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
Movement patterns of Cape stumpnose, Rhabdosargus holubi (Sparidae), in the Kowie Estuary, South Africa
- Authors: Grant, Gareth Neil
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/982 , vital:20010
- Description: Rhabdosargus holubi is an ubiquitous estuary-dependent fishery species endemic to southern Africa. Although aspects of its recruitment dynamics from sea to estuary have received considerable research attention, little is known about its movement behaviour within estuarine systems. Fishery surveys have also revealed that R. holubi is a dominant species in catches within several temperate estuaries in South Africa. Therefore, investigating movement behaviour is fundamental to understanding the ecology of this species and providing a means for implementing effective fisheries management strategies. This study made use of passive acoustic telemetry to quantify the movement patterns of juvenile R. holubi in the Kowie Estuary, in the Eastern Cape Province of South Africa. Previous studies have revealed that surgically implanted transmitters may have adverse effects on the physiology and behaviour of tagged fish. Therefore, due to the small size of juvenile R. holubi, an a priori transmitter-effect experiment was undertaken. This experiment revealed that juvenile R. holubi (146-217 mm fork length) were not adversely affected by the surgical implantation of acoustic transmitters (7 mm Ø, 1.6 g out of water) and hence acoustic telemetry was well suited to monitoring the movements of this species. A 4-month telemetry study evaluated the movement patterns of 21 juveniles (140-190 mm fork length) tagged in three equal batches along the length of the estuary. Specific aspects of their movement included space use patterns, habitat connectivity, and the influences of geophysical cycles and environmental variables. Tagged fish exhibited high residency, which varied between each release site area. The mean length of estuary used was greater for the upper batch (15.65 ± 6.49 km) than the middle and lower batches (7.36 ± 3.68 and 2.67 ± 2 km, respectively). In terms of habitat connectivity, once the tagged fish left the estuary, they generally did not return. Tagged R. holubi spent the majority (83%) of their monitoring periods within the estuarine environment, with the sea (16%) and riverine (1%) environments being utilised to a lesser extent. Diel and tidal cycles influenced the movement patterns of juvenile R. holubi. However, the high levels of residency meant that fine-scale movements were difficult to detect due to the acoustic receiver deployment configuration (i.e. receivers moored one kilometer apart). The influence of environmental variables on the movement of individuals, modelled with general linear mixed models (GLMMs), revealed that the effects of river inflow and water temperature were greatest. Increased river inflow caused individuals to use larger portions of the estuary. Increased water temperature, particularly river temperature, caused individuals to shift their distributions downstream (towards the mouth of the estuary). This study highlighted the importance of estuarine nursery habitats to R. holubi, suggesting that a loss or reduction of healthy estuarine habitats may lead to significant declines in the abundance of this species. Furthermore, extreme resident behaviour suggests that no-take area closures (estuarine protected areas) would be an effective management strategy for this important fishery species.
- Full Text:
- Date Issued: 2016
- Authors: Grant, Gareth Neil
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/982 , vital:20010
- Description: Rhabdosargus holubi is an ubiquitous estuary-dependent fishery species endemic to southern Africa. Although aspects of its recruitment dynamics from sea to estuary have received considerable research attention, little is known about its movement behaviour within estuarine systems. Fishery surveys have also revealed that R. holubi is a dominant species in catches within several temperate estuaries in South Africa. Therefore, investigating movement behaviour is fundamental to understanding the ecology of this species and providing a means for implementing effective fisheries management strategies. This study made use of passive acoustic telemetry to quantify the movement patterns of juvenile R. holubi in the Kowie Estuary, in the Eastern Cape Province of South Africa. Previous studies have revealed that surgically implanted transmitters may have adverse effects on the physiology and behaviour of tagged fish. Therefore, due to the small size of juvenile R. holubi, an a priori transmitter-effect experiment was undertaken. This experiment revealed that juvenile R. holubi (146-217 mm fork length) were not adversely affected by the surgical implantation of acoustic transmitters (7 mm Ø, 1.6 g out of water) and hence acoustic telemetry was well suited to monitoring the movements of this species. A 4-month telemetry study evaluated the movement patterns of 21 juveniles (140-190 mm fork length) tagged in three equal batches along the length of the estuary. Specific aspects of their movement included space use patterns, habitat connectivity, and the influences of geophysical cycles and environmental variables. Tagged fish exhibited high residency, which varied between each release site area. The mean length of estuary used was greater for the upper batch (15.65 ± 6.49 km) than the middle and lower batches (7.36 ± 3.68 and 2.67 ± 2 km, respectively). In terms of habitat connectivity, once the tagged fish left the estuary, they generally did not return. Tagged R. holubi spent the majority (83%) of their monitoring periods within the estuarine environment, with the sea (16%) and riverine (1%) environments being utilised to a lesser extent. Diel and tidal cycles influenced the movement patterns of juvenile R. holubi. However, the high levels of residency meant that fine-scale movements were difficult to detect due to the acoustic receiver deployment configuration (i.e. receivers moored one kilometer apart). The influence of environmental variables on the movement of individuals, modelled with general linear mixed models (GLMMs), revealed that the effects of river inflow and water temperature were greatest. Increased river inflow caused individuals to use larger portions of the estuary. Increased water temperature, particularly river temperature, caused individuals to shift their distributions downstream (towards the mouth of the estuary). This study highlighted the importance of estuarine nursery habitats to R. holubi, suggesting that a loss or reduction of healthy estuarine habitats may lead to significant declines in the abundance of this species. Furthermore, extreme resident behaviour suggests that no-take area closures (estuarine protected areas) would be an effective management strategy for this important fishery species.
- Full Text:
- Date Issued: 2016
Movement patterns of spotted grunter, Pomadasys commersonnii (Haemulidae), in a highly turbid South African estuary
- Authors: Childs, Amber-Robyn
- Date: 2006
- Subjects: Grunts (Fishes) -- South Africa -- Great Fish River , Pomadasys -- South Africa -- Great Fish River , Freshwater fishes -- South Africa -- Great Fish River , Fishes -- Behavior -- South Africa -- Great Fish River , Estuarine fishes -- South Africa -- Great Fish River , Estaurine ecology -- South Africa -- Great Fish River , Marine ecology -- South Africa -- Great Fish River
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5304 , http://hdl.handle.net/10962/d1005149 , Grunts (Fishes) -- South Africa -- Great Fish River , Pomadasys -- South Africa -- Great Fish River , Freshwater fishes -- South Africa -- Great Fish River , Fishes -- Behavior -- South Africa -- Great Fish River , Estuarine fishes -- South Africa -- Great Fish River , Estaurine ecology -- South Africa -- Great Fish River , Marine ecology -- South Africa -- Great Fish River
- Description: The principal objective of this thesis was to gain an understanding of the movement patterns of spotted grunter Pomadasys commersonnii, an estuarine-dependent fishery species, in the turbid, freshwater dominated Great Fish Estuary. Both manual and automated telemetry methods were used to monitor the movements of spotted grunter during two separate studies conducted in summer and spring 2003 and 2004. Acoustic transmitters were surgically implanted into twenty spotted grunter with lengths between 263 and 387 mm TL in the first study and twenty spotted grunter ranging between 362 and 698 mm TL in the second study. The specific objectives were to gain an understanding of (i) the time spent in the estuarine environment (ii) the space use and home range size, and (iii) the abiotic factors governing the movement patterns of spotted grunter in the estuary. The nursery function of estuarine environments was highlighted in this study as adolescent spotted grunter spent a significantly larger proportion of their time in the estuary than adult fish (p < 0.0001; R² = 0.62). The increased frequency of sea trips, with the onset of sexual maturity, provided testimony of the end of the estuarinedependent phase of their life-cycle. Although considered to be predominantly marine, the adult spotted grunter in the Great Fish Estuary utilised the estuary for considerable periods. Adults are thought to frequent estuaries to forage, seek shelter and to possibly rid themselves of parasites. During this study, the number of sea trips made by tagged fish ranged from 0 to 53, and the duration ranged from 6 hours to 28 days. The tidal phase and time of day had a significant effect (p < 0.05) on the sea trips undertaken by fish. Most tagged spotted grunter left the estuary during the night (84%) on the outgoing tide, and most returned in the evening (77%) during the incoming tide. Sea temperature (p < 0.0001; R² = 0.34), barometric pressure (p = 0.004; R² = 0.19) and wind (p = 0.01) had a significant effect on the number of spotted grunter recorded in the estuary. Spotted grunter were more prone to return to the estuary after high barometric pressure, when low sea temperatures (upwelling events) prevailed. There was a significant positive relationship between home range size and fish length (p = 0.004; R² = 0.20). Small spotted grunter (< 450 mm TL) appeared to be highly resident, with a small home range (mean size = 129 167 m²), that was generally confined to a single core area. Larger individuals (> 450 mm TL) occupied larger home ranges (mean size = 218 435 m²) with numerous core areas. The home ranges of small and large spotted grunter overlapped considerably yielding evidence of two high use areas, situated 1.2 km and 7 km from the mouth of the Great Fish Estuary. Tagged spotted grunter were located in a wide range of salinity, turbidity and temperature, but were found to avoid temperatures below 16 ºC. The daily change in environmental variables (salinity, temperature and turbidity) had a significant effect on the change in fish position in the estuary (p < 0.0001; R² = 0.38). The distribution of tagged spotted grunter, particularly the larger individuals, in the Great Fish Estuary was influenced by the tidal phase (p < 0.05); they moved upriver on the incoming tide and downriver on the outgoing tide. This study provides an understanding of the movement patterns of spotted grunter in the estuary and between the estuarine and marine environments. Consequently, it provides information that will assist in the design of a management plan to promote sustainability of this important fishery species. The techniques used and developed in this study also have direct application for further studies on other important estuarinedependent fishery species.
- Full Text:
- Date Issued: 2006
- Authors: Childs, Amber-Robyn
- Date: 2006
- Subjects: Grunts (Fishes) -- South Africa -- Great Fish River , Pomadasys -- South Africa -- Great Fish River , Freshwater fishes -- South Africa -- Great Fish River , Fishes -- Behavior -- South Africa -- Great Fish River , Estuarine fishes -- South Africa -- Great Fish River , Estaurine ecology -- South Africa -- Great Fish River , Marine ecology -- South Africa -- Great Fish River
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5304 , http://hdl.handle.net/10962/d1005149 , Grunts (Fishes) -- South Africa -- Great Fish River , Pomadasys -- South Africa -- Great Fish River , Freshwater fishes -- South Africa -- Great Fish River , Fishes -- Behavior -- South Africa -- Great Fish River , Estuarine fishes -- South Africa -- Great Fish River , Estaurine ecology -- South Africa -- Great Fish River , Marine ecology -- South Africa -- Great Fish River
- Description: The principal objective of this thesis was to gain an understanding of the movement patterns of spotted grunter Pomadasys commersonnii, an estuarine-dependent fishery species, in the turbid, freshwater dominated Great Fish Estuary. Both manual and automated telemetry methods were used to monitor the movements of spotted grunter during two separate studies conducted in summer and spring 2003 and 2004. Acoustic transmitters were surgically implanted into twenty spotted grunter with lengths between 263 and 387 mm TL in the first study and twenty spotted grunter ranging between 362 and 698 mm TL in the second study. The specific objectives were to gain an understanding of (i) the time spent in the estuarine environment (ii) the space use and home range size, and (iii) the abiotic factors governing the movement patterns of spotted grunter in the estuary. The nursery function of estuarine environments was highlighted in this study as adolescent spotted grunter spent a significantly larger proportion of their time in the estuary than adult fish (p < 0.0001; R² = 0.62). The increased frequency of sea trips, with the onset of sexual maturity, provided testimony of the end of the estuarinedependent phase of their life-cycle. Although considered to be predominantly marine, the adult spotted grunter in the Great Fish Estuary utilised the estuary for considerable periods. Adults are thought to frequent estuaries to forage, seek shelter and to possibly rid themselves of parasites. During this study, the number of sea trips made by tagged fish ranged from 0 to 53, and the duration ranged from 6 hours to 28 days. The tidal phase and time of day had a significant effect (p < 0.05) on the sea trips undertaken by fish. Most tagged spotted grunter left the estuary during the night (84%) on the outgoing tide, and most returned in the evening (77%) during the incoming tide. Sea temperature (p < 0.0001; R² = 0.34), barometric pressure (p = 0.004; R² = 0.19) and wind (p = 0.01) had a significant effect on the number of spotted grunter recorded in the estuary. Spotted grunter were more prone to return to the estuary after high barometric pressure, when low sea temperatures (upwelling events) prevailed. There was a significant positive relationship between home range size and fish length (p = 0.004; R² = 0.20). Small spotted grunter (< 450 mm TL) appeared to be highly resident, with a small home range (mean size = 129 167 m²), that was generally confined to a single core area. Larger individuals (> 450 mm TL) occupied larger home ranges (mean size = 218 435 m²) with numerous core areas. The home ranges of small and large spotted grunter overlapped considerably yielding evidence of two high use areas, situated 1.2 km and 7 km from the mouth of the Great Fish Estuary. Tagged spotted grunter were located in a wide range of salinity, turbidity and temperature, but were found to avoid temperatures below 16 ºC. The daily change in environmental variables (salinity, temperature and turbidity) had a significant effect on the change in fish position in the estuary (p < 0.0001; R² = 0.38). The distribution of tagged spotted grunter, particularly the larger individuals, in the Great Fish Estuary was influenced by the tidal phase (p < 0.05); they moved upriver on the incoming tide and downriver on the outgoing tide. This study provides an understanding of the movement patterns of spotted grunter in the estuary and between the estuarine and marine environments. Consequently, it provides information that will assist in the design of a management plan to promote sustainability of this important fishery species. The techniques used and developed in this study also have direct application for further studies on other important estuarinedependent fishery species.
