Towards an alternative spatial-based management approach for estuarine fisheries in South Africa, with a case study from the Sundays Estuary
- Authors: Kramer, Rachel
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/1007 , vital:20012
- Description: Estuaries are productive habitats and biologically important ecosystems which serve as juvenile nursery areas and feeding grounds for adults from a host of fish species. They are, however, threatened habitats, increasingly exposed to human disturbance and exploitation. The stocks of several South African estuary-dependent linefish species are now considered as either overexploited or collapsed. It is clear that their dependence on estuaries would warrant the inclusion of these ecosystems into marine reserve planning exercises. Since traditional management strategies (e.g. bag and size limit restrictions) have proven ineffective for estuarine fisheries, there is a need for alternative management measures, such as spatial and temporal restrictions, to ensure increased survival of juveniles and recovery of adult breeding populations. This thesis explored the potential for an ecosystem-based approach through the application of a rapid sustainability assessment technique, and a spatial-based management approach for an important fishery species, using conservation planning software. The Sundays Estuary, Eastern Cape, South Africa falls within the footprint of the Addo Elephant National Park, with a proposed expansion to include a marine protected area (MPA). However the estuaries resources were not considered during the planning of the proposed MPA. This study conducted an indicator-based sustainability assessment based on the principles of sustainable development. The results showed that present levels of exploitation, due to non-compliance and a lack of law enforcement are unsustainable. The sustainability of the Sundays Estuary had a low overall sustainability score of only 23.8%. With limited enforcement of estuarine fisheries regulations in South Africa, alternative management measures such as spatial regulations may provide a viable option forward. The sustainability of fishery resources depends on the comprehensive understanding of the fishery resource. Acoustic telemetry is a technique that has been widely adopted to infer habitat and area use patterns of fish species. The second component of this study made use of high resolution telemetry data collected on juvenile dusky kob Argyrosomus japonicus movements within the Sundays Estuary to conduct a scenario-based approach using Marxan conservation planning software. The best solution given by Marxan, in the form of a protected area for the conservation of juvenile A. japonicus in the Sundays Estuary was identified in the middle (starting 7km from the mouth) to the upper reaches (approximately 16km from the mouth) of the estuary, ultimately providing protection to tagged individuals for 61% of their time in the estuary. Although Marxan presented a best solution, the Sundays Estuary’s small size and shape, and minimal features used, was too simplistic to be included into a Marxan analysis. However, new methods and tools to analyse and plan spatial-based management options at this scale are currently being developed. Using the Sundays Estuary as a case study, a decision tree was then developed as a protocol to assist management address the challenges of effective estuarine management depending on the unique biological and socio-economic characteristics of individual estuaries in South Africa.
- Full Text:
- Date Issued: 2016
- Authors: Kramer, Rachel
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/1007 , vital:20012
- Description: Estuaries are productive habitats and biologically important ecosystems which serve as juvenile nursery areas and feeding grounds for adults from a host of fish species. They are, however, threatened habitats, increasingly exposed to human disturbance and exploitation. The stocks of several South African estuary-dependent linefish species are now considered as either overexploited or collapsed. It is clear that their dependence on estuaries would warrant the inclusion of these ecosystems into marine reserve planning exercises. Since traditional management strategies (e.g. bag and size limit restrictions) have proven ineffective for estuarine fisheries, there is a need for alternative management measures, such as spatial and temporal restrictions, to ensure increased survival of juveniles and recovery of adult breeding populations. This thesis explored the potential for an ecosystem-based approach through the application of a rapid sustainability assessment technique, and a spatial-based management approach for an important fishery species, using conservation planning software. The Sundays Estuary, Eastern Cape, South Africa falls within the footprint of the Addo Elephant National Park, with a proposed expansion to include a marine protected area (MPA). However the estuaries resources were not considered during the planning of the proposed MPA. This study conducted an indicator-based sustainability assessment based on the principles of sustainable development. The results showed that present levels of exploitation, due to non-compliance and a lack of law enforcement are unsustainable. The sustainability of the Sundays Estuary had a low overall sustainability score of only 23.8%. With limited enforcement of estuarine fisheries regulations in South Africa, alternative management measures such as spatial regulations may provide a viable option forward. The sustainability of fishery resources depends on the comprehensive understanding of the fishery resource. Acoustic telemetry is a technique that has been widely adopted to infer habitat and area use patterns of fish species. The second component of this study made use of high resolution telemetry data collected on juvenile dusky kob Argyrosomus japonicus movements within the Sundays Estuary to conduct a scenario-based approach using Marxan conservation planning software. The best solution given by Marxan, in the form of a protected area for the conservation of juvenile A. japonicus in the Sundays Estuary was identified in the middle (starting 7km from the mouth) to the upper reaches (approximately 16km from the mouth) of the estuary, ultimately providing protection to tagged individuals for 61% of their time in the estuary. Although Marxan presented a best solution, the Sundays Estuary’s small size and shape, and minimal features used, was too simplistic to be included into a Marxan analysis. However, new methods and tools to analyse and plan spatial-based management options at this scale are currently being developed. Using the Sundays Estuary as a case study, a decision tree was then developed as a protocol to assist management address the challenges of effective estuarine management depending on the unique biological and socio-economic characteristics of individual estuaries in South Africa.
- Full Text:
- Date Issued: 2016
Trends in fish community structure and recruitment in a temporarily open/closed South African estuary
- Authors: James, Nicola Caroline
- Date: 2007
- Subjects: Fish communities -- South Africa -- Eastern Cape Marine fishes -- South Africa -- Eastern Cape Estuarine fishes -- South Africa -- Eastern Cape Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5332 , http://hdl.handle.net/10962/d1005178
- Description: Long-term interannual changes in richness, abundance, diversity and structure of the fish community in the temporarily open/closed East Kleinemonde Estuary, Eastern Cape, are described and the recruitment success of two estuary-dependent marine species assessed. In addition, laboratory experiments were conducted to assess the possible role of olfaction in the recruitment process of an estuary-dependent marine fish species. Multivariate analyses of the annual marine fish communites identified two distinct groups with more species recorded during years that succeeded spring (September to November) mouth opening events than in years following no mouth opening events in spring. Interannual community stability (IMD) and seriation (IMS) also increased from the ‘other’ to the ‘spring’ years. These results highlight the importance of the timing of mouth opening to the marine fish community in a temporarily open/closed estuary. This study also made use of long-term records of daily mouth state and linked them to the recruitment of distinct year-class cohorts in two spardis with contrasting lifehistory characteristics. Lithognathus lithognathus only recruited into the estuary in years when the mouth opened between late August and January. This was linked to the limited spawning season of this species and its inability to enter closed estuaries via wave overwash events. In contrast, recruitment by Rhabdosargus holubi juveniles appeared to be uninterrupted and was not determined by the seasonality of mouth opening. This species dominates the marine-spawning component of the East Kleinemonde Estuary and its success is attributed to an extended spawning season and its ability to recruit into estuaries during both overwash and open mouth conditions. Attraction of postflexion Rhabdosargus holubi larvae to estuary, surf zone and river water was also measured using a rectangular choice chamber. In two sets of experiments, conducted during peak recruitment periods, larvae from both the surf zone and estuary mouth region selected estuary water with a significantly higher frequency than sea water. Larvae collected in the mouth region showed a stronger preference for river water than those collected in the surf zone, thus suggesting that these fish are more attracted to freshwater influenced nursery areas once they have entered the estuary than those in the surf zone. Larvae collected in the marine environment also selected surf zone water with significantly higher frequencies than estuary water or offshore sea water, thus confirming the importance of the surf zone as an interim nursery area for postflexion R. holubi.
- Full Text:
- Date Issued: 2007
- Authors: James, Nicola Caroline
- Date: 2007
- Subjects: Fish communities -- South Africa -- Eastern Cape Marine fishes -- South Africa -- Eastern Cape Estuarine fishes -- South Africa -- Eastern Cape Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5332 , http://hdl.handle.net/10962/d1005178
- Description: Long-term interannual changes in richness, abundance, diversity and structure of the fish community in the temporarily open/closed East Kleinemonde Estuary, Eastern Cape, are described and the recruitment success of two estuary-dependent marine species assessed. In addition, laboratory experiments were conducted to assess the possible role of olfaction in the recruitment process of an estuary-dependent marine fish species. Multivariate analyses of the annual marine fish communites identified two distinct groups with more species recorded during years that succeeded spring (September to November) mouth opening events than in years following no mouth opening events in spring. Interannual community stability (IMD) and seriation (IMS) also increased from the ‘other’ to the ‘spring’ years. These results highlight the importance of the timing of mouth opening to the marine fish community in a temporarily open/closed estuary. This study also made use of long-term records of daily mouth state and linked them to the recruitment of distinct year-class cohorts in two spardis with contrasting lifehistory characteristics. Lithognathus lithognathus only recruited into the estuary in years when the mouth opened between late August and January. This was linked to the limited spawning season of this species and its inability to enter closed estuaries via wave overwash events. In contrast, recruitment by Rhabdosargus holubi juveniles appeared to be uninterrupted and was not determined by the seasonality of mouth opening. This species dominates the marine-spawning component of the East Kleinemonde Estuary and its success is attributed to an extended spawning season and its ability to recruit into estuaries during both overwash and open mouth conditions. Attraction of postflexion Rhabdosargus holubi larvae to estuary, surf zone and river water was also measured using a rectangular choice chamber. In two sets of experiments, conducted during peak recruitment periods, larvae from both the surf zone and estuary mouth region selected estuary water with a significantly higher frequency than sea water. Larvae collected in the mouth region showed a stronger preference for river water than those collected in the surf zone, thus suggesting that these fish are more attracted to freshwater influenced nursery areas once they have entered the estuary than those in the surf zone. Larvae collected in the marine environment also selected surf zone water with significantly higher frequencies than estuary water or offshore sea water, thus confirming the importance of the surf zone as an interim nursery area for postflexion R. holubi.
- Full Text:
- Date Issued: 2007
Estuarine use by spotted grunter Pomadasys commersonnii in a South African estuary, as determined by acoustic telemetry
- Childs, Amber-Robyn, Cowley, Paul D, Næsje, T F, Booth, Anthony J, Potts, Warren M, Thorstad, Eva B, Økland, F
- Authors: Childs, Amber-Robyn , Cowley, Paul D , Næsje, T F , Booth, Anthony J , Potts, Warren M , Thorstad, Eva B , Økland, F
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124428 , vital:35612 , https://doi.org/10.2989/A JMS.2008.30.1.12.462
- Description: Estuaries are important in the life history and the maintenance of the diversity of coastal fish species because of their function as nursery areas for juveniles as well as feeding grounds for adults (Cyrus 1991). The dependence of many fish species on estuaries is well documented (e.g. Wallace et al. 1984, Lenanton and Potter 1987, Blaber et al. 1989, Whitfield 1990, Hoss and Thayer 1993). Spotted grunter Pomadasys commersonnii (Haemulidae) (Lacepède 1801) is an estuarine-dependent species which spawns in the KwaZulu-Natal inshore coastal waters, between August and December (Wallace 1975b, Wallace and van der Elst 1975, Harris and Cyrus 1997, 1999). The eggs and larvae are transported southwards by the Agulhas Current, and juveniles between 20 mm and 50 mm TL recruit into the KwaZulu-Natal and south-eastern Cape estuaries (Wallace and van der Elst 1975, Whitfield 1990). Juvenile spotted grunter make use of the abundant food resources in estuaries, where they grow rapidly and remain for a period of 1–3 years (Wallace and Schleyer 1979, Day et al. 1981). Upon attaining sexual maturity (at between 300 mm and 400 mm TL), they return to the marine environment (Wallace 1975b). Some adults, however, return to estuaries to feed and to regain condition after spawning (Wallace 1975b, Whitfield 1994). The return of post-spawning fish coincides with increased catches by fishers in estuaries between July and January. These events are known as ‘grunter runs’ (Wallace 1975a, Marais and Baird 1980, Marais 1988, Pradervand and Baird 2002). It is suggested that adults spend up to several months in estuaries, before moving back to sea where they undergo gonadal development and ultimately spawn (Wallace 1975b, Wallace and van der Elst 1975). It is believed that adult fish also enter estuaries in a prespawning state to gain condition en route to their spawning grounds in KwaZulu-Natal (Webb 2002).
