¹, 0.31 yr⁻¹ and 0.45 yr⁻¹ respectively. Per-recruit analysis indicated that the D. limnothrissa stock in the southeast arm of the lake is fully exploited as indicated by the current spawner biomass-per-recruit ratios of 31-55% (SB/R)F=0. Modelling indicated that the current age-at-capture (2.67 years) is lower than the age at which yield is optimised (> 5 years) based on the F₀·₁ harvesting strategy. It is, therefore, recommended that the age-at-capture should be increased from 2.67 to 5 years to optimise yield.
- Full Text:
- Date Issued: 2004
An investigation into the captive spawning, egg characteristics and egg quality of the mud crab (Scylla serrata) in South Africa
- Authors: Churchill, Giles John
- Date: 2004
- Subjects: Scylla serrata , Crabs -- South Africa , Scylla serrata -- South Africa , Crabs -- Eggs -- Incubation , Crabs -- Spawning
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5376 , http://hdl.handle.net/10962/d1015963
- Description: The source of a reliable supply of seed is one of the most important factors determining the success of aquaculture. At present mud crab culture is reliant on wild caught juveniles, which limits the expansion of mud crab farming globally. This, coupled with the paucity of knowledge of the spawning and egg characteristics of mud crabs, prompted the investigation into the captive spawning, incubation and egg quality of Scylla serrata in South Africa. A total of 112 mature females were caught from three estuaries in northern KwaZulu Natal and acclimated to captive conditions. Mature females were present in the estuaries throughout the year and ranged from 90 to 200 mm carapace width. Except for 40 crabs all the females spawned in captivity. On average spawning took place 38 ± 23 days after capture but was not dependent on crab size. Fecundity was significantly correlated to crab size (p = 0.026), with larger females producing more eggs. The average fecundity per batch was 5.79 ± 2.07 million eggs. Hatch success rate for all egg batches was high averaging 84 ± 6 %. Egg dropping occurred in all egg batches during incubation. On average 6.5 % of the egg mass was dropped during incubation. At the average temperature of 27⁰C eggs in the incubation system hatched within 292 ± 12 hours after extrusion. In-vitro incubation of eggs proved to be an ineffective means of incubating Scylla serrata eggs with a hatch success rate of only 25 ± 5 %. Egg quality was assessed both directly, using variables such as hatch success rate and hatch synchronicity and retrospectively by using stress tests and comparing survival of larvae from different coloured egg batches. Lipid class composition and fatty acid methyl ester content for 28 batches of eggs and 16 batches of larvae were analyzed. The biochemical composition of the egg was correlated to survival of larvae in the stress tests to ascertain if the lipid content of the eggs determines their quality. Stress tests were used to retrospectively assess egg quality. Four stressors were administered to newly hatched larvae and the LD50 values recorded. An average LD50 of 64 hours was recorded for the starvation tests, 40% for the salinity tests, 37 ppm for the formalin tests and 39.7 mg/l NH3 for the ammonia stress tests was recorded. Egg colour ranged from pale yellow to orange-red. Egg colour was not influenced by female size or the time the females spent in captivity prior to spawning. Egg colour can therefore not be used as an indicator of quality. The lipid profiles of newly extruded eggs had no effect on hatch synchronicity or hatch success rate. However, the stress tests identified female size (p ≤ 0.02), DHA content of the egg (p ≤ 0.02), Σ omega-3 fatty acids of eggs (p ≤ 0.02) and EPA content of eggs (p ≤ 0.007) as possible determinants of egg quality. Larger crabs tended to produce poorer quality eggs. Egg quality also decreased as the amount of DHA, EPA and the Σ omega-3 fatty acids decreased in the eggs. To summarize, the results of this study indicated that the following parameters affect egg quality - crab size, DHA, EPA and Σ omega-3 fatty acid content of eggs.
- Full Text:
- Date Issued: 2004
- Authors: Churchill, Giles John
- Date: 2004
- Subjects: Scylla serrata , Crabs -- South Africa , Scylla serrata -- South Africa , Crabs -- Eggs -- Incubation , Crabs -- Spawning
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5376 , http://hdl.handle.net/10962/d1015963
- Description: The source of a reliable supply of seed is one of the most important factors determining the success of aquaculture. At present mud crab culture is reliant on wild caught juveniles, which limits the expansion of mud crab farming globally. This, coupled with the paucity of knowledge of the spawning and egg characteristics of mud crabs, prompted the investigation into the captive spawning, incubation and egg quality of Scylla serrata in South Africa. A total of 112 mature females were caught from three estuaries in northern KwaZulu Natal and acclimated to captive conditions. Mature females were present in the estuaries throughout the year and ranged from 90 to 200 mm carapace width. Except for 40 crabs all the females spawned in captivity. On average spawning took place 38 ± 23 days after capture but was not dependent on crab size. Fecundity was significantly correlated to crab size (p = 0.026), with larger females producing more eggs. The average fecundity per batch was 5.79 ± 2.07 million eggs. Hatch success rate for all egg batches was high averaging 84 ± 6 %. Egg dropping occurred in all egg batches during incubation. On average 6.5 % of the egg mass was dropped during incubation. At the average temperature of 27⁰C eggs in the incubation system hatched within 292 ± 12 hours after extrusion. In-vitro incubation of eggs proved to be an ineffective means of incubating Scylla serrata eggs with a hatch success rate of only 25 ± 5 %. Egg quality was assessed both directly, using variables such as hatch success rate and hatch synchronicity and retrospectively by using stress tests and comparing survival of larvae from different coloured egg batches. Lipid class composition and fatty acid methyl ester content for 28 batches of eggs and 16 batches of larvae were analyzed. The biochemical composition of the egg was correlated to survival of larvae in the stress tests to ascertain if the lipid content of the eggs determines their quality. Stress tests were used to retrospectively assess egg quality. Four stressors were administered to newly hatched larvae and the LD50 values recorded. An average LD50 of 64 hours was recorded for the starvation tests, 40% for the salinity tests, 37 ppm for the formalin tests and 39.7 mg/l NH3 for the ammonia stress tests was recorded. Egg colour ranged from pale yellow to orange-red. Egg colour was not influenced by female size or the time the females spent in captivity prior to spawning. Egg colour can therefore not be used as an indicator of quality. The lipid profiles of newly extruded eggs had no effect on hatch synchronicity or hatch success rate. However, the stress tests identified female size (p ≤ 0.02), DHA content of the egg (p ≤ 0.02), Σ omega-3 fatty acids of eggs (p ≤ 0.02) and EPA content of eggs (p ≤ 0.007) as possible determinants of egg quality. Larger crabs tended to produce poorer quality eggs. Egg quality also decreased as the amount of DHA, EPA and the Σ omega-3 fatty acids decreased in the eggs. To summarize, the results of this study indicated that the following parameters affect egg quality - crab size, DHA, EPA and Σ omega-3 fatty acid content of eggs.
- Full Text:
- Date Issued: 2004