- Full Text:
- Date Issued: 2006
Movement patterns of the iconic giant kingfish Caranx ignobilis from Southern Africa
- Authors: Dixon, Russell Bruce
- Date: 2022-10-14
- Subjects: Caranx Africa, Southern , Caranx Migration , Underwater acoustic telemetry , Carangidae Africa, Southern , Fish tagging
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362797 , vital:65363
- Description: Giant kingfish Caranx ignobilis, the largest species in the family Carangidae, are global icons as apex marine predators. They are widespread in tropical to subtropical regions globally, where they are of high importance to ecosystems and fisheries. During summer, adults aggregate for spawning, making them vulnerable to overfishing. The world’s largest recorded C. ignobilis aggregation is in southern Mozambique. Some of these aggregating individuals (an unknown proportion) have been recorded passing into South African waters. Furthermore, a unique aggregation of adult C. ignobilis in South Africa’s Mtentu Estuary has attracted global attention but remains unexplained, hence warranting investigation. Research on C. ignobilis globally has shown relatively small home ranges. Research in southern Africa has been limited and inconclusive. Thus, the broad aim of this study is to describe the movement patterns of C. ignobilis from southern Africa. Long-term (36 years) mark-recapture data from the Oceanographic Research Institute’s Co-operative Fish Tagging Project, comprising 3 729 tagged C. ignobilis and 144 recaptures, were analysed. While 74% of recaptures were recorded < 1 km from the tagging location, long-distance movements of up to 419 km were also recorded (mean = 15 km). Although adults moved significantly (p < 0.01) greater distances than juveniles, they also displayed high levels of site fidelity. Seasonal trends included evidence of a summer migration; however, there was still considerable uncertainty regarding exact movements. Therefore, 43 C. ignobilis were acoustically tagged and subsequently monitored along the east coast for over five years with the Acoustic Tracking Array Platform’s passive receiver array. All acoustically tagged adult C. ignobilis migrated to southern Mozambique each year (with minor exceptions), from distances of up to 632 km. When not migrating, South African-based fish showed consistent inter-annual fidelity to individual home ranges. Although coastal home range length (excluding migrations) varied considerably between individuals, even the mean length (92 km) was greater than any previously recorded C. ignobilis home range, globally. In contrast to the southern Mozambique aggregation, the Mtentu Estuary aggregation seems to comprise of individuals showing fidelity to that region. The passive tracking of eight acoustically tagged individuals in the Mtentu Estuary revealed clear trends. Statistical modelling showed that estuarine presence was strongly associated with periods of cold coastal upwelling. Diel movement patterns showed that the utilisation of warm surface waters ~ 4 km upstream during the day was followed by nightly departures to the mouth or sea. Thus, it is likely that this majestic aggregation is for thermal refuge; specifically, for daily re-warming after feeding in cold waters at night. Findings from this study are of global ecological interest and have direct applications for local fisheries management and the development of sustainable eco-tourism. Protecting these vulnerable aggregations is of the utmost importance for the future of this species in southern Africa. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Dixon, Russell Bruce
- Date: 2022-10-14
- Subjects: Caranx Africa, Southern , Caranx Migration , Underwater acoustic telemetry , Carangidae Africa, Southern , Fish tagging
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362797 , vital:65363
- Description: Giant kingfish Caranx ignobilis, the largest species in the family Carangidae, are global icons as apex marine predators. They are widespread in tropical to subtropical regions globally, where they are of high importance to ecosystems and fisheries. During summer, adults aggregate for spawning, making them vulnerable to overfishing. The world’s largest recorded C. ignobilis aggregation is in southern Mozambique. Some of these aggregating individuals (an unknown proportion) have been recorded passing into South African waters. Furthermore, a unique aggregation of adult C. ignobilis in South Africa’s Mtentu Estuary has attracted global attention but remains unexplained, hence warranting investigation. Research on C. ignobilis globally has shown relatively small home ranges. Research in southern Africa has been limited and inconclusive. Thus, the broad aim of this study is to describe the movement patterns of C. ignobilis from southern Africa. Long-term (36 years) mark-recapture data from the Oceanographic Research Institute’s Co-operative Fish Tagging Project, comprising 3 729 tagged C. ignobilis and 144 recaptures, were analysed. While 74% of recaptures were recorded < 1 km from the tagging location, long-distance movements of up to 419 km were also recorded (mean = 15 km). Although adults moved significantly (p < 0.01) greater distances than juveniles, they also displayed high levels of site fidelity. Seasonal trends included evidence of a summer migration; however, there was still considerable uncertainty regarding exact movements. Therefore, 43 C. ignobilis were acoustically tagged and subsequently monitored along the east coast for over five years with the Acoustic Tracking Array Platform’s passive receiver array. All acoustically tagged adult C. ignobilis migrated to southern Mozambique each year (with minor exceptions), from distances of up to 632 km. When not migrating, South African-based fish showed consistent inter-annual fidelity to individual home ranges. Although coastal home range length (excluding migrations) varied considerably between individuals, even the mean length (92 km) was greater than any previously recorded C. ignobilis home range, globally. In contrast to the southern Mozambique aggregation, the Mtentu Estuary aggregation seems to comprise of individuals showing fidelity to that region. The passive tracking of eight acoustically tagged individuals in the Mtentu Estuary revealed clear trends. Statistical modelling showed that estuarine presence was strongly associated with periods of cold coastal upwelling. Diel movement patterns showed that the utilisation of warm surface waters ~ 4 km upstream during the day was followed by nightly departures to the mouth or sea. Thus, it is likely that this majestic aggregation is for thermal refuge; specifically, for daily re-warming after feeding in cold waters at night. Findings from this study are of global ecological interest and have direct applications for local fisheries management and the development of sustainable eco-tourism. Protecting these vulnerable aggregations is of the utmost importance for the future of this species in southern Africa. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
Movement patterns, stock delineation and conservation of an overexploited fishery species, Lithognathus Lithognathus (Pisces: Sparidae)
- Authors: Bennett, Rhett Hamilton
- Date: 2012
- Subjects: Reef fishes -- Behavior , Endangered species -- South Africa , Fish stock assessment -- South Africa , Fishery management -- South Africa , Fish communities -- South Africa , Sparidae , Lithognathus , Lithognathus -- Growth
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5374 , http://hdl.handle.net/10962/d1015709
- Description: White steenbras Lithognathus lithognathus (Pisces: Sparidae) has been a major target species of numerous fisheries in South Africa, since the late 19th century. Historically, it contributed substantially to annual catches in commercial net fisheries, and became dominant in recreational shore catches in the latter half of the 20th century. However, overexploitation in both sectors resulted in severe declines in abundance. The ultimate collapse of the stock by the end of the last century, and the failure of traditional management measures to protect the species indicate that a new management approach for this species is necessary. The species was identified as a priority for research, management and conservation in a National Linefish Status Report. Despite knowledge on aspects of its biology and life history, little is known about juvenile habitat use patterns, home range dynamics and movement behaviour in estuaries. Similarly, the movement and migration of larger juveniles and adults in the marine environment are poorly understood. Furthermore, there is a complete lack of information on its genetic stock structure. Such information is essential for effective management of a fishery species. This thesis aimed to address the gaps in the understanding of white steenbras movement patterns and genetic stock structure, and provide an assessment of its current conservation status. The study adopted a multidisciplinary approach, incorporating a range of methods and drawing on available information, including published literature, unpublished reports and data from long-term monitoring programmes. Acoustic telemetry, conducted in a range of estuaries, showed high site fidelity, restricted area use, small home ranges relative to the size of the estuary, and a high level of residency within estuaries at the early juvenile life stage. Behaviour within estuaries was dominated by station-keeping, superimposed by a strong diel behaviour, presumably based on feeding and/or predator avoidance, with individuals entering the shallow littoral zone at night to feed, and seeking refuge in the deeper channel areas during the daytime. Conventional dart tagging and recapture data from four ongoing, long-term coastal fish tagging projects, spread throughout the distribution of this species, indicated high levels of residency in the surf zone at the late juvenile and sub-adult life stages. Consequently, juvenile and sub-adult white steenbras are vulnerable to localised depletion, although they can be effectively protected by suitably positioned estuarine protected areas (EPAs) and marine protected areas (MPAs), respectively. It has been hypothesized that adult white steenbras undertake large-scale coastal migrations between summer aggregation areas and winter spawning grounds. The scale of observed coastal movements was correlated with fish size (and age), with larger fish undertaking considerably longer-distance coastal movements than smaller individuals, supporting this hypothesis. Given the migratory behaviour of adults, and indications that limited spawning habitat exists, MPAs designed to protect white steenbras during the adult life stage should encompass all known spawning aggregation sites. The fishery is plagued by problems such as low compliance and low enforcement capacity, and alternative management measures, such as seasonal closure, need to be evaluated. Despite considerable conventional dart tagging effort around the coastline (5 782 fish tagged) with 292 recaptures there remains a lack of empirical evidence of fish migrating long distances (> 600 km) between aggregation and spawning areas. This uncertainty in the level of connectivity among coastal regions was addressed using mitochondrial DNA sequencing and genotyping of microsatellite repeat loci in the nuclear genome, which showed no evidence of major geographic barriers to gene flow in this species. Samples collected throughout the white steenbras core distribution showed high genetic diversity, low genetic differentiation and no evidence of isolation by distance or localised spawning. Although historically dominant in several fisheries, analysis of long-term commercial and recreational catch data for white steenbras indicated considerable declines and ultimately stock collapse. Improved catch-per-unit-effort in two large MPAs subsequent to closure confirmed that MPAs can be effective for the protection of white steenbras. However, the current MPA network encompasses a low proportion of sandy shoreline, for which white steenbras exhibits an affinity. Many MPAs do not prohibit recreational shore angling, which currently accounts for the greatest proportion of the total annual catch. Furthermore, EPAs within the juvenile distribution protect a negligible proportion of the total available surface area of estuaries – habitat on which white steenbras is wholly dependent. Despite some evidence of recent increases in abundance in estuaries and the surf zone in certain areas, white steenbras meets the criteria for “Endangered” on the IUCN Red List of Threatened Species, and for “Protected species” status on the National Environmental Management: Biodiversity Act of South Africa. The species requires improved management, with consideration for its life-history style, estuarine dependency, surf zone residency, predictable spawning migrations and its poor conservation status. The multidisciplinary approach provides valuable information towards an improved scientific basis for the management of white steenbras and a framework for research that can be adopted for other overexploited, estuarine-associated coastal fishery species.
- Full Text:
- Date Issued: 2012
- Authors: Bennett, Rhett Hamilton
- Date: 2012
- Subjects: Reef fishes -- Behavior , Endangered species -- South Africa , Fish stock assessment -- South Africa , Fishery management -- South Africa , Fish communities -- South Africa , Sparidae , Lithognathus , Lithognathus -- Growth
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5374 , http://hdl.handle.net/10962/d1015709
- Description: White steenbras Lithognathus lithognathus (Pisces: Sparidae) has been a major target species of numerous fisheries in South Africa, since the late 19th century. Historically, it contributed substantially to annual catches in commercial net fisheries, and became dominant in recreational shore catches in the latter half of the 20th century. However, overexploitation in both sectors resulted in severe declines in abundance. The ultimate collapse of the stock by the end of the last century, and the failure of traditional management measures to protect the species indicate that a new management approach for this species is necessary. The species was identified as a priority for research, management and conservation in a National Linefish Status Report. Despite knowledge on aspects of its biology and life history, little is known about juvenile habitat use patterns, home range dynamics and movement behaviour in estuaries. Similarly, the movement and migration of larger juveniles and adults in the marine environment are poorly understood. Furthermore, there is a complete lack of information on its genetic stock structure. Such information is essential for effective management of a fishery species. This thesis aimed to address the gaps in the understanding of white steenbras movement patterns and genetic stock structure, and provide an assessment of its current conservation status. The study adopted a multidisciplinary approach, incorporating a range of methods and drawing on available information, including published literature, unpublished reports and data from long-term monitoring programmes. Acoustic telemetry, conducted in a range of estuaries, showed high site fidelity, restricted area use, small home ranges relative to the size of the estuary, and a high level of residency within estuaries at the early juvenile life stage. Behaviour within estuaries was dominated by station-keeping, superimposed by a strong diel behaviour, presumably based on feeding and/or predator avoidance, with individuals entering the shallow littoral zone at night to feed, and seeking refuge in the deeper channel areas during the daytime. Conventional dart tagging and recapture data from four ongoing, long-term coastal fish tagging projects, spread throughout the distribution of this species, indicated high levels of residency in the surf zone at the late juvenile and sub-adult life stages. Consequently, juvenile and sub-adult white steenbras are vulnerable to localised depletion, although they can be effectively protected by suitably positioned estuarine protected areas (EPAs) and marine protected areas (MPAs), respectively. It has been hypothesized that adult white steenbras undertake large-scale coastal migrations between summer aggregation areas and winter spawning grounds. The scale of observed coastal movements was correlated with fish size (and age), with larger fish undertaking considerably longer-distance coastal movements than smaller individuals, supporting this hypothesis. Given the migratory behaviour of adults, and indications that limited spawning habitat exists, MPAs designed to protect white steenbras during the adult life stage should encompass all known spawning aggregation sites. The fishery is plagued by problems such as low compliance and low enforcement capacity, and alternative management measures, such as seasonal closure, need to be evaluated. Despite considerable conventional dart tagging effort around the coastline (5 782 fish tagged) with 292 recaptures there remains a lack of empirical evidence of fish migrating long distances (> 600 km) between aggregation and spawning areas. This uncertainty in the level of connectivity among coastal regions was addressed using mitochondrial DNA sequencing and genotyping of microsatellite repeat loci in the nuclear genome, which showed no evidence of major geographic barriers to gene flow in this species. Samples collected throughout the white steenbras core distribution showed high genetic diversity, low genetic differentiation and no evidence of isolation by distance or localised spawning. Although historically dominant in several fisheries, analysis of long-term commercial and recreational catch data for white steenbras indicated considerable declines and ultimately stock collapse. Improved catch-per-unit-effort in two large MPAs subsequent to closure confirmed that MPAs can be effective for the protection of white steenbras. However, the current MPA network encompasses a low proportion of sandy shoreline, for which white steenbras exhibits an affinity. Many MPAs do not prohibit recreational shore angling, which currently accounts for the greatest proportion of the total annual catch. Furthermore, EPAs within the juvenile distribution protect a negligible proportion of the total available surface area of estuaries – habitat on which white steenbras is wholly dependent. Despite some evidence of recent increases in abundance in estuaries and the surf zone in certain areas, white steenbras meets the criteria for “Endangered” on the IUCN Red List of Threatened Species, and for “Protected species” status on the National Environmental Management: Biodiversity Act of South Africa. The species requires improved management, with consideration for its life-history style, estuarine dependency, surf zone residency, predictable spawning migrations and its poor conservation status. The multidisciplinary approach provides valuable information towards an improved scientific basis for the management of white steenbras and a framework for research that can be adopted for other overexploited, estuarine-associated coastal fishery species.