- Full Text:
- Date Issued: 2010
- Authors: Childs, Amber-Robyn , Cowley, Paul D , Næsje, T F , Booth, Anthony J , Potts, Warren M , Thorstad, Eva B , Økland, F
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124428 , vital:35612 , https://doi.org/10.2989/A JMS.2008.30.1.12.462
- Description: Estuaries are important in the life history and the maintenance of the diversity of coastal fish species because of their function as nursery areas for juveniles as well as feeding grounds for adults (Cyrus 1991). The dependence of many fish species on estuaries is well documented (e.g. Wallace et al. 1984, Lenanton and Potter 1987, Blaber et al. 1989, Whitfield 1990, Hoss and Thayer 1993). Spotted grunter Pomadasys commersonnii (Haemulidae) (Lacepède 1801) is an estuarine-dependent species which spawns in the KwaZulu-Natal inshore coastal waters, between August and December (Wallace 1975b, Wallace and van der Elst 1975, Harris and Cyrus 1997, 1999). The eggs and larvae are transported southwards by the Agulhas Current, and juveniles between 20 mm and 50 mm TL recruit into the KwaZulu-Natal and south-eastern Cape estuaries (Wallace and van der Elst 1975, Whitfield 1990). Juvenile spotted grunter make use of the abundant food resources in estuaries, where they grow rapidly and remain for a period of 1–3 years (Wallace and Schleyer 1979, Day et al. 1981). Upon attaining sexual maturity (at between 300 mm and 400 mm TL), they return to the marine environment (Wallace 1975b). Some adults, however, return to estuaries to feed and to regain condition after spawning (Wallace 1975b, Whitfield 1994). The return of post-spawning fish coincides with increased catches by fishers in estuaries between July and January. These events are known as ‘grunter runs’ (Wallace 1975a, Marais and Baird 1980, Marais 1988, Pradervand and Baird 2002). It is suggested that adults spend up to several months in estuaries, before moving back to sea where they undergo gonadal development and ultimately spawn (Wallace 1975b, Wallace and van der Elst 1975). It is believed that adult fish also enter estuaries in a prespawning state to gain condition en route to their spawning grounds in KwaZulu-Natal (Webb 2002).
- Full Text:
- Date Issued: 2010
Thermal physiology and behavioural ecology of the white shark, carcharodon carcharias
- Authors: Gennari, Enrico
- Date: 2015
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/64002 , vital:28522
- Description: Expected release date-May 2019
- Full Text:
- Date Issued: 2015
- Authors: Gennari, Enrico
- Date: 2015
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/64002 , vital:28522
- Description: Expected release date-May 2019
- Full Text:
- Date Issued: 2015
The influence of overwash and breaching events on the spatial and temporal patterns in ichthyofauna community composition in a temporarily open/closed southern African estuary
- Authors: Tweddle, Gavin Paul
- Date: 2013
- Subjects: Estuarine fishes -- Africa, Southern Marine fishes -- Africa, Southern Fishes -- Breeding -- Africa, Southern Fishes -- Effect of habitat modification on -- Africa, Southern Fishes -- Spawning -- Africa, Southern Gobiidae -- Africa, Southern Estuaries -- Africa, Southern Estuarine ecology -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5610 , http://hdl.handle.net/10962/d1002957
- Description: This study assessed the importance of overwash and breaching events on the ichthyofaunal community structure in the medium-sized temporarily open/closed Mpekweni Estuary located on the southeast coastline of southern Africa. The fish in the littoral zone of the estuary were sampled using a 5m seine net while the channel region was sampled using two nets, a smaller meshed 30m seine net to target the estuarine spawning species and the juvenile estuarine-dependant marine spawners, and a larger meshed 50m seine net to target the larger marine and freshwater spawning species. Intensive monthly sampling over two years provided data on selected physico-chemical and biological parameters. During the two year sampling period from November 2005 to October 2007 the estuary breached in late July 2006 and remained open till the sandbar re-formed across the mouth in late December 2006. Thus, sampling encompassed three open/closed phases 1) initial closed period, 2) open period and 3) re-closed period after the berm was re-formed. The open period was divided into two phases 1) the out-flow phase and 2) the tidal phase. A total of 36 fish species representing 19 families were sampled using the various seine nets employed during the investigation. In the littoral zone, the estuarine spawners (Estuarine Utilisation Category, [EUC] I), mainly the Gobiidae, Glossogobius callidus, dominated the samples numerically and by biomass. The smaller estuarine spawning species sampled in the channel were numerically dominated by Gilchristella aestuaria in conjunction with two other EUC I species, Atherina breviceps and G. callidus. The estuarine-dependant marine spawners (EUC II), however, dominated the ichthyofaunal biomass of the channel. The abundance and biomass of the larger species targeted were dominated by estuarine-dependant marine spawning species (EUC II), principally Rhabdosargus holubi. During the closed periods of the estuary, total fish abundance and biomass displayed weak seasonal patterns. The breaching event and subsequent open period was associated with a decrease in the total abundances of fish in the littoral zone and channel of the estuary, reflecting the out-flow of estuarine biomass-rich water into the marine environment. The breaching event coincided with a shift in the community composition of the ichthyofauna, reflecting the recruitment of marine spawning species into the estuary. Numerical analysis identified two distinct spatial fish communities within the estuary, a community associated with the mouth region and one comprising the rest of the estuary. The absence of any further spatial patterns in the ichthyofaunal community structure within the Mpekweni Estuary appear to be ascribed to the virtual absence of horizontal patterns in physico-chemical and biological parameters recorded in the system. Cohort analyses were employed to determine possible recruitment events for selected estuarine and marine spawning species. The estuarine spawning species displayed continuous recruitment patterns throughout the study, which appeared to be unaffected by the breaching event. Conversely, the larger marine spawning species displayed multiple cohorts, indicating non-continuous recruitment. Subsequent retrospective analysis of cohorts for the different species identified summer recruitment peaks that coincided with the breaching event and open period. Minor recruitment of marine spawning species also occurred during overwash events. The recruitment of ichthyofauna into the estuary was quantified during three distinct hydrological events: overwash, out-flow phase immediately after breaching and tidal phase during the period when the mouth was open. Estimates of fish recruitment were highest during the outflow phase immediately after the estuary breached and declined as the estuary became tidally inundated with marine water. Although not as high as the outflow and tidal phases, recruitment was evident during overwash events. Results of the current study highlight the importance of both breaching and overwashing events in structuring the ichthyofaunal community composition in a medium-sized southern African temporarily open/closed estuary. These results are broadly in agreement with similar studies conducted both locally and in other regions of the world.
- Full Text:
- Date Issued: 2013
- Authors: Tweddle, Gavin Paul
- Date: 2013
- Subjects: Estuarine fishes -- Africa, Southern Marine fishes -- Africa, Southern Fishes -- Breeding -- Africa, Southern Fishes -- Effect of habitat modification on -- Africa, Southern Fishes -- Spawning -- Africa, Southern Gobiidae -- Africa, Southern Estuaries -- Africa, Southern Estuarine ecology -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5610 , http://hdl.handle.net/10962/d1002957
- Description: This study assessed the importance of overwash and breaching events on the ichthyofaunal community structure in the medium-sized temporarily open/closed Mpekweni Estuary located on the southeast coastline of southern Africa. The fish in the littoral zone of the estuary were sampled using a 5m seine net while the channel region was sampled using two nets, a smaller meshed 30m seine net to target the estuarine spawning species and the juvenile estuarine-dependant marine spawners, and a larger meshed 50m seine net to target the larger marine and freshwater spawning species. Intensive monthly sampling over two years provided data on selected physico-chemical and biological parameters. During the two year sampling period from November 2005 to October 2007 the estuary breached in late July 2006 and remained open till the sandbar re-formed across the mouth in late December 2006. Thus, sampling encompassed three open/closed phases 1) initial closed period, 2) open period and 3) re-closed period after the berm was re-formed. The open period was divided into two phases 1) the out-flow phase and 2) the tidal phase. A total of 36 fish species representing 19 families were sampled using the various seine nets employed during the investigation. In the littoral zone, the estuarine spawners (Estuarine Utilisation Category, [EUC] I), mainly the Gobiidae, Glossogobius callidus, dominated the samples numerically and by biomass. The smaller estuarine spawning species sampled in the channel were numerically dominated by Gilchristella aestuaria in conjunction with two other EUC I species, Atherina breviceps and G. callidus. The estuarine-dependant marine spawners (EUC II), however, dominated the ichthyofaunal biomass of the channel. The abundance and biomass of the larger species targeted were dominated by estuarine-dependant marine spawning species (EUC II), principally Rhabdosargus holubi. During the closed periods of the estuary, total fish abundance and biomass displayed weak seasonal patterns. The breaching event and subsequent open period was associated with a decrease in the total abundances of fish in the littoral zone and channel of the estuary, reflecting the out-flow of estuarine biomass-rich water into the marine environment. The breaching event coincided with a shift in the community composition of the ichthyofauna, reflecting the recruitment of marine spawning species into the estuary. Numerical analysis identified two distinct spatial fish communities within the estuary, a community associated with the mouth region and one comprising the rest of the estuary. The absence of any further spatial patterns in the ichthyofaunal community structure within the Mpekweni Estuary appear to be ascribed to the virtual absence of horizontal patterns in physico-chemical and biological parameters recorded in the system. Cohort analyses were employed to determine possible recruitment events for selected estuarine and marine spawning species. The estuarine spawning species displayed continuous recruitment patterns throughout the study, which appeared to be unaffected by the breaching event. Conversely, the larger marine spawning species displayed multiple cohorts, indicating non-continuous recruitment. Subsequent retrospective analysis of cohorts for the different species identified summer recruitment peaks that coincided with the breaching event and open period. Minor recruitment of marine spawning species also occurred during overwash events. The recruitment of ichthyofauna into the estuary was quantified during three distinct hydrological events: overwash, out-flow phase immediately after breaching and tidal phase during the period when the mouth was open. Estimates of fish recruitment were highest during the outflow phase immediately after the estuary breached and declined as the estuary became tidally inundated with marine water. Although not as high as the outflow and tidal phases, recruitment was evident during overwash events. Results of the current study highlight the importance of both breaching and overwashing events in structuring the ichthyofaunal community composition in a medium-sized southern African temporarily open/closed estuary. These results are broadly in agreement with similar studies conducted both locally and in other regions of the world.
- Full Text:
- Date Issued: 2013
Home range dynamics of spotted grunter, pomadasys commersonnii, in a South African intermittently open estuary
- Authors: O'Connell, Bronwyn Anne
- Date: 2008
- Subjects: Grunts (Fishes) -- South Africa -- Eastern Cape , Pomadasys -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fishes -- Home range , Fishes -- Home range -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5286 , http://hdl.handle.net/10962/d1005130 , Grunts (Fishes) -- South Africa -- Eastern Cape , Pomadasys -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fishes -- Home range , Fishes -- Home range -- South Africa -- Eastern Cape
- Description: The spotted grunter (Pomadasys commersonnii) is an important, estuarine-dependent, fishery species in southern Africa. Since estuaries are essential habitats in the life history of this species, the quantification of area use patterns and movements is important for fisheries management. In this study, acoustic telemetry was used to investigate movements, use of habitat and home range dynamics of spotted grunter in the small intermittently open East Kleinemonde Estuary on the Eastern Cape coast of South Africa. Nine spotted grunter (range: 326-489mm TL) were surgically equipped with uniquely coded acoustic transmitters. Positional fixes were obtained by manual tracking tagged individuals on six days and six nights during five tracking sessions from March to November 2004. In addition, five stationary data-logging receivers, moored at specific locations from the mouth to the top of the estuary provided additional long-term monitoring. Kernel home ranges (95% UD) varied in size (26 296-165 321m²) but were all located in a common high use area situated between 300-1 300m from the estuary mouth, which coincided with the highest abundance of prey items. There was no significant variation in home range size [C² (N = 9, df = 4) = 4.18; p = 0.38] between the temporally segregated tracking sessions (over nine months). The persistence of these home range estimates were confirmed by the long-term data-logging receivers. There was no significant diel variation in home range size [F(4, 64) = 0.05, p = 0.99] or core area size [F(4, 64) = 1.40, p = 0.25]. Fish length showed negative, although not significant, relationships between home range size (p = 0.225); number of home range areas (p = 0.065); core area size (p = 0.512) and home range length (p = 0.320). Use of habitat and home range dynamics of spotted grunter in the East Kleinemonde Estuary were consistent over the nine month study period, and they appeared to be influenced more by biotic than abiotic factors. However, when the mouth opened at the end of the study, most tagged fish vacated their home ranges and emigrated to sea.