- Full Text:
- Date Issued: 2012
Movements of sub-adult sicklefin lemon sharks Negaprion acutidens in a remote Indian Ocean atoll
- Authors: Filmalter, John David
- Date: 2012
- Subjects: Silky shark , Silky shark -- Habitat , Sharks -- Amirante Islands (Seychelles)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5383 , http://hdl.handle.net/10962/d1018229
- Description: The sicklefin lemon shark Negaprion acutidens is a large-bodied (> 3m) coastal shark species, widely distributed in tropical and sub-tropical Indo-Pacific waters. Despite its large size and wide distribution, very little is known about its movement behaviour throughout ontogeny. The primary aim of this thesis was to gain an understanding of the movements of sub-adult N. acutidens, in and around the St. Joseph Atoll, Republic of Seychelles, to facilitate the effective conservation of this vulnerable species. A total of 22 sharks (139 – 202 cm TL) were equipped with coded acoustic transmitters and passively monitored using moored acoustic receivers for a period of 20 month from March 2009 to October 2010. The use of passive acoustic telemetry arrays to study behavioural ecology has increased in popularity in recent years and been successfully applied to study a host of teleost and elasmobranch species in a diversity of habitats, ranging from sheltered estuaries to the offshore pelagic environment. However, the practicalities of designing an effective network of receivers to optimally monitor animal movements can be challenging. In this study the receiver array was optimised through a series of incremental steps to achieve an efficient design that allowed for the specific objectives to be addressed. The specific objectives of this study were to i) gain an understanding of the long term space use patterns and site fidelity of sub-adult N. acutidens within degree of use of the St. Joseph Atoll lagoon and surrounding habitats, and ii) investigate their short term behavioural patterns in response to natural rhythmic cycles. The important role the atoll plays in the sub-adult stage of this species was demonstrated by the very low numbers of detections outside the atoll compared to the very large numbers of detections inside the atoll. Over the course of a year the tagged sharks showed a high degree of site fidelity to the atoll, with 79 – 100% of the individuals detected during each month and 50% being detected on a near daily basis. This result provides testimony of the nursery role of the atoll and importance of these habitats in the early life history for this species. Individual area use was generally found to be restricted to the eastern part of the atoll incorporating a portion of the central deep lagoon and a nearby adjacent area of the sand flats. The movements of sub-adult N. acutidens on and off of the shallow flats surrounding the central lagoon (likely for foraging) were found to be strongly influenced by the tidal height and the diel cycle. Tagged sharks were found to utilise the flats more regularly when the tidal height was greater than 90 cm and particularly more so during the night and early morning than during daylight times. The combined results of this study expose the vulnerability of this species to rapid local depletion. Similarly, the effectiveness of spatial management measures, such as no-take marine protected areas is highlighted as an efficient tool for the future conservation of this species. In the St. Joseph Atoll in particular, the use of a multi-levelled protection approach, where the eastern portion on the atoll is completely restricted while the remaining area is utilized for non-consumptive tourism activities, could be highly effective. Future research should investigate changes in area use throughout the ontogeny of this species as well improve the understanding of the breeding site fidelity and population size of reproductive females using the St. Joseph Atoll.
- Full Text:
- Date Issued: 2012
- Authors: Filmalter, John David
- Date: 2012
- Subjects: Silky shark , Silky shark -- Habitat , Sharks -- Amirante Islands (Seychelles)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5383 , http://hdl.handle.net/10962/d1018229
- Description: The sicklefin lemon shark Negaprion acutidens is a large-bodied (> 3m) coastal shark species, widely distributed in tropical and sub-tropical Indo-Pacific waters. Despite its large size and wide distribution, very little is known about its movement behaviour throughout ontogeny. The primary aim of this thesis was to gain an understanding of the movements of sub-adult N. acutidens, in and around the St. Joseph Atoll, Republic of Seychelles, to facilitate the effective conservation of this vulnerable species. A total of 22 sharks (139 – 202 cm TL) were equipped with coded acoustic transmitters and passively monitored using moored acoustic receivers for a period of 20 month from March 2009 to October 2010. The use of passive acoustic telemetry arrays to study behavioural ecology has increased in popularity in recent years and been successfully applied to study a host of teleost and elasmobranch species in a diversity of habitats, ranging from sheltered estuaries to the offshore pelagic environment. However, the practicalities of designing an effective network of receivers to optimally monitor animal movements can be challenging. In this study the receiver array was optimised through a series of incremental steps to achieve an efficient design that allowed for the specific objectives to be addressed. The specific objectives of this study were to i) gain an understanding of the long term space use patterns and site fidelity of sub-adult N. acutidens within degree of use of the St. Joseph Atoll lagoon and surrounding habitats, and ii) investigate their short term behavioural patterns in response to natural rhythmic cycles. The important role the atoll plays in the sub-adult stage of this species was demonstrated by the very low numbers of detections outside the atoll compared to the very large numbers of detections inside the atoll. Over the course of a year the tagged sharks showed a high degree of site fidelity to the atoll, with 79 – 100% of the individuals detected during each month and 50% being detected on a near daily basis. This result provides testimony of the nursery role of the atoll and importance of these habitats in the early life history for this species. Individual area use was generally found to be restricted to the eastern part of the atoll incorporating a portion of the central deep lagoon and a nearby adjacent area of the sand flats. The movements of sub-adult N. acutidens on and off of the shallow flats surrounding the central lagoon (likely for foraging) were found to be strongly influenced by the tidal height and the diel cycle. Tagged sharks were found to utilise the flats more regularly when the tidal height was greater than 90 cm and particularly more so during the night and early morning than during daylight times. The combined results of this study expose the vulnerability of this species to rapid local depletion. Similarly, the effectiveness of spatial management measures, such as no-take marine protected areas is highlighted as an efficient tool for the future conservation of this species. In the St. Joseph Atoll in particular, the use of a multi-levelled protection approach, where the eastern portion on the atoll is completely restricted while the remaining area is utilized for non-consumptive tourism activities, could be highly effective. Future research should investigate changes in area use throughout the ontogeny of this species as well improve the understanding of the breeding site fidelity and population size of reproductive females using the St. Joseph Atoll.
- Full Text:
- Date Issued: 2012
Nutrient digestibility in South African abalone (Haliotis Midae L.)
- Authors: Sales, James
- Date: 2002
- Subjects: Abalones -- Digestion Abalones -- Nutrition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5305 , http://hdl.handle.net/10962/d1005150
- Description: The evaluation of potential alternative protein sources for the formulation of least-cost optimal diets to satisfy the nutrient requirements of South African abalone (Haliotis midae) has been hampered by the absence of a suitable, practical, replicable and reliable digestibility technique. A suitable lowcost faeces collection technique was developed in this study to obtain suitable quantities of excreta for analysis from this species. Acid-insoluble ash was identified as a reliable, replicable and safe internal marker in comparison to chromic oxide and crude fibre for use in nutrient digestibility studies with H. midae. This was validated by the consistency and repeatability of the results and by comparison to total collection of faeces. The traditional substitution method used in digestibility studies with fish to evaluate protein digestibility of feed ingredients was found to be unsuitable for H. midae. Apparent protein digestibility values exceeding 100 % derived through this method could be attributed to associative effects between feed ingredients, differential diet and faecal nutrient leaching, and mathematical artifacts in calculations when using substitution versus single protein diets. An ingredient particle size of less than 450 μm in comparison to particle size classes of above 450 μm was shown to enhance nutrient (dry matter, organic matter, protein, fat) digestibility and minimise dry matter leaching from diets. The dietary inclusion level of both pre-gelatinised maize starch and a-cellulose did not influence (P > 0.05) apparent nutrient (protein, fat, fiber, starch) digestibility. Using the above digestibility protocol amino acid availability of all plants ingredients currently used in the South African animal industry was evaluated for H. midae. Soybean meal (96.86 %) and lupins (96.51 %) presented the highest apparent mean amino acid availability of all plant protein ingredients evaluated with H. midae. Canola meal (94.21 %), faba beans (92.87 %) sunflower meal (92.77 %), peanut meal (87.39 %) and cottonseed meal (85.15 %) presented higher apparent mean amino acid availability values than fish meal (82.75 %). Apparent protein digestibility was highly correlated (r = 0.99) with mean apparent amino acid availability, while true amino acid availability was 1.88 % units higher than apparent amino acid availability for all ingredients tested. Predicted apparent protein digestibility in compound diets was within 1.1-6.5 % of determined values. Calcium phosphate mono dibasic presented the lowest (P < 0.05) dietary phosphorus leaching (51.51 % maximum) and highest apparent phosphorus digestibility (66.27 %) in comparison to other inorganic phosphorus sources. Based on the method of direct experimentation to determine the optimal dietary protein level using graded levels of dietary protein 28.1-35.9 % dietary protein from good quality sources is recommended for maximum growth of juvenile H. midae. This study provides a scientifically sound research tool including a faecal collection technique, suitable marker and assay technique that could be use in further studies to improve least-cost diet formulation for H. midae. Future nutritional studies in H. midae should primarily concentrate on reducing dietary nutrient leaching and improving the intake of nutrients in order to properly evaluate responses of this species to different dietary regimes.
- Full Text:
- Date Issued: 2002
- Authors: Sales, James
- Date: 2002
- Subjects: Abalones -- Digestion Abalones -- Nutrition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5305 , http://hdl.handle.net/10962/d1005150
- Description: The evaluation of potential alternative protein sources for the formulation of least-cost optimal diets to satisfy the nutrient requirements of South African abalone (Haliotis midae) has been hampered by the absence of a suitable, practical, replicable and reliable digestibility technique. A suitable lowcost faeces collection technique was developed in this study to obtain suitable quantities of excreta for analysis from this species. Acid-insoluble ash was identified as a reliable, replicable and safe internal marker in comparison to chromic oxide and crude fibre for use in nutrient digestibility studies with H. midae. This was validated by the consistency and repeatability of the results and by comparison to total collection of faeces. The traditional substitution method used in digestibility studies with fish to evaluate protein digestibility of feed ingredients was found to be unsuitable for H. midae. Apparent protein digestibility values exceeding 100 % derived through this method could be attributed to associative effects between feed ingredients, differential diet and faecal nutrient leaching, and mathematical artifacts in calculations when using substitution versus single protein diets. An ingredient particle size of less than 450 μm in comparison to particle size classes of above 450 μm was shown to enhance nutrient (dry matter, organic matter, protein, fat) digestibility and minimise dry matter leaching from diets. The dietary inclusion level of both pre-gelatinised maize starch and a-cellulose did not influence (P > 0.05) apparent nutrient (protein, fat, fiber, starch) digestibility. Using the above digestibility protocol amino acid availability of all plants ingredients currently used in the South African animal industry was evaluated for H. midae. Soybean meal (96.86 %) and lupins (96.51 %) presented the highest apparent mean amino acid availability of all plant protein ingredients evaluated with H. midae. Canola meal (94.21 %), faba beans (92.87 %) sunflower meal (92.77 %), peanut meal (87.39 %) and cottonseed meal (85.15 %) presented higher apparent mean amino acid availability values than fish meal (82.75 %). Apparent protein digestibility was highly correlated (r = 0.99) with mean apparent amino acid availability, while true amino acid availability was 1.88 % units higher than apparent amino acid availability for all ingredients tested. Predicted apparent protein digestibility in compound diets was within 1.1-6.5 % of determined values. Calcium phosphate mono dibasic presented the lowest (P < 0.05) dietary phosphorus leaching (51.51 % maximum) and highest apparent phosphorus digestibility (66.27 %) in comparison to other inorganic phosphorus sources. Based on the method of direct experimentation to determine the optimal dietary protein level using graded levels of dietary protein 28.1-35.9 % dietary protein from good quality sources is recommended for maximum growth of juvenile H. midae. This study provides a scientifically sound research tool including a faecal collection technique, suitable marker and assay technique that could be use in further studies to improve least-cost diet formulation for H. midae. Future nutritional studies in H. midae should primarily concentrate on reducing dietary nutrient leaching and improving the intake of nutrients in order to properly evaluate responses of this species to different dietary regimes.
- Full Text:
- Date Issued: 2002
On the underwater visual census of Western Indian Ocean coral reef fishes
- Authors: Wartenberg, Reece
- Date: 2012
- Subjects: Coral reef fishes -- Africa, Southern , Coral reef fishes -- Indian Ocean , Coral reef fishes -- Behavior , Fish communities -- Africa, Southern , Fish communities -- Indian Ocean , Groundfishes -- Africa, Southern , Groundfishes -- Indian Ocean , Groundfishes -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5308 , http://hdl.handle.net/10962/d1005153 , Coral reef fishes -- Africa, Southern , Coral reef fishes -- Indian Ocean , Coral reef fishes -- Behavior , Fish communities -- Africa, Southern , Fish communities -- Indian Ocean , Groundfishes -- Africa, Southern , Groundfishes -- Indian Ocean , Groundfishes -- Behavior
- Description: This study conducted the first high-resolution investigation of the ichthyofaunal assemblages on a high-latitude coral reef in the Western Indian Ocean (WIO). Two-Mile reef, in South Africa, is a large, accessible patch-reef, and was selected as a candidate study area. Although the effect of season in structuring coral reef fish communities is most-often overlooked, the relationship between these fish communities and their habitat structure has been investigated. In South Africa, however, neither of these potential community-level drivers has been explored. As coral reefs worldwide are faced with high levels of usage pressure, nondestructive underwater visual census (UVC) techniques were identified as the most appropriate survey methods. This study had two primary aims that were; (1) to identify the most suitable technique for the UVC of coral reef fishes, and to test variations of the selected technique for appropriateness to implementation in long-term monitoring programs, and (2) to determine if possible changes to ichthyofaunal community structure could be related to trends in season and/or habitat characteristics. A review of the literature indicated that the most appropriate UVC method for surveying epibenthic coral reef fishes is underwater transecting. To compare the traditional slate-based transects to variations that implement digital image technology, slate transects were compared to a first-attempt digital photographic transect technique, and digital videographic transects. Videographic transects produced the most favourable species richness, abundance, and standard deviations of the three techniques. Diversity was not significantly different between transect techniques. The minimum required sample size was lowest for videographic transects (17 replicates), intermediate for photographic transects (27 replicates) and highest for slate transects (37 replicates). Videographic and photographic transects required greater analysis time to generate counts, but required lower observer training time. While videographic transects produced the lowest proportion of species considered unidentifiable, all three transect techniques showed similar functionality to surveying epibenthic coral reef fishes. Videographic transects were therefore identified as the most appropriate UVC technique for this study. Videographic transects at shallow (6 – 14 m), intermediate (14 – 22 m) and deep (22 – 30 m) depths in mid-winter and mid-summer, sampled a total of 41 families consisting of 209 species and 18172 individuals, dominated by pomacentrids in abundance and labrids in richness. The fish assemblages on Two-Mile Reef were found to be similar in composition to lower-latitude WIO reefs. Overall ichthyofaunal abundance and richness was significantly higher in summer than in winter, and was higher at shallow sites than at intermediate and deep sites. A multivariate approach confirmed differences between seasons at shallow depths but not between seasons at intermediate and deep depths. The fish assemblages on Two-Mile Reef can therefore be described as being comprised of four relatively distinct communities: a shallow, winter community; a shallow, summer community; a year-round intermediate community; and a year-round deep community. The distributions of discriminating species indicated that high abundances of the algal-feeding pomacentrids are observed only at shallow and intermediate sites while high abundances of the zooplanktivorous serranid subfamily, the Anthiinae, are observed predominantly at deep sites. Assessment of all measured supplementary variables indicated that of all factor combinations, observed patterns could be ascribed most strongly to depth. Quantification of reef characteristics indicated that as depth increases, habitat complexity decreases, benthic communities shift from dense coral domination to sparse sponge domination, and algal biomass and cover decreases. The ability of the videographic transect technique to detect changes in community structure with season and depth indicates that season and depth should be accounted for in future high-latitude ichtyofaunal surveys, and that the videographic transect technique is suitable for implementation in long-term monitoring programs on coral reefs. The similarity in fish assemblages between Two-Mile Reef and lower latitude regions suggests that the protocol for surveying epibenthic coral reef fishes, resulting from this study, is relevant throughout the continental WIO.
- Full Text:
- Date Issued: 2012
- Authors: Wartenberg, Reece
- Date: 2012
- Subjects: Coral reef fishes -- Africa, Southern , Coral reef fishes -- Indian Ocean , Coral reef fishes -- Behavior , Fish communities -- Africa, Southern , Fish communities -- Indian Ocean , Groundfishes -- Africa, Southern , Groundfishes -- Indian Ocean , Groundfishes -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5308 , http://hdl.handle.net/10962/d1005153 , Coral reef fishes -- Africa, Southern , Coral reef fishes -- Indian Ocean , Coral reef fishes -- Behavior , Fish communities -- Africa, Southern , Fish communities -- Indian Ocean , Groundfishes -- Africa, Southern , Groundfishes -- Indian Ocean , Groundfishes -- Behavior
- Description: This study conducted the first high-resolution investigation of the ichthyofaunal assemblages on a high-latitude coral reef in the Western Indian Ocean (WIO). Two-Mile reef, in South Africa, is a large, accessible patch-reef, and was selected as a candidate study area. Although the effect of season in structuring coral reef fish communities is most-often overlooked, the relationship between these fish communities and their habitat structure has been investigated. In South Africa, however, neither of these potential community-level drivers has been explored. As coral reefs worldwide are faced with high levels of usage pressure, nondestructive underwater visual census (UVC) techniques were identified as the most appropriate survey methods. This study had two primary aims that were; (1) to identify the most suitable technique for the UVC of coral reef fishes, and to test variations of the selected technique for appropriateness to implementation in long-term monitoring programs, and (2) to determine if possible changes to ichthyofaunal community structure could be related to trends in season and/or habitat characteristics. A review of the literature indicated that the most appropriate UVC method for surveying epibenthic coral reef fishes is underwater transecting. To compare the traditional slate-based transects to variations that implement digital image technology, slate transects were compared to a first-attempt digital photographic transect technique, and digital videographic transects. Videographic transects produced the most favourable species richness, abundance, and standard deviations of the three techniques. Diversity was not significantly different between transect techniques. The minimum required sample size was lowest for videographic transects (17 replicates), intermediate for photographic transects (27 replicates) and highest for slate transects (37 replicates). Videographic and photographic transects required greater analysis time to generate counts, but required lower observer training time. While videographic transects produced the lowest proportion of species considered unidentifiable, all three transect techniques showed similar functionality to surveying epibenthic coral reef fishes. Videographic transects were therefore identified as the most appropriate UVC technique for this study. Videographic transects at shallow (6 – 14 m), intermediate (14 – 22 m) and deep (22 – 30 m) depths in mid-winter and mid-summer, sampled a total of 41 families consisting of 209 species and 18172 individuals, dominated by pomacentrids in abundance and labrids in richness. The fish assemblages on Two-Mile Reef were found to be similar in composition to lower-latitude WIO reefs. Overall ichthyofaunal abundance and richness was significantly higher in summer than in winter, and was higher at shallow sites than at intermediate and deep sites. A multivariate approach confirmed differences between seasons at shallow depths but not between seasons at intermediate and deep depths. The fish assemblages on Two-Mile Reef can therefore be described as being comprised of four relatively distinct communities: a shallow, winter community; a shallow, summer community; a year-round intermediate community; and a year-round deep community. The distributions of discriminating species indicated that high abundances of the algal-feeding pomacentrids are observed only at shallow and intermediate sites while high abundances of the zooplanktivorous serranid subfamily, the Anthiinae, are observed predominantly at deep sites. Assessment of all measured supplementary variables indicated that of all factor combinations, observed patterns could be ascribed most strongly to depth. Quantification of reef characteristics indicated that as depth increases, habitat complexity decreases, benthic communities shift from dense coral domination to sparse sponge domination, and algal biomass and cover decreases. The ability of the videographic transect technique to detect changes in community structure with season and depth indicates that season and depth should be accounted for in future high-latitude ichtyofaunal surveys, and that the videographic transect technique is suitable for implementation in long-term monitoring programs on coral reefs. The similarity in fish assemblages between Two-Mile Reef and lower latitude regions suggests that the protocol for surveying epibenthic coral reef fishes, resulting from this study, is relevant throughout the continental WIO.
- Full Text:
- Date Issued: 2012
On the use of metabolic rate measurements to assess the stress response in juvenile spotted grunter, Pomadasys commersonnii (Haemulidae, Pisces)
- Authors: Radull, John
- Date: 2003
- Subjects: Fishes -- Metabolism Fishes -- Physiology Pomadasys -- Physiology Grunts (Fishes) -- Physiology Stress (Psychology) Stress (Physiology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5350 , http://hdl.handle.net/10962/d1007564
- Description: Quantitication of stress requires the use of a stress indicator that is easy to measure, and which can be readily interpreted in terms of the potential long-term effects to an organism. This study evaluates the suitability of metabolic rate as an indicator of the stress response in fish. By comparing the metabolic with the cortisol stress response, the most commonly used indicator of stress in fish, it was possible to assess the suitability of metabolic rate as a stress indicator. Changes in metabolic rate were used to predict the long-term effects of transport-related stressors. This study also detennined the baseline metabolic rates of the tish. The standard and the active metabolic rates of juvenile P. cummersonnii were 0.16 ± 0.02 (mean ± S.D, n = 6) mg O₂g⁻¹h⁻¹, and 0.56 ± 0.04 mg O₂g⁻¹h⁻¹, respectively, whereas the routine metabolic rate for the fish was 0.25 ± 0.03 mg O₂g⁻¹h¹. The relationship between metabolic rate and body weight was described by the equation ϺO₂ = 0.64 W⁻°·³⁸. 24-h oxygen consumption measurements showed that juvenile P. commersonnii exhibited diel rhythmicity in oxygen consumption rate, the higher rates occurring at night and the lower rates during the daytime. The higher nocturnal metabolic activity may have been due to increased activity induced by an endogenous rhythm related to feeding. Diel rhythmicity has direct implications for the measurement of baseline metabolic rates since it could result in overestimation or underestimation of these rates. 24-h continuous oxygen consumption measurements enabled the detection of the rhythmicity in oxygen consumption rate, and thereby ensured a greater degree of accuracy in the estimation of these parameters. The metabolic stress response in juvenile P. commersonnii was best described by the equation, y = -0.0013 x² + 0.0364 x ÷ 0.3052, where x = time after application of stressor, and y = oxygen consumption rate. Using the derivative of this equation, the metabolic stress response was estimated to peak approximately 14 min after application of a simulated capture and handling stressor. Oxygen consumption increased by about 300 % as a result of the stress. Approximately 15 min after application of a similar stressor, plasma cortisol levels in stressed fish was 200 % higher than baseline levels. However, cortisol levels in fish sampled 30 min after the disturbance was similar to the baseline cortisol levels, indicating that full recovery had occurred. Although the patterns in the metabolic and cortisol stress responses were similar, metabolic rate could be measured continuously, thereby ensuring accurate interpretation of the data. Furthermore, increases in metabolic rate during the stress response are a culmination of physiological events from the primary to the tertiary levels of biological organization and are, therefore, easier to interpret in terms of long-term effects on the fish. Different transportation procedures elicited variable degrees of stress in juvenile P. commersonnii. The cost of metabolism attributed to the effects of capture and handling was twice as much as that attributed to acute temperature elevation. Acute temperature decrease resulted in a signiticant reduction in the oxygen consumption rate (ANOVA, P < 0.05). Oxygen consumption by the fish was not affected by fish density (ANOVA: F = 2.002, P = 0.5), or by oxygen depletion at dissolved oxygen concentrations above the critical level. Below this level, however, oxygen consumption decreased linearly with further decrease in dissolved oxygen concentration. These results showed that the highest energetic cost to juvenile P. commersonnii was incurred as a result of capture and handling. The results also showed that by subjecting fish to different stressors, it was possible to categorize them according to their relative metabolic costs to the fish. At 25º C, the effective concentration of 2-phenoxyethanol to fully anaesthetize (Stage IV, McFarland 1960) juvenile P. commersonnii was 0.4 ml l⁻¹ and the most appropriate concentration for deep sedation (Stage II, McFarland 1960) of the fish for at least 24 h was 0.2 ml l⁻¹. A maximum of 3 minutes was required by the fish to recover from the effects of the anaesthetic. There was no correlation between fish weight and the rate of induction of anaesthesia (r² = 0.001, p = 0.3). At the peak of the metabolic stress response, oxygen consumption was twice as high in the un-anaesthetized fish compared to the fish anaesthetized after the application of the simulated capture and handling stressor, suggesting that anaesthetization with 2-phenoxyethanol may have reduced the effect of the disturbance on the fish. Similar oxygen consumption rates for the fish anaesthetized prior to capture and the non-stressed fish suggested that the increases in metabolic rate could be linked to the struggling associated with attempts by fish to escape from the perceived stressor. Anaesthetization of juvenile P. commersonnii with 0.3 ml l⁻¹ 2-phenoxyethanol resulted in a more than 200 % increase in plasma cortisol concentration. The elevated levels of plasma cortisol in the anaesthetized fish suggested a manifestation of 2-phenoxyethanol as a stressor. At the time of capture, cortisol levels in fish that were anaesthetized prior to capture were the same as those measured in the disturbed fish at the peak of the stress response (ANOVA, p = 0.95), suggesting that the anaesthetized fish were already experiencing considerable stress at the time they were captured. Undisturbed juvenile P. commersonnii that were anaesthetized for 1 h also had cortisol levels that were five times higher than those measured in undisturbed-unanaesthetized fish, indicating that the duration of exposure to the anaesthetic had a significant effect on plasma cortisol levels. The results presented in this study demonstrate the usefulness of metabolic rate as an indicator of acute stress in fish. This was achieved by comparing the metabolic and the cortisol stress responses. The ease and accuracy with which oxygen consumption of fish could be measured made it possible to measure the stress response more accurately than by plasma cortisol concentration. It was also possible to monitor metabolic rate continuously over a long duration using polarographic oxygen sensors, thus enabling a better evaluation of the stress response. These results, thus, suggest that metabolic rate measurements could be a more practical way to quantify the effects of acute stressors on juvenile fishes. By detailing the profile of the metabolic stress response in P. commersonnii, this study makes a contribution towards understanding the physiological effects of stress in fishes. The study also contributes towards the quantification of baseline metabolic rates of this species under captivity. This study also contributes towards understanding the effects of 2-phenoxyethanol on the stress physiology of fish. By anaesthetizing fish under different conditions of stress, it was possible to evaluate the effect of 2-phenoxyethanol on the metabolic stress response. The ability of 2-phenoxyethanol to reduce physical activity of the fish, and thereby reduce the impact of acute stress on the metabolic stress response, makes it a good agent for the mitigation of stress during the capture and handling of fish. However, the increase in plasma cortisol concentration during prolonged anaesthetization using this drug suggests that the anaesthetic might be a stressor to fish and may, therefore, not be suitable for long-term sedation.