- Full Text:
- Date Issued: 2008
- Authors: O'Connell, Bronwyn Anne
- Date: 2008
- Subjects: Grunts (Fishes) -- South Africa -- Eastern Cape , Pomadasys -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fishes -- Home range , Fishes -- Home range -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5286 , http://hdl.handle.net/10962/d1005130 , Grunts (Fishes) -- South Africa -- Eastern Cape , Pomadasys -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine fishes -- Habitat -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fishes -- Home range , Fishes -- Home range -- South Africa -- Eastern Cape
- Description: The spotted grunter (Pomadasys commersonnii) is an important, estuarine-dependent, fishery species in southern Africa. Since estuaries are essential habitats in the life history of this species, the quantification of area use patterns and movements is important for fisheries management. In this study, acoustic telemetry was used to investigate movements, use of habitat and home range dynamics of spotted grunter in the small intermittently open East Kleinemonde Estuary on the Eastern Cape coast of South Africa. Nine spotted grunter (range: 326-489mm TL) were surgically equipped with uniquely coded acoustic transmitters. Positional fixes were obtained by manual tracking tagged individuals on six days and six nights during five tracking sessions from March to November 2004. In addition, five stationary data-logging receivers, moored at specific locations from the mouth to the top of the estuary provided additional long-term monitoring. Kernel home ranges (95% UD) varied in size (26 296-165 321m²) but were all located in a common high use area situated between 300-1 300m from the estuary mouth, which coincided with the highest abundance of prey items. There was no significant variation in home range size [C² (N = 9, df = 4) = 4.18; p = 0.38] between the temporally segregated tracking sessions (over nine months). The persistence of these home range estimates were confirmed by the long-term data-logging receivers. There was no significant diel variation in home range size [F(4, 64) = 0.05, p = 0.99] or core area size [F(4, 64) = 1.40, p = 0.25]. Fish length showed negative, although not significant, relationships between home range size (p = 0.225); number of home range areas (p = 0.065); core area size (p = 0.512) and home range length (p = 0.320). Use of habitat and home range dynamics of spotted grunter in the East Kleinemonde Estuary were consistent over the nine month study period, and they appeared to be influenced more by biotic than abiotic factors. However, when the mouth opened at the end of the study, most tagged fish vacated their home ranges and emigrated to sea.
- Full Text:
- Date Issued: 2008
Ichthyofaunal characteristics of a typical temporarily open/closed estuary on the southeast coast of South Africa
- Cowley, Paul D, Heemstra, Phillip C
- Authors: Cowley, Paul D , Heemstra, Phillip C
- Date: 2001
- Subjects: Estuarine fishes -- Ecology -- Indian Ocean , Estuarine ecology -- South Africa , Fish communities -- South Africa , Fish communities -- Indian Ocean
- Language: English
- Type: Text
- Identifier: vital:15021 , http://hdl.handle.net/10962/d1019862 , ISSN 0073-4381 , Ichthyological Bulletin J.L.B. Smith Institute of Ichthyology; No. 71
- Description: The present study was undertaken to describe the species composition, size composition and distribution of the fish fauna associated with the temporarily open/closed East Kleinemonde Estuary on the southeast coast of South Africa. Data collected on the estuary mouth condition from March 1993 to August 1997 indicated that this system was predominantly closed, while open mouth conditions were unseasonal and prevailed for only a short duration following periods of high rainfall. Fishes were sampled throughout the estuary between April 1993 and January 1997 using seine and gill nets. A total of 30 species belonging to 17 families were recorded, including the critically endangered estuarine pipefish Syngnathus watermeyeri. Besides the estuarine pipefish, an additional five species capable of completing their life cycle within the estuary were recorded. The ichthyofaunal community was dominated by 18 marine-spawning species with varying degrees of dependence on estuaries as nursery areas. The marine species that are not dependent on estuaries as nursery areas were represented by three species, while the euryhaline freshwater species, obligate catadromous species and facultative catadromous species were each represented by one species. The dominant members of the estuarine-spawning group were well represented by all post-larval life-history stages, whereas the mean size of each marine-spawning species indicated that juvenile size classes dominated this group. Classification and ordination of both the small- and large-mesh seine net fish assemblages revealed a high degree of similarity throughout the estuary, with the exception of a distinct grouping associated with sandy substrata in the lower reaches of the system. Catch per unit effort (CPUE) data provided evidence of spatial segregation by several species as well as within some families (e.g. Gobiidae). , Rhodes University Libraries (Digitisation)
- Full Text:
- Date Issued: 2001
- Authors: Cowley, Paul D , Heemstra, Phillip C
- Date: 2001
- Subjects: Estuarine fishes -- Ecology -- Indian Ocean , Estuarine ecology -- South Africa , Fish communities -- South Africa , Fish communities -- Indian Ocean
- Language: English
- Type: Text
- Identifier: vital:15021 , http://hdl.handle.net/10962/d1019862 , ISSN 0073-4381 , Ichthyological Bulletin J.L.B. Smith Institute of Ichthyology; No. 71
- Description: The present study was undertaken to describe the species composition, size composition and distribution of the fish fauna associated with the temporarily open/closed East Kleinemonde Estuary on the southeast coast of South Africa. Data collected on the estuary mouth condition from March 1993 to August 1997 indicated that this system was predominantly closed, while open mouth conditions were unseasonal and prevailed for only a short duration following periods of high rainfall. Fishes were sampled throughout the estuary between April 1993 and January 1997 using seine and gill nets. A total of 30 species belonging to 17 families were recorded, including the critically endangered estuarine pipefish Syngnathus watermeyeri. Besides the estuarine pipefish, an additional five species capable of completing their life cycle within the estuary were recorded. The ichthyofaunal community was dominated by 18 marine-spawning species with varying degrees of dependence on estuaries as nursery areas. The marine species that are not dependent on estuaries as nursery areas were represented by three species, while the euryhaline freshwater species, obligate catadromous species and facultative catadromous species were each represented by one species. The dominant members of the estuarine-spawning group were well represented by all post-larval life-history stages, whereas the mean size of each marine-spawning species indicated that juvenile size classes dominated this group. Classification and ordination of both the small- and large-mesh seine net fish assemblages revealed a high degree of similarity throughout the estuary, with the exception of a distinct grouping associated with sandy substrata in the lower reaches of the system. Catch per unit effort (CPUE) data provided evidence of spatial segregation by several species as well as within some families (e.g. Gobiidae). , Rhodes University Libraries (Digitisation)
- Full Text:
- Date Issued: 2001
Coastal movements and estuarine use of sub-adult and adult leervis, lichia amia: results from long-term acoustic tracking
- Authors: Mxo, Rebecca Vuyolwethu
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422314 , vital:71930
- Description: Information on fish movement is important not only for understanding a species’ ecological importance, but also for developing appropriate conservation and management policies that are critical for food security and biodiversity preservation. This information is particularly important for species that occupy different habitats at different life history stages, and display predictable movement patterns, such as an annual spawning migration. Leervis Lichia amia is an estuary-dependent fishery species of high ecological and recreational importance in South Africa. There has been a steady decline in catch-per-unit-effort in the marine recreational fishery for this species over the past 20 years, and the most recent stock assessment classified the adult stock as collapsed. This study investigates L. amia multi-year coastal migrations and estuarine habitat use of sub-adult and adult fish tagged with long-life acoustic transmitters Seventy-eight L. amia (two juveniles, fifty-four subadults, and twenty-one adults) were tagged throughout their South African distribution and monitored between 2011 and 2020 producing a decade long dataset. Results show that regardless of the tagging region, clear migration patterns were observed, demonstrating that both sub-adult and adult L. amia migrate annually to KZN in the austral winter and predictably return to the WC and EC waters in the summer. The likelihood of partial migration was also identified, with the coexistence of migratory and resident behaviors within a single L. amia population. In addition, Overwintering behaviour was also observed with L. amia adults that remained resident throughout the year, foregoing the annual migration, phenomenon known as skipped spawning, and homing behaviour, where L. amia, particularly those tagged in the EC and WC, were recorded returning to previously occupied tagging locations and surrounding areas. The importance of estuaries to sub-adult and adult fish was also assessed and identified the importance of estuaries not only to subadults but also to adults. Estuary visits were strongly influenced by the environment which the fish was tagged in, temporal and seasonal changes, and life-history stages. The predictability of their migrations (almost to the day), the varied migratory behaviour (overwintering), returning to sites of familiarity post-migration, and long-term dependency on estuaries even as sub-adults and adults, provide motivation for increased protection of this species, including extending the network of estuarine protected areas in the country, and a closed fishing season, particularly during the annual winter migration. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-29
- Authors: Mxo, Rebecca Vuyolwethu
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422314 , vital:71930
- Description: Information on fish movement is important not only for understanding a species’ ecological importance, but also for developing appropriate conservation and management policies that are critical for food security and biodiversity preservation. This information is particularly important for species that occupy different habitats at different life history stages, and display predictable movement patterns, such as an annual spawning migration. Leervis Lichia amia is an estuary-dependent fishery species of high ecological and recreational importance in South Africa. There has been a steady decline in catch-per-unit-effort in the marine recreational fishery for this species over the past 20 years, and the most recent stock assessment classified the adult stock as collapsed. This study investigates L. amia multi-year coastal migrations and estuarine habitat use of sub-adult and adult fish tagged with long-life acoustic transmitters Seventy-eight L. amia (two juveniles, fifty-four subadults, and twenty-one adults) were tagged throughout their South African distribution and monitored between 2011 and 2020 producing a decade long dataset. Results show that regardless of the tagging region, clear migration patterns were observed, demonstrating that both sub-adult and adult L. amia migrate annually to KZN in the austral winter and predictably return to the WC and EC waters in the summer. The likelihood of partial migration was also identified, with the coexistence of migratory and resident behaviors within a single L. amia population. In addition, Overwintering behaviour was also observed with L. amia adults that remained resident throughout the year, foregoing the annual migration, phenomenon known as skipped spawning, and homing behaviour, where L. amia, particularly those tagged in the EC and WC, were recorded returning to previously occupied tagging locations and surrounding areas. The importance of estuaries to sub-adult and adult fish was also assessed and identified the importance of estuaries not only to subadults but also to adults. Estuary visits were strongly influenced by the environment which the fish was tagged in, temporal and seasonal changes, and life-history stages. The predictability of their migrations (almost to the day), the varied migratory behaviour (overwintering), returning to sites of familiarity post-migration, and long-term dependency on estuaries even as sub-adults and adults, provide motivation for increased protection of this species, including extending the network of estuarine protected areas in the country, and a closed fishing season, particularly during the annual winter migration. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-29
Movement patterns and population dynamics of four catsharks endemic to South Africa
- Authors: Escobar-Porras, Jessica
- Date: 2010
- Subjects: Chondrichthyes -- South Africa , Fish populations -- South Africa , Fishes -- Behavior -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5303 , http://hdl.handle.net/10962/d1005148 , Chondrichthyes -- South Africa , Fish populations -- South Africa , Fishes -- Behavior -- South Africa
- Description: Sharks are particularly vulnerable to over-exploitation. Although catsharks are an important component of the near-shore marine biodiversity in South Africa and most of the species are endemic, little is known about their movement patterns, home range and population size. With an increasing number of recreational fishers this information is crucial for their conservation. The aims of this study were threefold. Firstly, to identify and analyze existing data sources on movement patterns and population dynamics for four catshark species: pyjama (Poroderma africanum), leopard (P. pantherinum), puffadder (Haploblepharus edwarsii) and brown (H. fuscus). This highlighted a number of shortcomings with existing data sets, largely because these studies had diverse objectives and were not aimed solely at catsharks. Secondly, a dedicated study was carried out for a limited area, testing a number of methods for data collection, and where appropriate the data was analyzed to determine movement patterns and population numbers. Thirdly, the most appropriate methodology for future studies (with similar objectives) was identified, and the results of the study were used to propose a number of conservation measures. All species of catsharks exhibited strong site fidelity and limited dispersal for extended periods. A few individuals did, however, travel distances in excess of 150 km. Significant trends in temporal abundance were not observed, nevertheless, there was some evidence for higher catches from September to December. Population estimates for the study area were low, with P. africanum having the smallest population size while H. fuscus had the highest population size within the restricted study area. Limited movements, high site fidelity and small population sizes emphasize their vulnerability and suggest that catsharks would benefit from no-take marine protected areas.
- Full Text:
- Date Issued: 2010
- Authors: Escobar-Porras, Jessica
- Date: 2010
- Subjects: Chondrichthyes -- South Africa , Fish populations -- South Africa , Fishes -- Behavior -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5303 , http://hdl.handle.net/10962/d1005148 , Chondrichthyes -- South Africa , Fish populations -- South Africa , Fishes -- Behavior -- South Africa
- Description: Sharks are particularly vulnerable to over-exploitation. Although catsharks are an important component of the near-shore marine biodiversity in South Africa and most of the species are endemic, little is known about their movement patterns, home range and population size. With an increasing number of recreational fishers this information is crucial for their conservation. The aims of this study were threefold. Firstly, to identify and analyze existing data sources on movement patterns and population dynamics for four catshark species: pyjama (Poroderma africanum), leopard (P. pantherinum), puffadder (Haploblepharus edwarsii) and brown (H. fuscus). This highlighted a number of shortcomings with existing data sets, largely because these studies had diverse objectives and were not aimed solely at catsharks. Secondly, a dedicated study was carried out for a limited area, testing a number of methods for data collection, and where appropriate the data was analyzed to determine movement patterns and population numbers. Thirdly, the most appropriate methodology for future studies (with similar objectives) was identified, and the results of the study were used to propose a number of conservation measures. All species of catsharks exhibited strong site fidelity and limited dispersal for extended periods. A few individuals did, however, travel distances in excess of 150 km. Significant trends in temporal abundance were not observed, nevertheless, there was some evidence for higher catches from September to December. Population estimates for the study area were low, with P. africanum having the smallest population size while H. fuscus had the highest population size within the restricted study area. Limited movements, high site fidelity and small population sizes emphasize their vulnerability and suggest that catsharks would benefit from no-take marine protected areas.
- Full Text:
- Date Issued: 2010
Rhodes University Research Report 2015
- Rhodes University, Gillitt, Tarryn, Goba, Busi, Macgregor, Jill, Roberts, Jaine, Dore, Sally
- Authors: Rhodes University , Gillitt, Tarryn , Goba, Busi , Macgregor, Jill , Roberts, Jaine , Dore, Sally
- Date: 2015
- Language: English
- Type: Text
- Identifier: http://hdl.handle.net/10962/59298 , vital:27546
- Description: From Foreword by Dr Sizwe Mabizela: A further feature of research at Rhodes University has long been international collaborations, many of them responsible for raising the international competitiveness and voice of scholarship involving Rhodes academics and students. In March 2015, Rhodes University became a founder member of the African Research Universities’ Alliance (ARUA), launched at the African Higher Education Summit in Senegal. Leading universities with strong programmes of research and Postgraduate training formed the network of 16 institutions, which aim to bring together intersecting and complementary strengths in the interest of building critical mass in the key development priorities of the African continent. , A publication of the Rhodes University Research Office, compiled and edited by Tarryn Gillitt, Busi Goba, Patricia Jacob, Jill Macgregor and Jaine Roberts. Design & Layout: Sally Dore.
- Full Text:
- Date Issued: 2015
- Authors: Rhodes University , Gillitt, Tarryn , Goba, Busi , Macgregor, Jill , Roberts, Jaine , Dore, Sally
- Date: 2015
- Language: English
- Type: Text
- Identifier: http://hdl.handle.net/10962/59298 , vital:27546
- Description: From Foreword by Dr Sizwe Mabizela: A further feature of research at Rhodes University has long been international collaborations, many of them responsible for raising the international competitiveness and voice of scholarship involving Rhodes academics and students. In March 2015, Rhodes University became a founder member of the African Research Universities’ Alliance (ARUA), launched at the African Higher Education Summit in Senegal. Leading universities with strong programmes of research and Postgraduate training formed the network of 16 institutions, which aim to bring together intersecting and complementary strengths in the interest of building critical mass in the key development priorities of the African continent. , A publication of the Rhodes University Research Office, compiled and edited by Tarryn Gillitt, Busi Goba, Patricia Jacob, Jill Macgregor and Jaine Roberts. Design & Layout: Sally Dore.
- Full Text:
- Date Issued: 2015
Habitat use of important juvenile fish species in temperate Earnestine nursery areas with notes on feeding ecology and historical shifts to assist with conservation planning, South Africa
- Authors: Nel, Larize
- Date: 2018
- Subjects: Mariculture -- South Africa , Fishes -- Ecology -- South Africa Fishes -- Food -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32904 , vital:32396
- Description: Estuaries are among the most productive ecosystems worldwide as they provide important refuge and feeding areas for the juveniles of many marine species, many of which have recreational importance. The use of these nursery areas by juvenile fishes in South Africa are in need of further investigation and many critical areas such as shallow water creeks and vegetated habitats remain understudied. By using mixed-methods, estuarine fish assemblages were assessed in five permanently open estuaries in the Eastern Cape Province of South Africa. A total of 81 428 comprising 24 families and 40 species of fishes were sampled by means of a 50 m seine net (12 mm mesh) along the length of these systems that comprised of six equidistant sites during the summer recruitment period (October - December) of 2014 and 2015. A higher catch per unit effort (CPUE) was recorded in 2014 (68 875) compared to the following year where a decline of approximately 82% was observed in the catch (12 553) for all estuaries except the Kromme Estuary. Catches were mainly dominated by the marine estuarine dependent sparid, Rhabdosargus holubi and the solely estuarine clupeid, Gilchristella aestuaria. Species compositions and catch abundance with regards to historical catches showed that the abundance of many marine estuarine dependent juveniles as well as important recreational species have declined within these systems and are mainly attributed to marine overfishing and the exploitation of undersized individuals in estuarine nurseries. Juvenile fishes that occur in these estuaries utilize a range of vegetated habitats ranging from salt marsh creeks, Zostera capensis beds, Spartina maritima and previously unexplored Phragmites australis areas. Sampling was achieved by using passive, double-winged, six-hooped fyke nets, 1 mm mesh size that was secured in placed on the nocturnal flood tide at each inundated vegetated and adjacent unvegetated habitat types. Higher catches were frequently recorded in vegetated areas for solely estuarine and marine estuarine dependent species and supports evidence of plasticity within these habitats. In general, the previously unstudied reed, P. australis showed the highest species richness and abundance of juvenile fishes overall, followed by, Z. capensis and the intertidal salt marsh species, S. maritima. These findings relate to many international trends on the value of vegetated areas as refugia for young fishes in estuaries. Fishes were also showing evidence of feeding and sheltering in these areas. By using conventional stomach contents and stable isotope methods (δ13C and δ15N signatures) on the abundant R. holubi in previously selected vegetation sites, it was clear that this species has a significant reliance on any of these habitats as their diets was largely comprised of a mixture of epiphytic algae and aquatic macrophytes. In addition, the diet of larger individuals (>80 mm) showed a greater component of invertebrates in previously unexplored habitats, which proves their omnivorous diet related to ontogenetic niche use. Knowledge of fine-scale habitat use by fishes is essential for conservation planning as exclusion zones can be optimised to limit anthropogenic influence on nursery use patterns in fishes. The availability of shallow water habitats (<60 cm) was assessed as an additional driver to explain the species diversity and richness of juvenile fishes within the lower reaches. These habitats are known as important nursery habitats providing numerous marine and estuarine spawned fishes with adequate refuge and food supply. This shallow water volume was measured by means of a two-man kayak using both the spring high and low tides in the lower reaches of these systems to assess juvenile assemblages. It was clear from the results that aquatic vegetation significantly adds to the volume of these areas and as a result, much greater fish density and species richness were observed. Generalized additive models showed that marine spawned species were particularly reliant on the availability of this shallow water along with submerged vegetation and additional environmental variables. The presence of structurally submerged vegetation typically characterized within shallow estuarine waters is commonly believed to reduce predation risk resulting in elevated densities of biota. Based on the current stock status and percentage of pristine breeding stock, five fish species classified as collapsed/overexploited was consistently found within these systems with an additional 14 species currently classified as exploited/vulnerable. Based on the current species richness and diversity, available habitat cover and knowledge regarding important recreational species, priority areas that require some form of legal protection in order to meet potential biodiversity targets, could be identified. It is a legal requirement in South Africa that all estuaries require management plans that should be based on good knowledge of priority habitats for fauna and flora. The identification of estuarine protected areas is seen as a mechanism for protecting a representative sample of the biodiversity accompanied by a complete range of environmental gradients and habitat types at a reasonable scale in order to maximize the protection of estuarine species.
- Full Text:
- Date Issued: 2018
- Authors: Nel, Larize
- Date: 2018
- Subjects: Mariculture -- South Africa , Fishes -- Ecology -- South Africa Fishes -- Food -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32904 , vital:32396
- Description: Estuaries are among the most productive ecosystems worldwide as they provide important refuge and feeding areas for the juveniles of many marine species, many of which have recreational importance. The use of these nursery areas by juvenile fishes in South Africa are in need of further investigation and many critical areas such as shallow water creeks and vegetated habitats remain understudied. By using mixed-methods, estuarine fish assemblages were assessed in five permanently open estuaries in the Eastern Cape Province of South Africa. A total of 81 428 comprising 24 families and 40 species of fishes were sampled by means of a 50 m seine net (12 mm mesh) along the length of these systems that comprised of six equidistant sites during the summer recruitment period (October - December) of 2014 and 2015. A higher catch per unit effort (CPUE) was recorded in 2014 (68 875) compared to the following year where a decline of approximately 82% was observed in the catch (12 553) for all estuaries except the Kromme Estuary. Catches were mainly dominated by the marine estuarine dependent sparid, Rhabdosargus holubi and the solely estuarine clupeid, Gilchristella aestuaria. Species compositions and catch abundance with regards to historical catches showed that the abundance of many marine estuarine dependent juveniles as well as important recreational species have declined within these systems and are mainly attributed to marine overfishing and the exploitation of undersized individuals in estuarine nurseries. Juvenile fishes that occur in these estuaries utilize a range of vegetated habitats ranging from salt marsh creeks, Zostera capensis beds, Spartina maritima and previously unexplored Phragmites australis areas. Sampling was achieved by using passive, double-winged, six-hooped fyke nets, 1 mm mesh size that was secured in placed on the nocturnal flood tide at each inundated vegetated and adjacent unvegetated habitat types. Higher catches were frequently recorded in vegetated areas for solely estuarine and marine estuarine dependent species and supports evidence of plasticity within these habitats. In general, the previously unstudied reed, P. australis showed the highest species richness and abundance of juvenile fishes overall, followed by, Z. capensis and the intertidal salt marsh species, S. maritima. These findings relate to many international trends on the value of vegetated areas as refugia for young fishes in estuaries. Fishes were also showing evidence of feeding and sheltering in these areas. By using conventional stomach contents and stable isotope methods (δ13C and δ15N signatures) on the abundant R. holubi in previously selected vegetation sites, it was clear that this species has a significant reliance on any of these habitats as their diets was largely comprised of a mixture of epiphytic algae and aquatic macrophytes. In addition, the diet of larger individuals (>80 mm) showed a greater component of invertebrates in previously unexplored habitats, which proves their omnivorous diet related to ontogenetic niche use. Knowledge of fine-scale habitat use by fishes is essential for conservation planning as exclusion zones can be optimised to limit anthropogenic influence on nursery use patterns in fishes. The availability of shallow water habitats (<60 cm) was assessed as an additional driver to explain the species diversity and richness of juvenile fishes within the lower reaches. These habitats are known as important nursery habitats providing numerous marine and estuarine spawned fishes with adequate refuge and food supply. This shallow water volume was measured by means of a two-man kayak using both the spring high and low tides in the lower reaches of these systems to assess juvenile assemblages. It was clear from the results that aquatic vegetation significantly adds to the volume of these areas and as a result, much greater fish density and species richness were observed. Generalized additive models showed that marine spawned species were particularly reliant on the availability of this shallow water along with submerged vegetation and additional environmental variables. The presence of structurally submerged vegetation typically characterized within shallow estuarine waters is commonly believed to reduce predation risk resulting in elevated densities of biota. Based on the current stock status and percentage of pristine breeding stock, five fish species classified as collapsed/overexploited was consistently found within these systems with an additional 14 species currently classified as exploited/vulnerable. Based on the current species richness and diversity, available habitat cover and knowledge regarding important recreational species, priority areas that require some form of legal protection in order to meet potential biodiversity targets, could be identified. It is a legal requirement in South Africa that all estuaries require management plans that should be based on good knowledge of priority habitats for fauna and flora. The identification of estuarine protected areas is seen as a mechanism for protecting a representative sample of the biodiversity accompanied by a complete range of environmental gradients and habitat types at a reasonable scale in order to maximize the protection of estuarine species.
- Full Text:
- Date Issued: 2018
Superstition, atheism and reasonable faith in Acts 26: a Graeco-Roman perspective on Paul’s defence before Festus and Agrippa
- Authors: Germiquet, Edouard Ariste
- Date: 2001
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21065 , http://hdl.handle.net/10962/6224
- Description: This thesis investigates Luke‟s presentation of Paul‟s final and climactic defence of the gospel which takes place before Festus and King Agrippa II (Ac.26). It indicates how Luke has made use of the philosophical doctrine of the mean in order to present Christianity as a reasonable and rational faith. This investigation explores how Luke creates a literary framework within which to promote Paul as reasonable and rational through the application of the topos that true piety is the mean between the two extremes of superstition and atheism. The thesis is therefore structured around three dominant sections in which the major themes of superstition, atheism and rational faith are treated independently. Each section consists of an analysis of Luke‟s choice of words and his description of the behavioural patterns of each representative group so that a consistent picture progressively emerges in support of the basic framework. At all stages of the investigation, reference is made to contemporary moral philosophers, Hellenistic Judaism and the early Christian apologists so that the language, literary settings and stereotypes used by Luke can be clearly defined. This not only clarifies the text of Acts 26 but contributes to an overall appreciation of Luke‟s literary technique. At all points in the development of the thesis, the relevance and centrality which the resurrection has for Luke is kept in mind. This not only acts as a backdrop in understanding Luke‟s depiction of the superstitious and the atheist but is crucial in grasping Luke‟s presentation of Christianity as a rational faith. The thesis is brought to a close by a discussion on Luke's intended audience and the significance of his dedication to Theophilus.