- Full Text:
- Date Issued: 2003
- Authors: Radull, John
- Date: 2003
- Subjects: Fishes -- Metabolism Fishes -- Physiology Pomadasys -- Physiology Grunts (Fishes) -- Physiology Stress (Psychology) Stress (Physiology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5350 , http://hdl.handle.net/10962/d1007564
- Description: Quantitication of stress requires the use of a stress indicator that is easy to measure, and which can be readily interpreted in terms of the potential long-term effects to an organism. This study evaluates the suitability of metabolic rate as an indicator of the stress response in fish. By comparing the metabolic with the cortisol stress response, the most commonly used indicator of stress in fish, it was possible to assess the suitability of metabolic rate as a stress indicator. Changes in metabolic rate were used to predict the long-term effects of transport-related stressors. This study also detennined the baseline metabolic rates of the tish. The standard and the active metabolic rates of juvenile P. cummersonnii were 0.16 ± 0.02 (mean ± S.D, n = 6) mg O₂g⁻¹h⁻¹, and 0.56 ± 0.04 mg O₂g⁻¹h⁻¹, respectively, whereas the routine metabolic rate for the fish was 0.25 ± 0.03 mg O₂g⁻¹h¹. The relationship between metabolic rate and body weight was described by the equation ϺO₂ = 0.64 W⁻°·³⁸. 24-h oxygen consumption measurements showed that juvenile P. commersonnii exhibited diel rhythmicity in oxygen consumption rate, the higher rates occurring at night and the lower rates during the daytime. The higher nocturnal metabolic activity may have been due to increased activity induced by an endogenous rhythm related to feeding. Diel rhythmicity has direct implications for the measurement of baseline metabolic rates since it could result in overestimation or underestimation of these rates. 24-h continuous oxygen consumption measurements enabled the detection of the rhythmicity in oxygen consumption rate, and thereby ensured a greater degree of accuracy in the estimation of these parameters. The metabolic stress response in juvenile P. commersonnii was best described by the equation, y = -0.0013 x² + 0.0364 x ÷ 0.3052, where x = time after application of stressor, and y = oxygen consumption rate. Using the derivative of this equation, the metabolic stress response was estimated to peak approximately 14 min after application of a simulated capture and handling stressor. Oxygen consumption increased by about 300 % as a result of the stress. Approximately 15 min after application of a similar stressor, plasma cortisol levels in stressed fish was 200 % higher than baseline levels. However, cortisol levels in fish sampled 30 min after the disturbance was similar to the baseline cortisol levels, indicating that full recovery had occurred. Although the patterns in the metabolic and cortisol stress responses were similar, metabolic rate could be measured continuously, thereby ensuring accurate interpretation of the data. Furthermore, increases in metabolic rate during the stress response are a culmination of physiological events from the primary to the tertiary levels of biological organization and are, therefore, easier to interpret in terms of long-term effects on the fish. Different transportation procedures elicited variable degrees of stress in juvenile P. commersonnii. The cost of metabolism attributed to the effects of capture and handling was twice as much as that attributed to acute temperature elevation. Acute temperature decrease resulted in a signiticant reduction in the oxygen consumption rate (ANOVA, P < 0.05). Oxygen consumption by the fish was not affected by fish density (ANOVA: F = 2.002, P = 0.5), or by oxygen depletion at dissolved oxygen concentrations above the critical level. Below this level, however, oxygen consumption decreased linearly with further decrease in dissolved oxygen concentration. These results showed that the highest energetic cost to juvenile P. commersonnii was incurred as a result of capture and handling. The results also showed that by subjecting fish to different stressors, it was possible to categorize them according to their relative metabolic costs to the fish. At 25º C, the effective concentration of 2-phenoxyethanol to fully anaesthetize (Stage IV, McFarland 1960) juvenile P. commersonnii was 0.4 ml l⁻¹ and the most appropriate concentration for deep sedation (Stage II, McFarland 1960) of the fish for at least 24 h was 0.2 ml l⁻¹. A maximum of 3 minutes was required by the fish to recover from the effects of the anaesthetic. There was no correlation between fish weight and the rate of induction of anaesthesia (r² = 0.001, p = 0.3). At the peak of the metabolic stress response, oxygen consumption was twice as high in the un-anaesthetized fish compared to the fish anaesthetized after the application of the simulated capture and handling stressor, suggesting that anaesthetization with 2-phenoxyethanol may have reduced the effect of the disturbance on the fish. Similar oxygen consumption rates for the fish anaesthetized prior to capture and the non-stressed fish suggested that the increases in metabolic rate could be linked to the struggling associated with attempts by fish to escape from the perceived stressor. Anaesthetization of juvenile P. commersonnii with 0.3 ml l⁻¹ 2-phenoxyethanol resulted in a more than 200 % increase in plasma cortisol concentration. The elevated levels of plasma cortisol in the anaesthetized fish suggested a manifestation of 2-phenoxyethanol as a stressor. At the time of capture, cortisol levels in fish that were anaesthetized prior to capture were the same as those measured in the disturbed fish at the peak of the stress response (ANOVA, p = 0.95), suggesting that the anaesthetized fish were already experiencing considerable stress at the time they were captured. Undisturbed juvenile P. commersonnii that were anaesthetized for 1 h also had cortisol levels that were five times higher than those measured in undisturbed-unanaesthetized fish, indicating that the duration of exposure to the anaesthetic had a significant effect on plasma cortisol levels. The results presented in this study demonstrate the usefulness of metabolic rate as an indicator of acute stress in fish. This was achieved by comparing the metabolic and the cortisol stress responses. The ease and accuracy with which oxygen consumption of fish could be measured made it possible to measure the stress response more accurately than by plasma cortisol concentration. It was also possible to monitor metabolic rate continuously over a long duration using polarographic oxygen sensors, thus enabling a better evaluation of the stress response. These results, thus, suggest that metabolic rate measurements could be a more practical way to quantify the effects of acute stressors on juvenile fishes. By detailing the profile of the metabolic stress response in P. commersonnii, this study makes a contribution towards understanding the physiological effects of stress in fishes. The study also contributes towards the quantification of baseline metabolic rates of this species under captivity. This study also contributes towards understanding the effects of 2-phenoxyethanol on the stress physiology of fish. By anaesthetizing fish under different conditions of stress, it was possible to evaluate the effect of 2-phenoxyethanol on the metabolic stress response. The ability of 2-phenoxyethanol to reduce physical activity of the fish, and thereby reduce the impact of acute stress on the metabolic stress response, makes it a good agent for the mitigation of stress during the capture and handling of fish. However, the increase in plasma cortisol concentration during prolonged anaesthetization using this drug suggests that the anaesthetic might be a stressor to fish and may, therefore, not be suitable for long-term sedation.
- Full Text:
- Date Issued: 2003
Optimisation of a sampling protocol for long-term monitoring of temperate reef fishes
- Authors: Bennett, Rhett Hamilton
- Date: 2008
- Subjects: Marine parks and reserves -- South Africa , Coastal zone management -- South Africa , Fishery management -- South Africa , Reef fishes -- South Africa , Fish communities -- South Africa , Fish stock assessment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5309 , http://hdl.handle.net/10962/d1005154 , Marine parks and reserves -- South Africa , Coastal zone management -- South Africa , Fishery management -- South Africa , Reef fishes -- South Africa , Fish communities -- South Africa , Fish stock assessment
- Description: Marine Protected Areas (MPAs), the Ecosystem Approach to Fisheries management (EAF) and Integrated Coastal Management (ICM) have been identified as possible alternatives to traditional linefish management measures, which have largely failed. Monitoring and assessment of fish communities on a long-term basis is necessary, and will provide a means to evaluate the effectiveness of such management measures. Therefore, standardised protocols and optimal sampling methods for long-term monitoring (LTM) and assessment of coastal fish communities are essential. This study aimed to identify suitable methods and develop a protocol for assessment of inshore reef fish communities. A suitable location for evaluation of proposed methods was identified in the warm temperate biogeographical region of South Africa, encompassing the well-established Tsitsikamma Coastal National Park MPA and an adjacent exploited area. Chrysoblephus laticeps (roman) was identified as an indicator species for the study, as it has been well-studied and is well represented in the area. Underwater visual census (UVC) and controlled fishing were identified as suitable methods. UVC transects were found to be superior to point counts, in terms of sampling efficiency, variability, bias and required sample size. An effort of two angler hours per fishing station was shown to provide low catch variability, while at the same time a representative catch and low overall cost and required time. The methods were incorporated in a proposed sampling protocol, and evaluated. The methods were able to detect known differences between protected and exploited communities. It is recommended that LTM within protected areas, for detection of natural change, be focused on community-level indicators, while LTM in exploited areas, aimed at detection of anthropogenic change, be focused on species-level indicators. The proposed protocol with standardised methods will allow for comparisons across a network of LTM sites and provide the opportunity for a broad-scale assessment of the effects of environmental variables on reef fish stocks. The protocol developed in this study has application in other biogeographical regions in South Africa, and other parts of the world. Shift in the focus of much marine research, in South Africa and elsewhere, to LTM, highlights the relevance and timeous nature of this study.
- Full Text:
- Date Issued: 2008
- Authors: Bennett, Rhett Hamilton
- Date: 2008
- Subjects: Marine parks and reserves -- South Africa , Coastal zone management -- South Africa , Fishery management -- South Africa , Reef fishes -- South Africa , Fish communities -- South Africa , Fish stock assessment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5309 , http://hdl.handle.net/10962/d1005154 , Marine parks and reserves -- South Africa , Coastal zone management -- South Africa , Fishery management -- South Africa , Reef fishes -- South Africa , Fish communities -- South Africa , Fish stock assessment
- Description: Marine Protected Areas (MPAs), the Ecosystem Approach to Fisheries management (EAF) and Integrated Coastal Management (ICM) have been identified as possible alternatives to traditional linefish management measures, which have largely failed. Monitoring and assessment of fish communities on a long-term basis is necessary, and will provide a means to evaluate the effectiveness of such management measures. Therefore, standardised protocols and optimal sampling methods for long-term monitoring (LTM) and assessment of coastal fish communities are essential. This study aimed to identify suitable methods and develop a protocol for assessment of inshore reef fish communities. A suitable location for evaluation of proposed methods was identified in the warm temperate biogeographical region of South Africa, encompassing the well-established Tsitsikamma Coastal National Park MPA and an adjacent exploited area. Chrysoblephus laticeps (roman) was identified as an indicator species for the study, as it has been well-studied and is well represented in the area. Underwater visual census (UVC) and controlled fishing were identified as suitable methods. UVC transects were found to be superior to point counts, in terms of sampling efficiency, variability, bias and required sample size. An effort of two angler hours per fishing station was shown to provide low catch variability, while at the same time a representative catch and low overall cost and required time. The methods were incorporated in a proposed sampling protocol, and evaluated. The methods were able to detect known differences between protected and exploited communities. It is recommended that LTM within protected areas, for detection of natural change, be focused on community-level indicators, while LTM in exploited areas, aimed at detection of anthropogenic change, be focused on species-level indicators. The proposed protocol with standardised methods will allow for comparisons across a network of LTM sites and provide the opportunity for a broad-scale assessment of the effects of environmental variables on reef fish stocks. The protocol developed in this study has application in other biogeographical regions in South Africa, and other parts of the world. Shift in the focus of much marine research, in South Africa and elsewhere, to LTM, highlights the relevance and timeous nature of this study.
- Full Text:
- Date Issued: 2008
Phylogeography and conservation of a newly identified galaxiid from the Joubertina area, South Africa
- Authors: Mataruse, Gamuchirai
- Date: 2013
- Subjects: Galaxiidae -- South Africa -- Joubertina , Phylogeography -- South Africa -- Joubertina , Galaxiidae -- Conservation -- South Africa -- Joubertina , Galaxiidae -- Effect of exotic animals on -- South Africa -- Joubertina , Galaxiidae -- Effect of habitat modification on -- South Africa -- Joubertina , Galaxiidae -- Genetics -- South Africa -- Joubertina , Galaxiidae -- Variation -- South Africa -- Joubertina , Galaxiidae -- Geographical distribution -- South Africa -- Joubertina
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5199 , http://hdl.handle.net/10962/d1003050 , Galaxiidae -- South Africa -- Joubertina , Phylogeography -- South Africa -- Joubertina , Galaxiidae -- Conservation -- South Africa -- Joubertina , Galaxiidae -- Effect of exotic animals on -- South Africa -- Joubertina , Galaxiidae -- Effect of habitat modification on -- South Africa -- Joubertina , Galaxiidae -- Genetics -- South Africa -- Joubertina , Galaxiidae -- Variation -- South Africa -- Joubertina , Galaxiidae -- Geographical distribution -- South Africa -- Joubertina
- Description: The dispersal of freshwater fishes in the Cape Floristic Region of South Africa has been attributed to river capture events and confluence of rivers during sea level regression. The role of low drainage divides and inter-basin water transfers have received less attention. A unique lineage of Galaxias zebratus (hereafter the Joubertina galaxias) occurs in two currently isolated river systems, the Gamtoos and Krom. The present study mapped the distribution of the Joubertina galaxias and used mitochondrial and nuclear DNA sequences to assess the processes that could have influenced its current distribution pattern. Analyses of both mitochondrial cytochrome ♭ and nuclear (S7) sequences revealed that observed genetic differentiation cannot be explained by isolation between the Gamtoos and Krom River systems. No genetic differentiation was found between the Krom River System and the Twee River (a tributary of the Gamtoos River System). Shallow genetic differentiation (0.4% for cytochrome ♭ and 0.3% for S7) was found between the Krom and the remaining populations in the Gamtoos River System. High levels of genetic structuring were observed within the Gamtoos River System with most tributaries having one or more unique alleles. Inter-basin dispersal during pluvial periods or recent human mediated translocation seems to be the most plausible explanations for presence of the Joubertina galaxias in the Krom River System. The present study also assessed the threats and habitat preferences of the Joubertina galaxias, and an evaluation of the conservation status of this lineage was done. The Joubertina galaxias is threatened mainly by alien fish invasion, habitat loss and loss of genetic diversity due to fragmentation of its populations. Due to its very restricted geographic range, small known population sizes and the intensity of threats to this lineage’s survival, this lineage has been assessed as Endangered. The lineage has a restricted Area of Occupancy (AOO) and Extent of Occurrence (EOO). The extent of occurrence has declined in all tributaries and is continuing to decline in all except two tributaries that are secure. The lineage may have had natural fragmentation among its populations, but recent threats have completely isolated the populations. The threats affect the lineage’s survival potential in the four tributaries which have small populations that are not presently viable. The densities observed for the Joubertina galaxias ranged from 0.16 - 1.3 fish /m² and the number of mature individuals for the whole population seems to be less than 2500 mature individuals. There is therefore a need for specific conservation actions to ensure the long-term survival of this unique lineage.