- Full Text:
- Date Issued: 2001
- Authors: Germiquet, Edouard Ariste
- Date: 2001
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21065 , http://hdl.handle.net/10962/6224
- Description: This thesis investigates Luke‟s presentation of Paul‟s final and climactic defence of the gospel which takes place before Festus and King Agrippa II (Ac.26). It indicates how Luke has made use of the philosophical doctrine of the mean in order to present Christianity as a reasonable and rational faith. This investigation explores how Luke creates a literary framework within which to promote Paul as reasonable and rational through the application of the topos that true piety is the mean between the two extremes of superstition and atheism. The thesis is therefore structured around three dominant sections in which the major themes of superstition, atheism and rational faith are treated independently. Each section consists of an analysis of Luke‟s choice of words and his description of the behavioural patterns of each representative group so that a consistent picture progressively emerges in support of the basic framework. At all stages of the investigation, reference is made to contemporary moral philosophers, Hellenistic Judaism and the early Christian apologists so that the language, literary settings and stereotypes used by Luke can be clearly defined. This not only clarifies the text of Acts 26 but contributes to an overall appreciation of Luke‟s literary technique. At all points in the development of the thesis, the relevance and centrality which the resurrection has for Luke is kept in mind. This not only acts as a backdrop in understanding Luke‟s depiction of the superstitious and the atheist but is crucial in grasping Luke‟s presentation of Christianity as a rational faith. The thesis is brought to a close by a discussion on Luke's intended audience and the significance of his dedication to Theophilus.
- Full Text:
- Date Issued: 2001
Persuasuve conflict: an hermeneutical model for interpreting Galatians in the context of the South African church
- Authors: Holgate, David A
- Date: 1990
- Subjects: Bible. Galatians -- Criticism, Textual , Liberation theology -- South Africa
- Language: English
- Type: Thesis , Masters , MTh
- Identifier: vital:1213 , http://hdl.handle.net/10962/d1001542
- Description: This study looks at how to interpret Paul's letter to the Galatians in the contemporary South African church. It aims to provide a Bible study method for doing this which accounts both for the context in which interpretation takes place and for the requirements of exegesis. To this end, use is made of a combination of contextual Bible study methods and a recent multidimensional exegetical model, all of which are currently employed in South Africa. Initially, the study surveys a range of recent critical approaches to the Pauline epistles, particularly as these are employed by South African scholars working on Galatians. The fact that different exegetical approaches focus on different dimensions of the text, reveals the usefulness of a multidimensional exegetical model. The multidimensional exegetical model of Rousseau, which functions within a communication paradigm, is then introduced as an exegetical guide. To meet the second requirement of this study, the question of contextual exegesis is examined. Particular use is made of the hermeneutical approach of liberation theology, with its three mediations of social analysis, theological reflection and practical implementation. The central part of this study explores the implications of contextual interpretation and multidimensional exegesis of Galatians. The pre-canonical, canonical and contemporary contexts which affect the understanding of Galatians are discussed, and the multidimensional exegetical model is used to introduce the Galatian letter as a whole. The last part deals with the practical questions of group Bible study. The exegetical and hermeneutical theory developed earlier is simplified to provide a contextual Bible study method and this method is applied to three pericopes from Galatians. The task of bridging the gap between the university and the church is not an easy one, nor one which is solved by a single Bible study method. The exegetical and hermeneutical questions raised here point to the need for ongoing interaction between South African community of biblical scholars and those involved in the everyday life of the South African church
- Full Text:
- Date Issued: 1990
- Authors: Holgate, David A
- Date: 1990
- Subjects: Bible. Galatians -- Criticism, Textual , Liberation theology -- South Africa
- Language: English
- Type: Thesis , Masters , MTh
- Identifier: vital:1213 , http://hdl.handle.net/10962/d1001542
- Description: This study looks at how to interpret Paul's letter to the Galatians in the contemporary South African church. It aims to provide a Bible study method for doing this which accounts both for the context in which interpretation takes place and for the requirements of exegesis. To this end, use is made of a combination of contextual Bible study methods and a recent multidimensional exegetical model, all of which are currently employed in South Africa. Initially, the study surveys a range of recent critical approaches to the Pauline epistles, particularly as these are employed by South African scholars working on Galatians. The fact that different exegetical approaches focus on different dimensions of the text, reveals the usefulness of a multidimensional exegetical model. The multidimensional exegetical model of Rousseau, which functions within a communication paradigm, is then introduced as an exegetical guide. To meet the second requirement of this study, the question of contextual exegesis is examined. Particular use is made of the hermeneutical approach of liberation theology, with its three mediations of social analysis, theological reflection and practical implementation. The central part of this study explores the implications of contextual interpretation and multidimensional exegesis of Galatians. The pre-canonical, canonical and contemporary contexts which affect the understanding of Galatians are discussed, and the multidimensional exegetical model is used to introduce the Galatian letter as a whole. The last part deals with the practical questions of group Bible study. The exegetical and hermeneutical theory developed earlier is simplified to provide a contextual Bible study method and this method is applied to three pericopes from Galatians. The task of bridging the gap between the university and the church is not an easy one, nor one which is solved by a single Bible study method. The exegetical and hermeneutical questions raised here point to the need for ongoing interaction between South African community of biblical scholars and those involved in the everyday life of the South African church
- Full Text:
- Date Issued: 1990
The biology and movement patterns of non-native common carp, cyprinus carpio (l) in Groenvlei, South Africa
- Authors: Mukhari, Dinah Lorraine
- Date: 2022-04-06
- Subjects: Carp South Africa Goukamma Nature Reserve , Introduced fishes South Africa Goukamma Nature Reserve , Carp Behavior South Africa Goukamma Nature Reserve , Carp South Africa Goukamma Nature Reserve Growth , Carp Habitat South Africa Goukamma Nature Reserve , Carp South Africa Goukamma Nature Reserve Reproduction , Habitat conservation South Africa Goukamma Nature Reserve , Aquatic resources conservation South Africa Goukamma Nature Reserve
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/291233 , vital:56834
- Description: The common carp, Cyprinus carpio is a highly invasive fish species, first introduced into South Africa in the late nineteen century, and now widely spread throughout the country. In 1991 carp were illegally introduced to Groenvlei, within the Goukamma Nature Reserve in the Western Cape Province. Decreases in water quality and declines in biota have been attributed to the now large numbers of carp. Management measures have commenced to reduce the carp population, however these are not underpinned by science as little is known about the biology and movement patterns of resident carp. The age, growth and maturity of carp within the lake was determined using oxytetracycline hydrochloride marked asteriscus otoliths and macroscopic gonad development staging methods. The results showed that carp in Groenvlei had similar growth characteristics to the invasive populations in North America and Australia; fast growth during the first three to five years and reproductive maturity attained between the ages of two to three years, and are long lived (maximum age of 20 years old). Their growth however differed from the only other study on a South African population. Six acoustically tagged carp were manually tracked in order to report on their movement patterns and habitat use. Carp moved much greater distances in February compared to October and November, and occupied different areas of the lake. In November they were found to aggregate in backwaters which corresponds with their breeding activities. Literature on global carp control shows that whilst eradication of this fish can be achieved in small isolated waters using icthyocides and water drawdowns, in conservation priority areas such as Groenvlei where this is not possible, mechanical removal using multiple gears targeting vulnerable life stages can most efficient at controlling carp. This study identified where and when these methods could be focused to optimise control efforts. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-04-06
- Authors: Mukhari, Dinah Lorraine
- Date: 2022-04-06
- Subjects: Carp South Africa Goukamma Nature Reserve , Introduced fishes South Africa Goukamma Nature Reserve , Carp Behavior South Africa Goukamma Nature Reserve , Carp South Africa Goukamma Nature Reserve Growth , Carp Habitat South Africa Goukamma Nature Reserve , Carp South Africa Goukamma Nature Reserve Reproduction , Habitat conservation South Africa Goukamma Nature Reserve , Aquatic resources conservation South Africa Goukamma Nature Reserve
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/291233 , vital:56834
- Description: The common carp, Cyprinus carpio is a highly invasive fish species, first introduced into South Africa in the late nineteen century, and now widely spread throughout the country. In 1991 carp were illegally introduced to Groenvlei, within the Goukamma Nature Reserve in the Western Cape Province. Decreases in water quality and declines in biota have been attributed to the now large numbers of carp. Management measures have commenced to reduce the carp population, however these are not underpinned by science as little is known about the biology and movement patterns of resident carp. The age, growth and maturity of carp within the lake was determined using oxytetracycline hydrochloride marked asteriscus otoliths and macroscopic gonad development staging methods. The results showed that carp in Groenvlei had similar growth characteristics to the invasive populations in North America and Australia; fast growth during the first three to five years and reproductive maturity attained between the ages of two to three years, and are long lived (maximum age of 20 years old). Their growth however differed from the only other study on a South African population. Six acoustically tagged carp were manually tracked in order to report on their movement patterns and habitat use. Carp moved much greater distances in February compared to October and November, and occupied different areas of the lake. In November they were found to aggregate in backwaters which corresponds with their breeding activities. Literature on global carp control shows that whilst eradication of this fish can be achieved in small isolated waters using icthyocides and water drawdowns, in conservation priority areas such as Groenvlei where this is not possible, mechanical removal using multiple gears targeting vulnerable life stages can most efficient at controlling carp. This study identified where and when these methods could be focused to optimise control efforts. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-04-06
Factors influencing estuarine and coastal connectivity of an estuarine-dependent fishery species, Pomadasys commersonnii (Haemulidae)
- Authors: Dames, Michael Henri
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62307 , vital:28153
- Description: Expected release date-April 2019
- Full Text:
- Date Issued: 2018
- Authors: Dames, Michael Henri
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62307 , vital:28153
- Description: Expected release date-April 2019
- Full Text:
- Date Issued: 2018
Movement of coastal fishery species in Southern Africa: research trends, characterisation of behaviours and a case study on fishery implications
- Authors: Maggs, Jade Quinton
- Date: 2018
- Subjects: Fishery management -- Africa, Southern , Fisheries -- Africa, Southern , Fisheries -- Catch effort , Fisheries -- Environmental aspects , Fisheries --Monitoring , Biotelemetry , Sustainable fisheries -- Africa, Southern , Overfishing -- Africa, Southern
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/60574 , vital:27798
- Description: Movement of fishes is an integral part of their daily life, but has significant implications for fishery management. As with nearly all coastal countries, South Africa relies on coastal fisheries as a renewable resource, but many stocks have been overexploited for decades. Although it has long been recognised that an understanding of fish movement is necessary for effective management, it is with some difficulty that the subject has been studied in the past. In recent years, however, improvements in technology have provided the means for more in-depth investigations into fish movement. This research has revealed a range of complex movement behaviours. Movement in fishes occurs on a variety of temporal and spatial scales leading to the characteristic patterns of distribution and abundance observed in marine ecosystems. Fishes move nearly constantly in search of food, shelter or reproductive opportunities. Observations of behaviours such as long-term site fidelity, longdistance migration and natal homing are enabling ecologists to understand patterns of distribution and abundance within a species' range. Fish movement around the South African coast has been studied on numerous occasions but this has largely been confined to studies on single species. Movement behaviour of multiple species has been studied, but this has been limited to spatially localised marine protected area research. There has been little attempt in southern Africa to synthesize interspecific movement behaviour over wide spatial scales.Unprecedented concern over the biological effects of overexploitation, together with rapid technological advances in biotelemetry, have provided the impetus for much research, on a global scale, into the movement of marine animals. I reviewed 101 marine and estuarine fish movement studies from southern Africa, published from 1928 to 2014, with the aim of synthesising research trends and findings. Trends showed an increasing emphasis on fish movement research in publications in the sub-tropical and warm-temperate biogeographic regions along the south and east coasts of southern Africa. Although 63% of publications featured only marine studies, research into fine-scale habitat use in estuaries has been on the increase, concomitant with increasing accessibility of biotelemetry. Overall, 26 fish families were identified in the surveyed literature with regionally endemic sparids featuring in 32% of the publications. Ten movement themes were identified in the surveyed literature, including broad-scale movement patterns, which featured in 68% of studies, followed by fine- scale habitat usage (33%) and protected areas (26%). The most prominent phenomenon, emerging from this research, is that of partial migration, which describes the occurrence of resident and migratory behaviour within a coexisting animal population. Substantial progress has also been made in unravelling the complexities of fine-scale movements in marine reserves and habitat usage in estuaries. While this knowledge has enabled more effective management of South Africa's multi-user, multi-species fisheries, focus should now be directed at improving our understanding of the commonalities in movement behaviour, the associated driving forces behind this behaviour and the extent of movement across reserve boundaries. Mark-recapture data, collected over the past 30 years by the Oceanographic Research Institute’s Cooperative Fish Tagging Project (ORICFTP), were used to investigate broad- scale movement patterns of 30 prominent coastal fishery species (Chapter 4). Fishes were tagged with plastic dart tags along the coastline of southern Africa from Angola to Mozambique. This exercise yielded more than 10000 recaptures. The 30 chosen species represented 14 families, although 12 species belonged to a single family (Sparidae). Overall, 67% of recaptures were reported from the original tagging locality and 73% were recorded within 5 km of the tagging locality. The remaining observations extended from 6-3000 km. Movements were assigned to four distance bins (0-5 km, 6-50km, 51-500km and >500 km) and modelled with an ordinal logistic regression. Species, life-stage (juvenile/adult) and time- at-liberty were included as predictor variables. Model coefficients were then included in a cluster analysis, which produced two primary groupings of species (Category I and II), with two sub-groupings (Category IIa and IIb). Category I species were characterised by wide-ranging movements, greatest median recapture length and highest trophic levels. Category II species were characterised by residency, lower median recapture length and lower trophic levels. These findings have implications for fisheries management. Exploitation of resident species may lead to localised depletion, but their diffuse spatial distribution may offer some resilience. In contrast, even localised targeting of migratory species may pose a population level risk if individuals are known to aggregate. Life-cycle diversity or intra-population variability describes the existence of alternative strategies or tactics among coexisting individuals within an animal population (Chapter 5). Partial migration is a specific case of life-cycle diversity where coexisting groups exhibit either resident or migratory (wide-ranging) behaviour within a single population. Mark- recapture data collected under the auspices of the ORICFTP were used to investigate the occurrence and nature of life-cycle diversity in the movement behaviour of five non- diadromous fish species around the coastline of southern Africa. Among the five species were three teleosts (Category I and IIa) and two elasmobranchs (Category I). A fish was considered to have remained resident if recaptured within 0-5 km after 365 days at liberty. A fish was considered to have undertaken a wide-ranging movement if recaptured more than 50 km away from the release site in 365 days or less. A total of 1848 individuals from the five study species were recaptured during the study, of which 73% of the observations were classified as being resident. Binomial logistic regression confirmed that species, life-stage (juvenile/adult) and ecoregion were significant (p < 0.001) predictors of the probability of wide-ranging behaviour. A Gaussian model confirmed that species and ecoregion were also significant (p < 0.001) predictors of direction and distance of wide-ranging movement. However, the direction and distance of wide-ranging movements in juveniles did not differ significantly (p > 0.05) to that of adults. The median growth rate was mostly greater in wide- ranging individuals; however, this was only statistically significant (p < 0.05) in two cases. These findings provide unequivocal evidence of life-cycle diversity in five fish species, with vastly different life-histories. This ecological phenomenon may provide species resilience at the population level and needs to be considered in fisheries management initiatives. The movement of fishes is a fundamental aspect to consider when designing fishery management regimes. Unfortunately, traditional management strategies have often disregarded movement behaviour to the detriment of fish populations (Chapter 6). As a case study, the management of Lichia amia (Category I: wide-ranging) was evaluated in the context of its movement behaviour. Long-term catch-per-unit-effort (CPUE) datasets were examined for three South African recreational fishery sectors. The CPUE was standardised using generalized linear models (delta-Gamma/hurdle approach) to reduce the effect of factors other than abundance. Factors that were available for this purpose were year, month and locality/zone. Year was included in every model as the primary objective was to detect trends in abundance over time. Although standardised CPUE for all sectors showed an overall long-term decline, there was considerable variability in trends between the different recreational sectors and between datasets. Contrasting trends between competitive shore angling and general shore angling datasets were ascribed to hyperstability in competitive CPUE data. Hyperstability in this case was mostly influenced by rapidly improving technology, techniques and communication networks amongst competitive anglers. Month and locality were significant factors explaining the probability of catching L. amia. This suggests that the predictable aggregatory behaviour of this species could further compound the observed CPUE hyperstability. Although the CPUE responded positively for six years after implementation of the first minimum size and bag limits, and for one year after the decommercialisation of the species, these regulations and their amendments failed to arrest a long-term decline in the CPUE despite the ample evidence for hyperstability. It is clear from this case study that the predictable nature of wide-ranging behaviour in L. amia has made the population vulnerable to exploitation. This has led to the demise in the population, which could have been worse if not for the occurrence of intra-population variability in its movement behaviour, which may provide some measure of resilience.
- Full Text:
- Date Issued: 2018
- Authors: Maggs, Jade Quinton
- Date: 2018
- Subjects: Fishery management -- Africa, Southern , Fisheries -- Africa, Southern , Fisheries -- Catch effort , Fisheries -- Environmental aspects , Fisheries --Monitoring , Biotelemetry , Sustainable fisheries -- Africa, Southern , Overfishing -- Africa, Southern
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/60574 , vital:27798
- Description: Movement of fishes is an integral part of their daily life, but has significant implications for fishery management. As with nearly all coastal countries, South Africa relies on coastal fisheries as a renewable resource, but many stocks have been overexploited for decades. Although it has long been recognised that an understanding of fish movement is necessary for effective management, it is with some difficulty that the subject has been studied in the past. In recent years, however, improvements in technology have provided the means for more in-depth investigations into fish movement. This research has revealed a range of complex movement behaviours. Movement in fishes occurs on a variety of temporal and spatial scales leading to the characteristic patterns of distribution and abundance observed in marine ecosystems. Fishes move nearly constantly in search of food, shelter or reproductive opportunities. Observations of behaviours such as long-term site fidelity, longdistance migration and natal homing are enabling ecologists to understand patterns of distribution and abundance within a species' range. Fish movement around the South African coast has been studied on numerous occasions but this has largely been confined to studies on single species. Movement behaviour of multiple species has been studied, but this has been limited to spatially localised marine protected area research. There has been little attempt in southern Africa to synthesize interspecific movement behaviour over wide spatial scales.Unprecedented concern over the biological effects of overexploitation, together with rapid technological advances in biotelemetry, have provided the impetus for much research, on a global scale, into the movement of marine animals. I reviewed 101 marine and estuarine fish movement studies from southern Africa, published from 1928 to 2014, with the aim of synthesising research trends and findings. Trends showed an increasing emphasis on fish movement research in publications in the sub-tropical and warm-temperate biogeographic regions along the south and east coasts of southern Africa. Although 63% of publications featured only marine studies, research into fine-scale habitat use in estuaries has been on the increase, concomitant with increasing accessibility of biotelemetry. Overall, 26 fish families were identified in the surveyed literature with regionally endemic sparids featuring in 32% of the publications. Ten movement themes were identified in the surveyed literature, including broad-scale movement patterns, which featured in 68% of studies, followed by fine- scale habitat usage (33%) and protected areas (26%). The most prominent phenomenon, emerging from this research, is that of partial migration, which describes the occurrence of resident and migratory behaviour within a coexisting animal population. Substantial progress has also been made in unravelling the complexities of fine-scale movements in marine reserves and habitat usage in estuaries. While this knowledge has enabled more effective management of South Africa's multi-user, multi-species fisheries, focus should now be directed at improving our understanding of the commonalities in movement behaviour, the associated driving forces behind this behaviour and the extent of movement across reserve boundaries. Mark-recapture data, collected over the past 30 years by the Oceanographic Research Institute’s Cooperative Fish Tagging Project (ORICFTP), were used to investigate broad- scale movement patterns of 30 prominent coastal fishery species (Chapter 4). Fishes were tagged with plastic dart tags along the coastline of southern Africa from Angola to Mozambique. This exercise yielded more than 10000 recaptures. The 30 chosen species represented 14 families, although 12 species belonged to a single family (Sparidae). Overall, 67% of recaptures were reported from the original tagging locality and 73% were recorded within 5 km of the tagging locality. The remaining observations extended from 6-3000 km. Movements were assigned to four distance bins (0-5 km, 6-50km, 51-500km and >500 km) and modelled with an ordinal logistic regression. Species, life-stage (juvenile/adult) and time- at-liberty were included as predictor variables. Model coefficients were then included in a cluster analysis, which produced two primary groupings of species (Category I and II), with two sub-groupings (Category IIa and IIb). Category I species were characterised by wide-ranging movements, greatest median recapture length and highest trophic levels. Category II species were characterised by residency, lower median recapture length and lower trophic levels. These findings have implications for fisheries management. Exploitation of resident species may lead to localised depletion, but their diffuse spatial distribution may offer some resilience. In contrast, even localised targeting of migratory species may pose a population level risk if individuals are known to aggregate. Life-cycle diversity or intra-population variability describes the existence of alternative strategies or tactics among coexisting individuals within an animal population (Chapter 5). Partial migration is a specific case of life-cycle diversity where coexisting groups exhibit either resident or migratory (wide-ranging) behaviour within a single population. Mark- recapture data collected under the auspices of the ORICFTP were used to investigate the occurrence and nature of life-cycle diversity in the movement behaviour of five non- diadromous fish species around the coastline of southern Africa. Among the five species were three teleosts (Category I and IIa) and two elasmobranchs (Category I). A fish was considered to have remained resident if recaptured within 0-5 km after 365 days at liberty. A fish was considered to have undertaken a wide-ranging movement if recaptured more than 50 km away from the release site in 365 days or less. A total of 1848 individuals from the five study species were recaptured during the study, of which 73% of the observations were classified as being resident. Binomial logistic regression confirmed that species, life-stage (juvenile/adult) and ecoregion were significant (p < 0.001) predictors of the probability of wide-ranging behaviour. A Gaussian model confirmed that species and ecoregion were also significant (p < 0.001) predictors of direction and distance of wide-ranging movement. However, the direction and distance of wide-ranging movements in juveniles did not differ significantly (p > 0.05) to that of adults. The median growth rate was mostly greater in wide- ranging individuals; however, this was only statistically significant (p < 0.05) in two cases. These findings provide unequivocal evidence of life-cycle diversity in five fish species, with vastly different life-histories. This ecological phenomenon may provide species resilience at the population level and needs to be considered in fisheries management initiatives. The movement of fishes is a fundamental aspect to consider when designing fishery management regimes. Unfortunately, traditional management strategies have often disregarded movement behaviour to the detriment of fish populations (Chapter 6). As a case study, the management of Lichia amia (Category I: wide-ranging) was evaluated in the context of its movement behaviour. Long-term catch-per-unit-effort (CPUE) datasets were examined for three South African recreational fishery sectors. The CPUE was standardised using generalized linear models (delta-Gamma/hurdle approach) to reduce the effect of factors other than abundance. Factors that were available for this purpose were year, month and locality/zone. Year was included in every model as the primary objective was to detect trends in abundance over time. Although standardised CPUE for all sectors showed an overall long-term decline, there was considerable variability in trends between the different recreational sectors and between datasets. Contrasting trends between competitive shore angling and general shore angling datasets were ascribed to hyperstability in competitive CPUE data. Hyperstability in this case was mostly influenced by rapidly improving technology, techniques and communication networks amongst competitive anglers. Month and locality were significant factors explaining the probability of catching L. amia. This suggests that the predictable aggregatory behaviour of this species could further compound the observed CPUE hyperstability. Although the CPUE responded positively for six years after implementation of the first minimum size and bag limits, and for one year after the decommercialisation of the species, these regulations and their amendments failed to arrest a long-term decline in the CPUE despite the ample evidence for hyperstability. It is clear from this case study that the predictable nature of wide-ranging behaviour in L. amia has made the population vulnerable to exploitation. This has led to the demise in the population, which could have been worse if not for the occurrence of intra-population variability in its movement behaviour, which may provide some measure of resilience.
- Full Text:
- Date Issued: 2018
Population dynamics of selected ichthyofaunal components in the temperate, temporarily open/closed Kasouga Estuary, South Africa
- Authors: Tweddle, Gavin Paul
- Date: 2005
- Subjects: Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5742 , http://hdl.handle.net/10962/d1005428 , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Description: The spatial and temporal pattern of ichthyofaunal community composition in relation to selected physico-chemical (temperature and salinity) and biological variables (chlorophyll-a and zooplankton) was investigated at ten stations in the temperate temporarily open/closed Kasouga estuary. In addition, the food web structure in the estuary was investigated using stable carbon isotope analysis. Results of the 5 metre seine net survey indicated that ichthyofaunal composition and biomass in the Kasouga estuary was largely determined by seasonality and mouth condition. Maximum abundance and biomass of ichthyofauna was recorded during summer or during those periods when overtopping occurred. Overtopping coincided with the recruitment of marine estuarine dependant species, which dominated the catches both numerically and in biomass. The recruitment of these species resulted in an increase in diversity of the ichthyofaunal community. There were no significant spatial patterns in the distribution of smaller ichthyofauna (<50mm SL) identified in Bray-Curtis similarity matrices using cluster analysis (Primer 5 v5.2.4). Spearman’s correlation analysis revealed that there were no significant correlations between abundance and biomass of ichthyofauna and selected physico-chemical and biological variables other than salinity (P>0.05 in all other cases). There were two distinct spatial patterns in the distribution of the larger ichthyofauna (>50mm SL). These corresponded to a grouping associated with the mouth region and a grouping associated with the remaining regions of the estuary. Stable isotope analysis indicated that the primary source of carbon utilised by the ichthyofauna of the Kasouga estuary was derived from the channel, most likely microphytobenthic algae. The contributions of the riparian and salt marsh vegetation to the total carbon flow appear to be minimal.