- Full Text:
- Date Issued: 2013
- Authors: Mataruse, Gamuchirai
- Date: 2013
- Subjects: Galaxiidae -- South Africa -- Joubertina , Phylogeography -- South Africa -- Joubertina , Galaxiidae -- Conservation -- South Africa -- Joubertina , Galaxiidae -- Effect of exotic animals on -- South Africa -- Joubertina , Galaxiidae -- Effect of habitat modification on -- South Africa -- Joubertina , Galaxiidae -- Genetics -- South Africa -- Joubertina , Galaxiidae -- Variation -- South Africa -- Joubertina , Galaxiidae -- Geographical distribution -- South Africa -- Joubertina
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5199 , http://hdl.handle.net/10962/d1003050 , Galaxiidae -- South Africa -- Joubertina , Phylogeography -- South Africa -- Joubertina , Galaxiidae -- Conservation -- South Africa -- Joubertina , Galaxiidae -- Effect of exotic animals on -- South Africa -- Joubertina , Galaxiidae -- Effect of habitat modification on -- South Africa -- Joubertina , Galaxiidae -- Genetics -- South Africa -- Joubertina , Galaxiidae -- Variation -- South Africa -- Joubertina , Galaxiidae -- Geographical distribution -- South Africa -- Joubertina
- Description: The dispersal of freshwater fishes in the Cape Floristic Region of South Africa has been attributed to river capture events and confluence of rivers during sea level regression. The role of low drainage divides and inter-basin water transfers have received less attention. A unique lineage of Galaxias zebratus (hereafter the Joubertina galaxias) occurs in two currently isolated river systems, the Gamtoos and Krom. The present study mapped the distribution of the Joubertina galaxias and used mitochondrial and nuclear DNA sequences to assess the processes that could have influenced its current distribution pattern. Analyses of both mitochondrial cytochrome ♭ and nuclear (S7) sequences revealed that observed genetic differentiation cannot be explained by isolation between the Gamtoos and Krom River systems. No genetic differentiation was found between the Krom River System and the Twee River (a tributary of the Gamtoos River System). Shallow genetic differentiation (0.4% for cytochrome ♭ and 0.3% for S7) was found between the Krom and the remaining populations in the Gamtoos River System. High levels of genetic structuring were observed within the Gamtoos River System with most tributaries having one or more unique alleles. Inter-basin dispersal during pluvial periods or recent human mediated translocation seems to be the most plausible explanations for presence of the Joubertina galaxias in the Krom River System. The present study also assessed the threats and habitat preferences of the Joubertina galaxias, and an evaluation of the conservation status of this lineage was done. The Joubertina galaxias is threatened mainly by alien fish invasion, habitat loss and loss of genetic diversity due to fragmentation of its populations. Due to its very restricted geographic range, small known population sizes and the intensity of threats to this lineage’s survival, this lineage has been assessed as Endangered. The lineage has a restricted Area of Occupancy (AOO) and Extent of Occurrence (EOO). The extent of occurrence has declined in all tributaries and is continuing to decline in all except two tributaries that are secure. The lineage may have had natural fragmentation among its populations, but recent threats have completely isolated the populations. The threats affect the lineage’s survival potential in the four tributaries which have small populations that are not presently viable. The densities observed for the Joubertina galaxias ranged from 0.16 - 1.3 fish /m² and the number of mature individuals for the whole population seems to be less than 2500 mature individuals. There is therefore a need for specific conservation actions to ensure the long-term survival of this unique lineage.
- Full Text:
- Date Issued: 2013
Population dynamics of the raggedtooth shark (carcharias taurus) along the east coast of South Africa
- Authors: Dicken, Matthew Laurence
- Date: 2006
- Subjects: Sharks -- South Africa Shark fisheries -- South Africa Fish populations -- South Africa Sand tiger shark Fish tagging -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5310 , http://hdl.handle.net/10962/d1005155
- Description: This thesis develops the first open population model for any shark species worldwide using the Cormack-Jolly-Seber (CJS) model. In conjunction with a tagging study, five auxiliary studies were conducted to investigate stock structure, post-release mortality, tag shedding, and tag-reporting rates. The results from each of the studies were used to correct for any violations of the models assumptions to provide the first unbiased estimates of survival and abundance for the raggedtooth shark (Carcharias taurus) in South Africa. The C. taurus population exhibited complex stock structuring, by size and sex. Competitive shore anglers fished an estimated 37, 820 fishing days.year⁻¹ (95% C.I. = 28, 281 - 47, 359 days.year⁻¹) for sharks, and caught 1764 (95% C.I. = 321 – 3207) C. taurus. Although released alive, post-release mortality ranged from 3.85% for young-of-the-year sharks to 18.46% for adult sharks. Between 1984 and 2004, a total of 3471 C. taurus were tagged. In all, 302-tagged sharks (8.7%) were recaptured. Both juvenile (< 1.8 m TL) and adult sharks (> 1.8 m TL) displayed philopatric behaviour for specific parts of their ranges, including gestating and parturition areas. Significant differences were observed in the percentage of recaptures between the different tag types, tagging programs, individual taggers and capture methods used to tag sharks. The annual tag retention rate for juvenile sharks, 94.19% (95% C.I. = 80.68% - 100.00%) was significantly higher than for adult sharks, estimated at 29.00% (95% C.I. = 6.76% - 64.39%). Tag reporting rates, from fishermen varied both spatially and temporally from 0.28 (95% C.I. = 0.00 – 0.63) to 0.77 (95% C.I. = 0.56 – 0.97). Associated tag wound damage and biofouling growth indicated that B-type tags were a suitable tag type for use on C. taurus, whereas C-type tags were not. The CJS bias-adjusted estimate for juvenile survival was 0.456 (95% C.I. = 0.367 – 0.516) and for adult sharks, 0.865 (95% C.I. = 0.795 – 0.915). From 1984 to 2004 the mean bias-adjusted population size for juvenile sharks was estimated at 3506 (95% C.I. = 2433 – 4350) and for adult sharks, 5899 (95% C.I. = 7216 – 11904). Trends in abundance over the 20-year study period indicated a stable, healthy population.
- Full Text:
- Date Issued: 2006
- Authors: Dicken, Matthew Laurence
- Date: 2006
- Subjects: Sharks -- South Africa Shark fisheries -- South Africa Fish populations -- South Africa Sand tiger shark Fish tagging -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5310 , http://hdl.handle.net/10962/d1005155
- Description: This thesis develops the first open population model for any shark species worldwide using the Cormack-Jolly-Seber (CJS) model. In conjunction with a tagging study, five auxiliary studies were conducted to investigate stock structure, post-release mortality, tag shedding, and tag-reporting rates. The results from each of the studies were used to correct for any violations of the models assumptions to provide the first unbiased estimates of survival and abundance for the raggedtooth shark (Carcharias taurus) in South Africa. The C. taurus population exhibited complex stock structuring, by size and sex. Competitive shore anglers fished an estimated 37, 820 fishing days.year⁻¹ (95% C.I. = 28, 281 - 47, 359 days.year⁻¹) for sharks, and caught 1764 (95% C.I. = 321 – 3207) C. taurus. Although released alive, post-release mortality ranged from 3.85% for young-of-the-year sharks to 18.46% for adult sharks. Between 1984 and 2004, a total of 3471 C. taurus were tagged. In all, 302-tagged sharks (8.7%) were recaptured. Both juvenile (< 1.8 m TL) and adult sharks (> 1.8 m TL) displayed philopatric behaviour for specific parts of their ranges, including gestating and parturition areas. Significant differences were observed in the percentage of recaptures between the different tag types, tagging programs, individual taggers and capture methods used to tag sharks. The annual tag retention rate for juvenile sharks, 94.19% (95% C.I. = 80.68% - 100.00%) was significantly higher than for adult sharks, estimated at 29.00% (95% C.I. = 6.76% - 64.39%). Tag reporting rates, from fishermen varied both spatially and temporally from 0.28 (95% C.I. = 0.00 – 0.63) to 0.77 (95% C.I. = 0.56 – 0.97). Associated tag wound damage and biofouling growth indicated that B-type tags were a suitable tag type for use on C. taurus, whereas C-type tags were not. The CJS bias-adjusted estimate for juvenile survival was 0.456 (95% C.I. = 0.367 – 0.516) and for adult sharks, 0.865 (95% C.I. = 0.795 – 0.915). From 1984 to 2004 the mean bias-adjusted population size for juvenile sharks was estimated at 3506 (95% C.I. = 2433 – 4350) and for adult sharks, 5899 (95% C.I. = 7216 – 11904). Trends in abundance over the 20-year study period indicated a stable, healthy population.
- Full Text:
- Date Issued: 2006
Population genomics analysis of yellowfin tuna Thunnus albacares off South Africa reveals need for a shifted management boundary
- Authors: Mullins, Rachel Brenna
- Date: 2017
- Subjects: Yellowfin tuna fisheries -- South Africa -- Western Cape , Genomics , Tuna fisheries -- South Africa , Fishery management -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/57819 , vital:26992
- Description: Yellowfin tuna Thunnus albacares is a commercially and economically important fisheries species, which comprises the second largest component of South Africa’s catch of tuna and tuna-like species. Catches of the species off South Africa are treated as two discrete stocks by the two tuna Regional Fisheries Management Organisations (tRFMOs) under whose jurisdictions they fall. Individuals caught off the Western Cape, west of the boundary between the tRFMOs at 20°E, are included in assessment and management of the Atlantic Ocean yellowfin tuna stock by the International Commission for the Conservation of Atlantic Tunas (ICCAT), and those caught east of this boundary are assessed and managed as part of the Indian Ocean stock by the Indian Ocean Tuna Commission (IOTC). The boundary between these stocks is based on the confluence of the two oceans in this region and does not incorporate the population structure of species. For sustainable exploitation of fisheries resources, it is important that the definition of management stocks reflects species’ biological population structure; the fine-scale stock structure of yellowfin tuna off South Africa is therefore a research priority which this study aimed to address by means of population genomics analyses. Yellowfin tuna exhibit shallow genetic differentiation over wide geographic areas, and as such traditional population genetic approaches have limited power in resolving fishery significant population structure in the species. Herein, a population genomic approach was employed, specifically, genome-wide analysis of single nucleotide polymorphisms (SNPs) discovered using a next-generation DNA sequencing approach, to confer (i) increased statistical power to detect neutral structuring reflecting population connectivity patterns and (ii) signatures of local adaptation. The mitochondrial Control Region (mtDNA CR) was also sequenced to compare the resolving power of different approaches and to permit coalescent based analyses of the species evolutionary history in the region. Neutral SNP loci revealed significant structure within the dataset (Fst=0.0043; P<0.0001); partitioning of this differentiation within the dataset indicated significant differentiation between yellowfin tuna from the Western Cape and the Gulf of Guinea in the eastern Atlantic Ocean, with no significant differentiation between individuals from the Western Cape and Western Indian Ocean regions. This indicates two population units wherein there is a separation of the Gulf of Guinea from the remaining samples (Indian Ocean including Western Cape) that are largely derived from a single genetic population. This pattern was also supported by assignment tests. Positive outlier SNPs, exhibiting signatures of diversifying selection, suggest that individuals from these regions may be locally adapted, as well as demographically isolated. The mtDNA CR did not reveal any significant genetic structure among samples (Fst=0.0030; P=0.309), demonstrating the increased resolving power provided by population genomics approaches, but revealed signatures of historical demographic fluctuations associated with glacial cycles. Based on the findings of this study, it is suggested that yellowfin tuna caught off the Western Cape of South Africa are migrants from the Indian Ocean population, exhibiting significant genetic differentiation from the Atlantic Ocean Gulf of Guinea individuals, and should thus be included in the assessment and management of the Indian Ocean stock. It is therefore recommended that the boundary between the Atlantic and Indian Ocean yellowfin tuna stocks, under the mandates of ICCAT and the IOTC respectively, should be shifted to approximately 13.35°E to include all individuals caught in South African waters in the Indian Ocean stock.
- Full Text:
- Date Issued: 2017
- Authors: Mullins, Rachel Brenna
- Date: 2017
- Subjects: Yellowfin tuna fisheries -- South Africa -- Western Cape , Genomics , Tuna fisheries -- South Africa , Fishery management -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/57819 , vital:26992
- Description: Yellowfin tuna Thunnus albacares is a commercially and economically important fisheries species, which comprises the second largest component of South Africa’s catch of tuna and tuna-like species. Catches of the species off South Africa are treated as two discrete stocks by the two tuna Regional Fisheries Management Organisations (tRFMOs) under whose jurisdictions they fall. Individuals caught off the Western Cape, west of the boundary between the tRFMOs at 20°E, are included in assessment and management of the Atlantic Ocean yellowfin tuna stock by the International Commission for the Conservation of Atlantic Tunas (ICCAT), and those caught east of this boundary are assessed and managed as part of the Indian Ocean stock by the Indian Ocean Tuna Commission (IOTC). The boundary between these stocks is based on the confluence of the two oceans in this region and does not incorporate the population structure of species. For sustainable exploitation of fisheries resources, it is important that the definition of management stocks reflects species’ biological population structure; the fine-scale stock structure of yellowfin tuna off South Africa is therefore a research priority which this study aimed to address by means of population genomics analyses. Yellowfin tuna exhibit shallow genetic differentiation over wide geographic areas, and as such traditional population genetic approaches have limited power in resolving fishery significant population structure in the species. Herein, a population genomic approach was employed, specifically, genome-wide analysis of single nucleotide polymorphisms (SNPs) discovered using a next-generation DNA sequencing approach, to confer (i) increased statistical power to detect neutral structuring reflecting population connectivity patterns and (ii) signatures of local adaptation. The mitochondrial Control Region (mtDNA CR) was also sequenced to compare the resolving power of different approaches and to permit coalescent based analyses of the species evolutionary history in the region. Neutral SNP loci revealed significant structure within the dataset (Fst=0.0043; P<0.0001); partitioning of this differentiation within the dataset indicated significant differentiation between yellowfin tuna from the Western Cape and the Gulf of Guinea in the eastern Atlantic Ocean, with no significant differentiation between individuals from the Western Cape and Western Indian Ocean regions. This indicates two population units wherein there is a separation of the Gulf of Guinea from the remaining samples (Indian Ocean including Western Cape) that are largely derived from a single genetic population. This pattern was also supported by assignment tests. Positive outlier SNPs, exhibiting signatures of diversifying selection, suggest that individuals from these regions may be locally adapted, as well as demographically isolated. The mtDNA CR did not reveal any significant genetic structure among samples (Fst=0.0030; P=0.309), demonstrating the increased resolving power provided by population genomics approaches, but revealed signatures of historical demographic fluctuations associated with glacial cycles. Based on the findings of this study, it is suggested that yellowfin tuna caught off the Western Cape of South Africa are migrants from the Indian Ocean population, exhibiting significant genetic differentiation from the Atlantic Ocean Gulf of Guinea individuals, and should thus be included in the assessment and management of the Indian Ocean stock. It is therefore recommended that the boundary between the Atlantic and Indian Ocean yellowfin tuna stocks, under the mandates of ICCAT and the IOTC respectively, should be shifted to approximately 13.35°E to include all individuals caught in South African waters in the Indian Ocean stock.
- Full Text:
- Date Issued: 2017
Post-impoundment population dynamics of non-native common carp Cyprinus Carpio in relation to two large native cyprinids in Lake Gariep, South Africa
- Authors: Winker, Henning
- Date: 2011
- Subjects: Cyprinidae -- South Africa -- Gariep Dam Carp -- South Africa -- Gariep Dam Fish populations -- South Africa -- Gariep Dam Fishes -- Physiology -- South Africa -- Gariep Dam Barbus aeneus -- South Africa -- Gariep Dam Mudfishes -- South Africa -- Gariep Dam Freshwater fishes -- South Africa -- Gariep Dam
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5311 , http://hdl.handle.net/10962/d1005156
- Description: To contribute to the understanding of the invasion biology of common carp Cyprinus carpio in southern Africa, this thesis investigated the life history, relative abundance, long-term population demographics and trophic niche utilisations of non-native common carp C. carpio in relation to two endemic cyprinids, Orange River mudfish Labeo capensis and smallmouth yellowfish Labeobarbus aeneus in South Africa‟s largest impoundment, Lake Gariep. The growth zone deposition rates in astericus otoliths of the three species were validated as biannual for C. carpio and as annual for L. capensis and L. aeneus, which allowed for reliable estimation of lengths-at-age upon which growth, age-at-maturity and mortality rates could be estimated. Cyprinus carpio exhibited fast growth, matured relatively early at two years of age and attained a maximum age of seven years. Labeo capensis grew significantly slower, but attained older ages of up to 12 years. Females showed notably delayed maturation at approximately six years of age. The life history parameter estimates for L. aeneus were similar to those of L. capensis. These species-specific life history characteristics contributed to a substantially higher population growth potential of C. carpio compared to L. capensis and L. aeneus. Delta-lognormal and delta-gamma Generalized Linear Models (GLMs) were used to analyse patterns of relative abundance of L. capensis, L. aeneus and C. carpio. The application of these GLMs was necessary to account for large proportions of zeros and strong skewness in the catch-per-unit-effort (CPUE) from experimental gillnet and fisheries-dependent angler surveys. Confidence intervals around predicted abundance indices were obtained through the development of a generalised parametric bootstrap procedure. The resulting standardised abundance indices were coupled with results from analysis of stable isotope ratios of fish tissues and potential food resources and revealed that C. carpio was mainly confined to soft-bottom habitats, where it predominantly foraged on benthic invertebrates. Labeo capensis was abundant in a wide range of benthic habitats and was consumed basal food resources such as detritus. Labeobarbus aeneus was found to feed mostly on pelagic zooplankton. There were no significant interspecific differences in trophic niche space, suggesting limited resource competition among the three species. Standardised historical and contemporary gillnet CPUE data indicated slow population growth rates of L. capensis and L. aeneus during the first ten years postimpoundment, but showed high biomass levels some four decades after impoundment. These results could be corroborated by stochastic age-structured production model (ASPM) simulations. In contrast to the two endemic species, the gillnet CPUE of C. carpio showed a clear „boom and bust‟ pattern, which, based on ASPM simulations, could be best explained by increased food availability during the first five years postimpoundment, followed by suboptimal conditions thereafter. Together, these results provided evidence that the establishment of the C. carpio population did not prevent the slow but successful long-term establishment of the two large endemic cyprinids. Both endemic fishes revealed specialised feeding within the impoundment.
- Full Text:
- Date Issued: 2011
- Authors: Winker, Henning
- Date: 2011
- Subjects: Cyprinidae -- South Africa -- Gariep Dam Carp -- South Africa -- Gariep Dam Fish populations -- South Africa -- Gariep Dam Fishes -- Physiology -- South Africa -- Gariep Dam Barbus aeneus -- South Africa -- Gariep Dam Mudfishes -- South Africa -- Gariep Dam Freshwater fishes -- South Africa -- Gariep Dam
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5311 , http://hdl.handle.net/10962/d1005156
- Description: To contribute to the understanding of the invasion biology of common carp Cyprinus carpio in southern Africa, this thesis investigated the life history, relative abundance, long-term population demographics and trophic niche utilisations of non-native common carp C. carpio in relation to two endemic cyprinids, Orange River mudfish Labeo capensis and smallmouth yellowfish Labeobarbus aeneus in South Africa‟s largest impoundment, Lake Gariep. The growth zone deposition rates in astericus otoliths of the three species were validated as biannual for C. carpio and as annual for L. capensis and L. aeneus, which allowed for reliable estimation of lengths-at-age upon which growth, age-at-maturity and mortality rates could be estimated. Cyprinus carpio exhibited fast growth, matured relatively early at two years of age and attained a maximum age of seven years. Labeo capensis grew significantly slower, but attained older ages of up to 12 years. Females showed notably delayed maturation at approximately six years of age. The life history parameter estimates for L. aeneus were similar to those of L. capensis. These species-specific life history characteristics contributed to a substantially higher population growth potential of C. carpio compared to L. capensis and L. aeneus. Delta-lognormal and delta-gamma Generalized Linear Models (GLMs) were used to analyse patterns of relative abundance of L. capensis, L. aeneus and C. carpio. The application of these GLMs was necessary to account for large proportions of zeros and strong skewness in the catch-per-unit-effort (CPUE) from experimental gillnet and fisheries-dependent angler surveys. Confidence intervals around predicted abundance indices were obtained through the development of a generalised parametric bootstrap procedure. The resulting standardised abundance indices were coupled with results from analysis of stable isotope ratios of fish tissues and potential food resources and revealed that C. carpio was mainly confined to soft-bottom habitats, where it predominantly foraged on benthic invertebrates. Labeo capensis was abundant in a wide range of benthic habitats and was consumed basal food resources such as detritus. Labeobarbus aeneus was found to feed mostly on pelagic zooplankton. There were no significant interspecific differences in trophic niche space, suggesting limited resource competition among the three species. Standardised historical and contemporary gillnet CPUE data indicated slow population growth rates of L. capensis and L. aeneus during the first ten years postimpoundment, but showed high biomass levels some four decades after impoundment. These results could be corroborated by stochastic age-structured production model (ASPM) simulations. In contrast to the two endemic species, the gillnet CPUE of C. carpio showed a clear „boom and bust‟ pattern, which, based on ASPM simulations, could be best explained by increased food availability during the first five years postimpoundment, followed by suboptimal conditions thereafter. Together, these results provided evidence that the establishment of the C. carpio population did not prevent the slow but successful long-term establishment of the two large endemic cyprinids. Both endemic fishes revealed specialised feeding within the impoundment.
- Full Text:
- Date Issued: 2011
Prioritising native fish populations for conservation using genetics in the Groot Marico catchment, North West Province, South Africa
- Authors: Van der Walt, Kerry-Ann
- Date: 2014
- Subjects: Native fishes Fishery management -- South Africa -- North West Fish populations Fishes -- Conservation -- South Africa -- Western Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/69102 , vital:29390
- Description: The Groot Marico catchment in the North West Province is a National Freshwater Ecosystem Priority Area (NFEPA) because it represents unique landscape features with unique biodiversity that are considered to be of special ecological significance. Three native freshwater species Amphilius uranoscopus, Chiloglanis pretoriae and Barbus motebensis, have high local conservation importance and B. motebensis is endemic to the catchment and is IUCN-listed as vulnerable. The main objective of this study is to contribute towards the effective conservation of these three species in the Groot Marico River system by assessing their genetic structure to determine whether tributary populations of the three species comprise of one genetic population or whether they are divided into genetically distinct subpopulations, in order to prioritise areas for conservation. The central null hypothesis was that there is no genetic differentiation between tributary populations (i.e., panmixia) of B. motebensis, A. uranoscopus and C. pretoriae in the Groot Marico catchment, North West Province. In total, 80 individuals per species were collected, targeting at least 10 individuals per population from a total of eight populations (seven tributaries and the Groot Marico main stem) and across the study area. Samples were collected by electrofishing and specimens were euthanized using an overdose of clove oil. A sample of muscle tissue was removed for genetic evaluation and the remainder of the specimens served as voucher specimens. For the genetic evaluation, mitochondrial (ND2, cyt b) and nuclear (S7) genes were used. Genetic techniques used were DNA extraction, polymerase chain reaction (PCR), purification and sequencing. From the 240 individuals collected, 123 sequences for B. motebensis, 111 sequences for A. uranoscopus and 103 sequences for C. pretoriae were analysed across all three genes. Statistical analysis included looking at cleaned sequences in order to obtain models using MODELTEST (version 3.06). Population structuring and phylogeographic analysis was performed in Arlequin (version 2000), TCS (version 1.2.1) and PAUP*. Results indicated that for B. motebensis the null hypothesis could be rejected as there were two distinct lineages (the Draai and Eastern lineages) that demonstrated significant divergence in both the ND2 and S7 genes, suggesting historical isolation. The low divergence in the mitochondrial cytochrome b gene (0% < D < 0.8%) suggests that this isolation is not very old and is probably not comparable to species level differentiation. The null hypothesis was also rejected for A. uranoscopus as there were also significant levels of differentiation between tributary populations resulting in the identification of two lineages (the Ribbok and Western lineages). However, for C. pretoriae, the null hypothesis could not be rejected as there was no genetic differentiation between tributary populations i.e., one panmictic population. Therefore, due to each species showing different genetic structuring within the tributary populations, more than one priority area for conservation needs to be implemented. These priority areas of conservation where therefore evaluated based on the current conservation status of the species (B. motebensis being vulnerable on the IUCN Red List), the number of Evolutionary Significant Units for each species and the overall genetic diversity of all three species in the Groot Marico catchment. In total, four tributary populations were conservation priorities areas, these were the Draai, Vanstraatens, Ribbok and Kaaloog tributaries. The Draai, Vanstraatens and Kaaloog tributaries were selected as priority areas for B. motebensis (B. motebensis is considered to be the most vulnerable of all three species). The Draai tributary was selected due to the B. motebensis population within the tributary showing isolation from the rest of the tributary populations. In order to conserve B. motebensis from the Southern lineage, the Vanstraatens and Kaaloog tributaries were selected. Reasons for selecting these two specific tributaries within the Southern lineage were that the Vanstraatens tributary had unique alleles (three Evolutionary Significant Units) for B. motebensis and the Kaaloog tributary had high genetic diversity (HD = 0.889, ND2 gene) when compared to the other tributary populations. The Ribbok and Vanstraatens tributaries were selected as priority areas for the conservation of A. uranoscopus. The Ribbok tributary was selected as it showed isolation from the rest of the tributary populations, as seen with the Draai tributary (B. motebensis) and the Vanstraatens tributary was selected to represent the Western lineage as it had the highest diversity for both genes (ND2 and S7). The Ribbok tributary has the highest prioritisation when compared to the Vanstraatens tributary. Chiloglanis pretoriae occurs within the Draai, Vanstraatens, Ribbok and Kaaloog tributaries, therefore by prioritising these tributaries for conservation, C. pretoriae will in turn be conserved.