- Full Text:
- Date Issued: 2005
- Authors: Tweddle, Gavin Paul
- Date: 2005
- Subjects: Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5742 , http://hdl.handle.net/10962/d1005428 , Estuaries -- South Africa -- Eastern Cape , Estuarine fishes -- South Africa -- Eastern Cape , Estuarine ecology -- South Africa -- Eastern Cape
- Description: The spatial and temporal pattern of ichthyofaunal community composition in relation to selected physico-chemical (temperature and salinity) and biological variables (chlorophyll-a and zooplankton) was investigated at ten stations in the temperate temporarily open/closed Kasouga estuary. In addition, the food web structure in the estuary was investigated using stable carbon isotope analysis. Results of the 5 metre seine net survey indicated that ichthyofaunal composition and biomass in the Kasouga estuary was largely determined by seasonality and mouth condition. Maximum abundance and biomass of ichthyofauna was recorded during summer or during those periods when overtopping occurred. Overtopping coincided with the recruitment of marine estuarine dependant species, which dominated the catches both numerically and in biomass. The recruitment of these species resulted in an increase in diversity of the ichthyofaunal community. There were no significant spatial patterns in the distribution of smaller ichthyofauna (<50mm SL) identified in Bray-Curtis similarity matrices using cluster analysis (Primer 5 v5.2.4). Spearman’s correlation analysis revealed that there were no significant correlations between abundance and biomass of ichthyofauna and selected physico-chemical and biological variables other than salinity (P>0.05 in all other cases). There were two distinct spatial patterns in the distribution of the larger ichthyofauna (>50mm SL). These corresponded to a grouping associated with the mouth region and a grouping associated with the remaining regions of the estuary. Stable isotope analysis indicated that the primary source of carbon utilised by the ichthyofauna of the Kasouga estuary was derived from the channel, most likely microphytobenthic algae. The contributions of the riparian and salt marsh vegetation to the total carbon flow appear to be minimal.
- Full Text:
- Date Issued: 2005
Salinity induced physiological responses in juvenile dusky kob, Argyrosomus japonicus (Sciaenidae)
- Authors: Bernatzeder, Andrea Katinka
- Date: 2009
- Subjects: Osmoregulation , Argyrosomus -- Effects of salt on -- South Africa , Sciaenidae -- Effects of salt on -- South Africa , Argyrosomus -- Physiology , Sciaenidae -- Physiology , Fishes -- Physiology , Biological control systems , Marine ecology -- South Africa , Fishery management -- South Africa , Mariculture -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5318 , http://hdl.handle.net/10962/d1005163 , Osmoregulation , Argyrosomus -- Effects of salt on -- South Africa , Sciaenidae -- Effects of salt on -- South Africa , Argyrosomus -- Physiology , Sciaenidae -- Physiology , Fishes -- Physiology , Biological control systems , Marine ecology -- South Africa , Fishery management -- South Africa , Mariculture -- South Africa
- Description: Fisheries management regulations for dusky kob Argyrosomus japonicus, an important commercial and recreational fisheries species, have failed and the stock is considered collapsed. It is important to take an ecosystems approach to management which includes understanding the effect of environmental factors on recruitment, abundance and distribution. The distribution of early juveniles (20-150 mm TL) in the wild appears to be restricted to the upper reaches of estuaries at salinities below 5 psu. Food availability could not explain the distribution of early juveniles. The aim of this study was to investigate the role of salinity on the distribution of early juvenile dusky kob (<150 mm TL) by examining physiological responses of juveniles exposed to a range of salinities under laboratory conditions. The hypothesis was that the physiological functioning of early juveniles would be optimised at the reduced salinities which they naturally occur at. The objectives of this study were to investigate the effect of salinity on: i) plasma osmolality; ii) growth, food conversion ratio and condition factor; and iii) gill histology with emphasis on chloride cell size and number. A preliminary study was undertaken to determine whether the use of 2-phenoxyethanol had an effect on plasma osmolality. Juveniles pithed prior to blood sampling were used as the control. Plasma osmolality was not affected by exposure or duration of exposure (2, 4, 6, 8, 10 min) to 2-phenoxyethanol. The ability of teleosts to regulate plasma osmolality over a wide range of salinities indicates their degree of ‘physiological euryhalinity’. Plasma osmolality of juveniles exposed to 5, 12 and 35 psu was measured every two weeks over a total of six weeks. Although juveniles were able to regulate plasma osmolality over the duration of the experiment, plasma osmolality at 5 and 12 psu was significantly lower than in fish maintained at 35 psu. Growth is used as an indicator of the relative energy used for osmoregulation at different salinities, as the energy used for osmoregulation becomes unavailable for growth. A nineweek growth experiment was conducted on juveniles exposed to 5, 12 and 35 psu. Juveniles grew and survived at all three salinities. However, growth of juveniles at 5 psu was significantly lower than at 12 and 35 psu. Other than a significantly greater weight gain at 35 psu relative to 12 psu, there was no significant difference in specific growth and length gain between juveniles at 12 and 35 psu. Food conversion ratio and condition factor at 12 and 35 psu were not significantly different, but food conversion ratio and condition factor at 5 psu was significantly greater and lower than at 35 psu respectively. In fish, gills are considered the major organ involved in osmoregulation. Within the gills, chloride cells are the predominant site of ion exchange which is driven by the Na⁺, K⁺- ATPase enzyme. Gill samples of juveniles exposed to 5, 12 and 35 psu for six weeks were examined histologically using light microscopy. Chloride cells of juveniles maintained at 5 psu were significantly more abundant than in juveniles at 12 and 35 psu. Chloride cells of juveniles at 5 psu were significantly larger than in juveniles kept at 12 psu, but not significantly different to those of juveniles kept at 35 psu. The ability of the juvenile fish to regulate plasma osmolality indicates that they are 'physiologically euryhaline', but the reduced growth and proliferation of chloride cells at 5 psu suggests that energy expenditure for osmoregulation is increased at hypoosmotic salinities. Salinity induced physiological responses could therefore not explain the natural distribution of early juvenile dusky kob and it is proposed that other environmental factors (e.g. temperature) are also important. It is also hypothesised that the high conductivity of an estuary in South Africa, to which our understanding is limited, may negate the effect of reduced salinity. Although freshwater input into estuaries is an important factor, further investigations to explain the distribution and abundance of early juveniles is required to make management recommendations. Dusky kob is also becoming an increasingly popular aquaculture species in South Africa. In this regard, early juvenile dusky kob can be grown at salinities as low as 12 psu without negatively affecting growth and production.
- Full Text:
- Date Issued: 2009
- Authors: Bernatzeder, Andrea Katinka
- Date: 2009
- Subjects: Osmoregulation , Argyrosomus -- Effects of salt on -- South Africa , Sciaenidae -- Effects of salt on -- South Africa , Argyrosomus -- Physiology , Sciaenidae -- Physiology , Fishes -- Physiology , Biological control systems , Marine ecology -- South Africa , Fishery management -- South Africa , Mariculture -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5318 , http://hdl.handle.net/10962/d1005163 , Osmoregulation , Argyrosomus -- Effects of salt on -- South Africa , Sciaenidae -- Effects of salt on -- South Africa , Argyrosomus -- Physiology , Sciaenidae -- Physiology , Fishes -- Physiology , Biological control systems , Marine ecology -- South Africa , Fishery management -- South Africa , Mariculture -- South Africa
- Description: Fisheries management regulations for dusky kob Argyrosomus japonicus, an important commercial and recreational fisheries species, have failed and the stock is considered collapsed. It is important to take an ecosystems approach to management which includes understanding the effect of environmental factors on recruitment, abundance and distribution. The distribution of early juveniles (20-150 mm TL) in the wild appears to be restricted to the upper reaches of estuaries at salinities below 5 psu. Food availability could not explain the distribution of early juveniles. The aim of this study was to investigate the role of salinity on the distribution of early juvenile dusky kob (<150 mm TL) by examining physiological responses of juveniles exposed to a range of salinities under laboratory conditions. The hypothesis was that the physiological functioning of early juveniles would be optimised at the reduced salinities which they naturally occur at. The objectives of this study were to investigate the effect of salinity on: i) plasma osmolality; ii) growth, food conversion ratio and condition factor; and iii) gill histology with emphasis on chloride cell size and number. A preliminary study was undertaken to determine whether the use of 2-phenoxyethanol had an effect on plasma osmolality. Juveniles pithed prior to blood sampling were used as the control. Plasma osmolality was not affected by exposure or duration of exposure (2, 4, 6, 8, 10 min) to 2-phenoxyethanol. The ability of teleosts to regulate plasma osmolality over a wide range of salinities indicates their degree of ‘physiological euryhalinity’. Plasma osmolality of juveniles exposed to 5, 12 and 35 psu was measured every two weeks over a total of six weeks. Although juveniles were able to regulate plasma osmolality over the duration of the experiment, plasma osmolality at 5 and 12 psu was significantly lower than in fish maintained at 35 psu. Growth is used as an indicator of the relative energy used for osmoregulation at different salinities, as the energy used for osmoregulation becomes unavailable for growth. A nineweek growth experiment was conducted on juveniles exposed to 5, 12 and 35 psu. Juveniles grew and survived at all three salinities. However, growth of juveniles at 5 psu was significantly lower than at 12 and 35 psu. Other than a significantly greater weight gain at 35 psu relative to 12 psu, there was no significant difference in specific growth and length gain between juveniles at 12 and 35 psu. Food conversion ratio and condition factor at 12 and 35 psu were not significantly different, but food conversion ratio and condition factor at 5 psu was significantly greater and lower than at 35 psu respectively. In fish, gills are considered the major organ involved in osmoregulation. Within the gills, chloride cells are the predominant site of ion exchange which is driven by the Na⁺, K⁺- ATPase enzyme. Gill samples of juveniles exposed to 5, 12 and 35 psu for six weeks were examined histologically using light microscopy. Chloride cells of juveniles maintained at 5 psu were significantly more abundant than in juveniles at 12 and 35 psu. Chloride cells of juveniles at 5 psu were significantly larger than in juveniles kept at 12 psu, but not significantly different to those of juveniles kept at 35 psu. The ability of the juvenile fish to regulate plasma osmolality indicates that they are 'physiologically euryhaline', but the reduced growth and proliferation of chloride cells at 5 psu suggests that energy expenditure for osmoregulation is increased at hypoosmotic salinities. Salinity induced physiological responses could therefore not explain the natural distribution of early juvenile dusky kob and it is proposed that other environmental factors (e.g. temperature) are also important. It is also hypothesised that the high conductivity of an estuary in South Africa, to which our understanding is limited, may negate the effect of reduced salinity. Although freshwater input into estuaries is an important factor, further investigations to explain the distribution and abundance of early juveniles is required to make management recommendations. Dusky kob is also becoming an increasingly popular aquaculture species in South Africa. In this regard, early juvenile dusky kob can be grown at salinities as low as 12 psu without negatively affecting growth and production.
- Full Text:
- Date Issued: 2009
Movement behaviour and reproductive biology of adult spotted grunter (Pomadasys commersonnii) in the Breede Estuary
- Authors: Ziko, Bantony Alford
- Date: 2021-06
- Subjects: Fishery management , Freshwater fishes , Fishes--Nutrition
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20970 , vital:46870
- Description: Movements of the adult spotted grunter (Pomadasys commersonnii), an overexploited estuary-dependant fishery species, were investigated in relation to its reproduction behaviour and selected environmental influences. The South African P. commersonnii population is known to spawn at sea along the KwaZulu-Natal (KZN) coastline, whereas there no published records on spawning in the Eastern and Western Cape Provinces exist. However, due to the occurrence of ripe running fish that were reported in the Breede Estuary (Western Cape - WC), an investigation into its reproductive behaviour was necessary, as was gaining a greater understanding of its movements between the estuary, the sea, and other connected habitats. Seven adult P. commersonnii (610 – 690 mm fork length, FL) were captured and implanted with long-life acoustic transmitters and their movements were logged on a linear array of 16 acoustic receivers in the Breede Estuary (WC) and six acoustic receivers in the adjacent marine environment. Movements of the tagged fish to other marine and estuary habitats were also determined using data collected by the Acoustic Tracking Array Platform (ATAP) which is an extended network of acoustic receivers along the South African coastline with receivers at sea and in selected estuaries. Furthermore, adult P. commersonnii tagged in the Goukou (n = 6) (WC) and Sundays (n = 8) (Eastern Cape - EC) estuaries, approximately 50 km and 470 km away, respectively, were also monitored to facilitate an improved understanding of inter-habitat connectivity. Fish tagged in Sundays and Goukou estuaries were monitored by the Acoustic Telemetry Array Platform (ATAP). Each individual fish tagged in the Breede Estuary was monitored between 356 and 1166 days and selected environmental parameters, including water temperature, river flow rate and rainfall, were measured during the study period (November 2016 – March 2020) to assess their influence on the movements of the tagged fish. Furthermore, to determine time of spawning and duration, gonads of 112 adult fish (383 – 700 mm FL) were opportunistically collected from recreational anglers in the Breede Estuary to determine the gonadal maturation cycles by using a combination of Gonado-somatic index (GSI) and histology. The tagged adult P. commersonnii spent significantly more time in the estuary (83.5 percent) than the marine (16.5 percent) environment, with all of the tagged P. commersonnii making sea trips of varying frequency and duration. While in the estuary, fish showed a strong preference for the lower reaches of the estuary compared to the middle and upper reaches. Area use varied seasonally, with the mouth area being heavily utilized during winter, then followed by summer. Sea trips in all three tagging estuaries also fluctuated seasonally, with more frequent movements during summer which lasted for longer periods. This coincided with the peak of the spawning period inferred from the gonad developmental cycle of fish captured in the Breede Estuary. Results from a generalized linear mixed model showed that the presence of Breede tagged P. commersonnii in the sea, where the species is known to spawn, was significantly influenced by water temperatures in the estuary and river flow rate with fish more likely to occur at sea during warmer months (summer) and periods of high river flow (winter). Furthermore, circular analysis showed that season (month) had a significant influence on the departure from and arrival in the Breede Estuary, with most departures and arrivals occurring during January. Moreover, P. commersonnii tagged in the Sundays Estuary also showed similar results where both departures and arrivals were influenced by season, mostly taking place in December and January, respectively. The increased frequency of sea trips by adult P. commersonnii in summer suggests regional spawning occurring in the WC. Based on the similar movement behaviour displayed by tagged fish in the Sundays Estuary, it is possible that spawning also occurs in the EC. Most of the P. commersonnii tagged in all the three estuaries never left their tagging estuaries (57 percent Breede, 66 percent Goukou, 38 percent Sundays), only making short sea trips, while others displayed use of multiple habitats. On average, the tagged P. commersonnii that left their tagging estuaries travelled a maximum distance of 377 km (Breede), 63 km (Goukou) and 300 km (Sundays). Tagged fish were more likely to visit nearby estuaries and offshore marine habitats (< 130 km) compared to distant ones (> 130 km). These results suggest that there are high levels of localised connectivity between P. commersonnii populations in different habitats although connectivity between distant habitats appears to be rare. Connectivity will likely occur on habitats located close to the boundaries of the WC, EC and KZN. The findings from this long-term monitoring study have shown that adult P. commersonnii rely heavily on the estuarine environment, undertaking short sea trips, thus demonstrating the importance of estuaries to the adult population. Due to various threats faced by estuaries such as habitat degradation and overexploitation, management of these systems is paramount to conserve such fishery resources. Due to the resident behaviour of the P. commersonnii within estuaries, Marine Protected Areas (MPAs) and area closures, in conjunction with Estuarine Protected Areas (EPAs) will be significant in the recovery and management of P. commersonnii populations. Since P. commersonnii appears to reach peak spawning activity during summer when fishing pressure is usually highest, improved enforcement during this period is necessary to conserve the spawning stock. As connectivity is an important aspect in the life of the P. commersonnii, ensuring such connectivity is maintained by protecting all these habitats is important. , Thesis (MSc) (Zoology) -- University of Fort Hare, 2021
- Full Text:
- Date Issued: 2021-06
- Authors: Ziko, Bantony Alford
- Date: 2021-06
- Subjects: Fishery management , Freshwater fishes , Fishes--Nutrition
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/20970 , vital:46870
- Description: Movements of the adult spotted grunter (Pomadasys commersonnii), an overexploited estuary-dependant fishery species, were investigated in relation to its reproduction behaviour and selected environmental influences. The South African P. commersonnii population is known to spawn at sea along the KwaZulu-Natal (KZN) coastline, whereas there no published records on spawning in the Eastern and Western Cape Provinces exist. However, due to the occurrence of ripe running fish that were reported in the Breede Estuary (Western Cape - WC), an investigation into its reproductive behaviour was necessary, as was gaining a greater understanding of its movements between the estuary, the sea, and other connected habitats. Seven adult P. commersonnii (610 – 690 mm fork length, FL) were captured and implanted with long-life acoustic transmitters and their movements were logged on a linear array of 16 acoustic receivers in the Breede Estuary (WC) and six acoustic receivers in the adjacent marine environment. Movements of the tagged fish to other marine and estuary habitats were also determined using data collected by the Acoustic Tracking Array Platform (ATAP) which is an extended network of acoustic receivers along the South African coastline with receivers at sea and in selected estuaries. Furthermore, adult P. commersonnii tagged in the Goukou (n = 6) (WC) and Sundays (n = 8) (Eastern Cape - EC) estuaries, approximately 50 km and 470 km away, respectively, were also monitored to facilitate an improved understanding of inter-habitat connectivity. Fish tagged in Sundays and Goukou estuaries were monitored by the Acoustic Telemetry Array Platform (ATAP). Each individual fish tagged in the Breede Estuary was monitored between 356 and 1166 days and selected environmental parameters, including water temperature, river flow rate and rainfall, were measured during the study period (November 2016 – March 2020) to assess their influence on the movements of the tagged fish. Furthermore, to determine time of spawning and duration, gonads of 112 adult fish (383 – 700 mm FL) were opportunistically collected from recreational anglers in the Breede Estuary to determine the gonadal maturation cycles by using a combination of Gonado-somatic index (GSI) and histology. The tagged adult P. commersonnii spent significantly more time in the estuary (83.5 percent) than the marine (16.5 percent) environment, with all of the tagged P. commersonnii making sea trips of varying frequency and duration. While in the estuary, fish showed a strong preference for the lower reaches of the estuary compared to the middle and upper reaches. Area use varied seasonally, with the mouth area being heavily utilized during winter, then followed by summer. Sea trips in all three tagging estuaries also fluctuated seasonally, with more frequent movements during summer which lasted for longer periods. This coincided with the peak of the spawning period inferred from the gonad developmental cycle of fish captured in the Breede Estuary. Results from a generalized linear mixed model showed that the presence of Breede tagged P. commersonnii in the sea, where the species is known to spawn, was significantly influenced by water temperatures in the estuary and river flow rate with fish more likely to occur at sea during warmer months (summer) and periods of high river flow (winter). Furthermore, circular analysis showed that season (month) had a significant influence on the departure from and arrival in the Breede Estuary, with most departures and arrivals occurring during January. Moreover, P. commersonnii tagged in the Sundays Estuary also showed similar results where both departures and arrivals were influenced by season, mostly taking place in December and January, respectively. The increased frequency of sea trips by adult P. commersonnii in summer suggests regional spawning occurring in the WC. Based on the similar movement behaviour displayed by tagged fish in the Sundays Estuary, it is possible that spawning also occurs in the EC. Most of the P. commersonnii tagged in all the three estuaries never left their tagging estuaries (57 percent Breede, 66 percent Goukou, 38 percent Sundays), only making short sea trips, while others displayed use of multiple habitats. On average, the tagged P. commersonnii that left their tagging estuaries travelled a maximum distance of 377 km (Breede), 63 km (Goukou) and 300 km (Sundays). Tagged fish were more likely to visit nearby estuaries and offshore marine habitats (< 130 km) compared to distant ones (> 130 km). These results suggest that there are high levels of localised connectivity between P. commersonnii populations in different habitats although connectivity between distant habitats appears to be rare. Connectivity will likely occur on habitats located close to the boundaries of the WC, EC and KZN. The findings from this long-term monitoring study have shown that adult P. commersonnii rely heavily on the estuarine environment, undertaking short sea trips, thus demonstrating the importance of estuaries to the adult population. Due to various threats faced by estuaries such as habitat degradation and overexploitation, management of these systems is paramount to conserve such fishery resources. Due to the resident behaviour of the P. commersonnii within estuaries, Marine Protected Areas (MPAs) and area closures, in conjunction with Estuarine Protected Areas (EPAs) will be significant in the recovery and management of P. commersonnii populations. Since P. commersonnii appears to reach peak spawning activity during summer when fishing pressure is usually highest, improved enforcement during this period is necessary to conserve the spawning stock. As connectivity is an important aspect in the life of the P. commersonnii, ensuring such connectivity is maintained by protecting all these habitats is important. , Thesis (MSc) (Zoology) -- University of Fort Hare, 2021
- Full Text:
- Date Issued: 2021-06
Rhodes University Research Report 2013
- Rhodes University, Roberts, Jaine, Mantolo, Thumeka, Jacob, Patricia, Macgregor, Jill, Dore, Sally
- Authors: Rhodes University , Roberts, Jaine , Mantolo, Thumeka , Jacob, Patricia , Macgregor, Jill , Dore, Sally
- Date: 2013
- Language: English
- Type: Text
- Identifier: http://hdl.handle.net/10962/59330 , vital:27549
- Description: From Foreword by Dr Saleem Badat: Rhodes University has positioned itself as a research university that, alongside excellence in undergraduate teaching, also takes scholarship seriously. This has strongly shaped the intellectual identity of the university and, today, research income and expenditure are significant components of the university’s finances. Rhodes University values the scholar-teacher model of combining research with teaching and learning, and other scholarly activities. This has a strong influence on the quality of intellectual endeavour at the University, and is critical in advancing the University’s pursuit of a strong postgraduate trajectory. This is an opportunity to briefly reflect on research at Rhodes over the eight years of my Vice-Chancellorship. It is gratifying to see that scholarship and publishing has continued to blossom at Rhodes, and has also occurred over a wider academic base, and that there has also been increased enrolments of postgraduates, as part of overall University strategy. Postgraduate enrolments increased from 24% (1 397) in 2006 to 30% (2 302) in 2013, with considerable increases in the numbers of Masters and Doctoral students. Between 2006 and 2013, Honours and Postgraduate Diploma graduations increased from 453 to 719, Masters graduations increased by 73% (from 171 to 296) and Doctoral graduations by 70% (from 46 to 78). Concomitantly, there was an increase in the numbers of black and women PhD graduates. The number of Postdoctoral Fellows at Rhodes rose from 19 in 2007 to 68 in 2013, an increase of 258%. , A publication of the Rhodes University Research Office, compiled and edited by Jaine Roberts, Thumeka Mantolo, Patricia Jacob and Jill Macgregor. Design and Layout: Sally Dore
- Full Text:
- Date Issued: 2013
- Authors: Rhodes University , Roberts, Jaine , Mantolo, Thumeka , Jacob, Patricia , Macgregor, Jill , Dore, Sally
- Date: 2013
- Language: English
- Type: Text
- Identifier: http://hdl.handle.net/10962/59330 , vital:27549
- Description: From Foreword by Dr Saleem Badat: Rhodes University has positioned itself as a research university that, alongside excellence in undergraduate teaching, also takes scholarship seriously. This has strongly shaped the intellectual identity of the university and, today, research income and expenditure are significant components of the university’s finances. Rhodes University values the scholar-teacher model of combining research with teaching and learning, and other scholarly activities. This has a strong influence on the quality of intellectual endeavour at the University, and is critical in advancing the University’s pursuit of a strong postgraduate trajectory. This is an opportunity to briefly reflect on research at Rhodes over the eight years of my Vice-Chancellorship. It is gratifying to see that scholarship and publishing has continued to blossom at Rhodes, and has also occurred over a wider academic base, and that there has also been increased enrolments of postgraduates, as part of overall University strategy. Postgraduate enrolments increased from 24% (1 397) in 2006 to 30% (2 302) in 2013, with considerable increases in the numbers of Masters and Doctoral students. Between 2006 and 2013, Honours and Postgraduate Diploma graduations increased from 453 to 719, Masters graduations increased by 73% (from 171 to 296) and Doctoral graduations by 70% (from 46 to 78). Concomitantly, there was an increase in the numbers of black and women PhD graduates. The number of Postdoctoral Fellows at Rhodes rose from 19 in 2007 to 68 in 2013, an increase of 258%. , A publication of the Rhodes University Research Office, compiled and edited by Jaine Roberts, Thumeka Mantolo, Patricia Jacob and Jill Macgregor. Design and Layout: Sally Dore
- Full Text:
- Date Issued: 2013