- Full Text:
- Date Issued: 2014
- Authors: Van der Walt, Kerry-Ann
- Date: 2014
- Subjects: Native fishes Fishery management -- South Africa -- North West Fish populations Fishes -- Conservation -- South Africa -- Western Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/69102 , vital:29390
- Description: The Groot Marico catchment in the North West Province is a National Freshwater Ecosystem Priority Area (NFEPA) because it represents unique landscape features with unique biodiversity that are considered to be of special ecological significance. Three native freshwater species Amphilius uranoscopus, Chiloglanis pretoriae and Barbus motebensis, have high local conservation importance and B. motebensis is endemic to the catchment and is IUCN-listed as vulnerable. The main objective of this study is to contribute towards the effective conservation of these three species in the Groot Marico River system by assessing their genetic structure to determine whether tributary populations of the three species comprise of one genetic population or whether they are divided into genetically distinct subpopulations, in order to prioritise areas for conservation. The central null hypothesis was that there is no genetic differentiation between tributary populations (i.e., panmixia) of B. motebensis, A. uranoscopus and C. pretoriae in the Groot Marico catchment, North West Province. In total, 80 individuals per species were collected, targeting at least 10 individuals per population from a total of eight populations (seven tributaries and the Groot Marico main stem) and across the study area. Samples were collected by electrofishing and specimens were euthanized using an overdose of clove oil. A sample of muscle tissue was removed for genetic evaluation and the remainder of the specimens served as voucher specimens. For the genetic evaluation, mitochondrial (ND2, cyt b) and nuclear (S7) genes were used. Genetic techniques used were DNA extraction, polymerase chain reaction (PCR), purification and sequencing. From the 240 individuals collected, 123 sequences for B. motebensis, 111 sequences for A. uranoscopus and 103 sequences for C. pretoriae were analysed across all three genes. Statistical analysis included looking at cleaned sequences in order to obtain models using MODELTEST (version 3.06). Population structuring and phylogeographic analysis was performed in Arlequin (version 2000), TCS (version 1.2.1) and PAUP*. Results indicated that for B. motebensis the null hypothesis could be rejected as there were two distinct lineages (the Draai and Eastern lineages) that demonstrated significant divergence in both the ND2 and S7 genes, suggesting historical isolation. The low divergence in the mitochondrial cytochrome b gene (0% < D < 0.8%) suggests that this isolation is not very old and is probably not comparable to species level differentiation. The null hypothesis was also rejected for A. uranoscopus as there were also significant levels of differentiation between tributary populations resulting in the identification of two lineages (the Ribbok and Western lineages). However, for C. pretoriae, the null hypothesis could not be rejected as there was no genetic differentiation between tributary populations i.e., one panmictic population. Therefore, due to each species showing different genetic structuring within the tributary populations, more than one priority area for conservation needs to be implemented. These priority areas of conservation where therefore evaluated based on the current conservation status of the species (B. motebensis being vulnerable on the IUCN Red List), the number of Evolutionary Significant Units for each species and the overall genetic diversity of all three species in the Groot Marico catchment. In total, four tributary populations were conservation priorities areas, these were the Draai, Vanstraatens, Ribbok and Kaaloog tributaries. The Draai, Vanstraatens and Kaaloog tributaries were selected as priority areas for B. motebensis (B. motebensis is considered to be the most vulnerable of all three species). The Draai tributary was selected due to the B. motebensis population within the tributary showing isolation from the rest of the tributary populations. In order to conserve B. motebensis from the Southern lineage, the Vanstraatens and Kaaloog tributaries were selected. Reasons for selecting these two specific tributaries within the Southern lineage were that the Vanstraatens tributary had unique alleles (three Evolutionary Significant Units) for B. motebensis and the Kaaloog tributary had high genetic diversity (HD = 0.889, ND2 gene) when compared to the other tributary populations. The Ribbok and Vanstraatens tributaries were selected as priority areas for the conservation of A. uranoscopus. The Ribbok tributary was selected as it showed isolation from the rest of the tributary populations, as seen with the Draai tributary (B. motebensis) and the Vanstraatens tributary was selected to represent the Western lineage as it had the highest diversity for both genes (ND2 and S7). The Ribbok tributary has the highest prioritisation when compared to the Vanstraatens tributary. Chiloglanis pretoriae occurs within the Draai, Vanstraatens, Ribbok and Kaaloog tributaries, therefore by prioritising these tributaries for conservation, C. pretoriae will in turn be conserved.
- Full Text:
- Date Issued: 2014
Progress in implementing the ecosystem approach to fisheries in South Africa in principle and in practice
- Duna, Elethu Zamandlane Lona
- Authors: Duna, Elethu Zamandlane Lona
- Date: 2017
- Subjects: Fisheries -- Environmental aspects -- South Africa , Sustainable fisheries -- South Africa , Fishery management -- South Africa , South African Sustainable Seafood Initiative
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/44879 , vital:25449
- Description: Over the last century, the population of the world has more than doubled, resulting in an increase in seafood consumption (FAO 2010), and placing strain on fisheries wild stocks, their habitats, and the coastal communities that rely on them for food and survival. The ecosystem approach to fisheries (EAF) differs from other management approaches by combining all aspects of ecosystem management, and strives to conserve ecosystem structure, maintain diversity, productivity, and integrity, and to meet human food and economic needs. This study aims to assess how South Africa is progressing in implementing EAF in principle and in practice, to identify challenges, and suggest solutions, where appropriate. The law sets precedence on governance. An assessment of the Marine Living Resources Act, (MLRA) and the South African Policy for Small-scale Fisheries (SSFP) revealed that, although these instruments recognise and contain elements of EAF, this management approach has not been adequately implemented. In practice, the status of implementation of EAF was assessed through the Southern African Sustainable Seafood Initiative (SASSI) and the Ecological Risk Assessments (ERA). The scores of 65 assessments, conducted in 2013 and 2014, were obtained from SASSI. Of the 65 species assessed; 18.4% were listed as Green, 50.8% were listed as Orange and 30.8% were listed as Red. Two methods were used to analyse the data; non-metric multidimensional scaling (NMDS), and cluster analysis in the statistical program R. Analysis of the SASSI assessments indicates that there has been progress in implementing EAF since the World Summit on Sustainable Development in 2002. The high number of Orange and Red listed species however, indicate that major sustainability issues still exist. Species in commercially important fisheries enjoy the bulk of research and management attention compared to other species, including bycatch species, as reflected by a high proportion of Green-rated commercially important species. Based on these results, four fisheries were chosen for further indepth analysis using additional information found in ecological risk assessments: offshore demersal trawl, inshore demersal trawl, West Coast rock lobster fishery and the line fishery. The documents and published literature of the Department of Agriculture, Forestry and Fisheries Internal Scientific Working Groups provided further information. A Wilcoxon signed rank test conducted in the programme R on the results of the ERAs showed that there was a decline in implementation of EAF and reinforced the earlier conclusion that large commercial fisheries, offshore and inshore demersal trawl, were progressing in implementing EAF faster than West Coast rock lobster and line fisheries, which are examples of smaller-scale fisheries that are more accessible to many resource users. Both progress and challenges appeared to be largely influenced by several common factors, which include the presence or absence of positive incentives, co-management, management plans, access, compliance, economic importance, capacity, and the interests of rights holders and other stakeholders.
- Full Text:
- Date Issued: 2017
- Authors: Duna, Elethu Zamandlane Lona
- Date: 2017
- Subjects: Fisheries -- Environmental aspects -- South Africa , Sustainable fisheries -- South Africa , Fishery management -- South Africa , South African Sustainable Seafood Initiative
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/44879 , vital:25449
- Description: Over the last century, the population of the world has more than doubled, resulting in an increase in seafood consumption (FAO 2010), and placing strain on fisheries wild stocks, their habitats, and the coastal communities that rely on them for food and survival. The ecosystem approach to fisheries (EAF) differs from other management approaches by combining all aspects of ecosystem management, and strives to conserve ecosystem structure, maintain diversity, productivity, and integrity, and to meet human food and economic needs. This study aims to assess how South Africa is progressing in implementing EAF in principle and in practice, to identify challenges, and suggest solutions, where appropriate. The law sets precedence on governance. An assessment of the Marine Living Resources Act, (MLRA) and the South African Policy for Small-scale Fisheries (SSFP) revealed that, although these instruments recognise and contain elements of EAF, this management approach has not been adequately implemented. In practice, the status of implementation of EAF was assessed through the Southern African Sustainable Seafood Initiative (SASSI) and the Ecological Risk Assessments (ERA). The scores of 65 assessments, conducted in 2013 and 2014, were obtained from SASSI. Of the 65 species assessed; 18.4% were listed as Green, 50.8% were listed as Orange and 30.8% were listed as Red. Two methods were used to analyse the data; non-metric multidimensional scaling (NMDS), and cluster analysis in the statistical program R. Analysis of the SASSI assessments indicates that there has been progress in implementing EAF since the World Summit on Sustainable Development in 2002. The high number of Orange and Red listed species however, indicate that major sustainability issues still exist. Species in commercially important fisheries enjoy the bulk of research and management attention compared to other species, including bycatch species, as reflected by a high proportion of Green-rated commercially important species. Based on these results, four fisheries were chosen for further indepth analysis using additional information found in ecological risk assessments: offshore demersal trawl, inshore demersal trawl, West Coast rock lobster fishery and the line fishery. The documents and published literature of the Department of Agriculture, Forestry and Fisheries Internal Scientific Working Groups provided further information. A Wilcoxon signed rank test conducted in the programme R on the results of the ERAs showed that there was a decline in implementation of EAF and reinforced the earlier conclusion that large commercial fisheries, offshore and inshore demersal trawl, were progressing in implementing EAF faster than West Coast rock lobster and line fisheries, which are examples of smaller-scale fisheries that are more accessible to many resource users. Both progress and challenges appeared to be largely influenced by several common factors, which include the presence or absence of positive incentives, co-management, management plans, access, compliance, economic importance, capacity, and the interests of rights holders and other stakeholders.
- Full Text:
- Date Issued: 2017
Puerulus and early juvenile recruitment of the rock lobster jasus lalandii in relation to the environment at Lüderitz Bay, Namibia
- Authors: Keulder, Felicia Juanita
- Date: 2005
- Subjects: Jasus lalandii , Lobster fisheries -- Namibia , Lobster culture -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5315 , http://hdl.handle.net/10962/d1005160 , Jasus lalandii , Lobster fisheries -- Namibia , Lobster culture -- Namibia
- Description: A global decline in the lobster fishery has necessitated the growout of wild-caught postlarvae (pueruli) on farms to meet the worlds lobster demand. A limited knowledge on puerulus settlement in the West Coast rock lobster (Jasus lalandii) constitutes a major barrier for J. lalandii culture development in Southern Africa. As an extension of an existing long-term puerulus monitoring program of the Ministry of Fisheries and Marine Resources of Namibia, the present study monitored puerulus recruitment (supply), puerulus condition and juvenile growth of J. lalandii and their relationship with environmental variables on an oyster farm at Lüderitz Bay, Namibia. Implications for lobster aquaculture and fisheries management are discussed. Oyster bags, crates and collectors were sampled daily, weekly and bimonthly, for pueruli and juveniles, respectively, between August 2001 and July 2003 to establish spatialtemporal patterns in their distribution. Animals were transported to the laboratory for morphometric analyses where they were staged as puerulus (Pt = transparent; Pp = pigmented) and juvenile lobsters. The carapace lengths (0.1mm CL) and wet weights (0.01gram) of animals were recorded. Carapace length frequencies were subjected to Modal Progression analysis to identify early juvenile cohorts and calculate their growths. The weight-length ratios calculated and percentage fat content were used as indices of nutritional condition. Seasonal peaks in puerulus and juvenile abundance were estimated using Periodic Regression analysis. The relationships of puerulus and juvenile abundance with respect to sea surface temperature (SST), wind speed-direction, moon phase, swell and tidal range were established using time lag analysis (ADL). Transparent pueruli were randomly distributed on oyster bags and crates, and also between collector sites, suggesting that they have no particular settlement preference for certain areas on these structures (p>0.05; n=150). Pigmented puerulus (p<0.05; n=566) and juveniles (p<0.05; n=3528) preferred structurally complex structures that provided better shelter such as crates, which were more sheltered from sea swells, compared to oyster bags. Among oyster rafts, pigmented puerulus and juveniles preferred occupying the sheltered and centred raft areas, which provided better protection from wave action, compared to exposed raft areas, which were exposed to the incoming swell. Puerulus and juvenile lobster appeared to recolonise adjacent bags and crates, and possibly migrate to the substrate and off the farm due to the disturbance of the habitat during harvesting. The booth crevice collector was more efficient in collecting puerulus possibly due to the high structurally complex habitat and the better shelter they provided compared to the hogshair collector. The occupation of structurally complex habitats by early benthic stages may be related to morphological changes associated with metamorphosis. Puerulus settlement peaked during early spring (August-September) and was related to low sea surface temperatures (12.3°C), strong south winds, and moderate swells in the week preceding settlement. These conditions are synonymous with the “spring upwelling” season of the Lüderitz upwelling cell in the central Benguela current region. Puerulus nutritional condition peaked during this period possibly due to high levels of planktonic food (due to high nutrients from upwelling) that was available to the late stage phyllosoma larvae further offshore. A “good” puerulus settlement year during 2000 was associated with lower than average SST (11.6°C) and strong south winds and was followed by “poor” puerulus settlement years during 2001 and 2002 when higher than average SST were experienced with below average wind speeds experienced during 2001 only. Puerulus of J. lalandii recruited in high numbers into Lüderitz Bay during the new moon, full moon and last quarter moon phases by making use of the increased tides during these phases of the lunar cycle. Peak juvenile abundance during early summer (November-December) lagged by 8 weeks was significantly correlated with peak puerulus abundance. Puerulus size was similar (8.5–9.7mm CL) over the study period. Juvenile cohorts, 9.9-20.6mm CL in size recruited in 2 distinct waves in August 2001-June 2002 and July 2002-February 2003. The 2001/2002 recruits had higher monthly growth increments and better nutritional condition compared to 2002/2003 recruits. Peak frequencies of 2nd moult juveniles (9.9- 10.8mm CL) occurred in September of both recruitment events with nutritional condition being poorest during the 2002/2003 event. The nutritional condition of the settling puerulus did not appear to be related to the subsequent growth of juvenile lobster. These preliminary results suggest that pueruli recruit once a year mainly during late winter/ early spring under conditions typical of coastal upwelling in the Benguela current near Lüderitz. It appears that puerulus settlement is driven by favourable shoreward currents, which help in transporting puerulus to their settlement grounds. Puerulus supply is highly variable between years, which appears to be consistent with a highly variable Benguela environment. The oyster farm supported a substantial standing stock averaging 123 800 lobster per day (range: 22 600-325 300 lobster per day) of which 26 600 were puerulus and 97 200 were juveniles, that may have been harvested once off on any given day during the sample period. Monthly harvesting of the total lobster standing stock during the one and a half year sampling period was just over 2 million lobsters (505 700 pueruli and 1.85 million juveniles) and would potentially have been sufficient seed for a 200 ton lobster production in puerulus lobster growout facilities. In the light of high inter-annual variation in puerulus settlement observed at Lüderitz, the seed supply at the Lüderitz oyster farm is clearly limited and therefore it is prudent that other sites of high puerulus settlement is established before large commercial scale lobster growout can commence. The migration of lobster off the farm suggested that these lobsters potentially recruit to the fishery and therefore harvesting the entire standing stock on the farm may have adverse negative effects on the wild fishery. A policy decision will be required as to whether more efficient harvesting of lobster from the farm should be allowed. If puerulus removal in J. lalandii for aquaculture is allowed in the near future, it should be conducted on an experimental scale or small commercial scale until the potential effects on recruitment into the fishery are clearer.
- Full Text:
- Date Issued: 2005
- Authors: Keulder, Felicia Juanita
- Date: 2005
- Subjects: Jasus lalandii , Lobster fisheries -- Namibia , Lobster culture -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5315 , http://hdl.handle.net/10962/d1005160 , Jasus lalandii , Lobster fisheries -- Namibia , Lobster culture -- Namibia
- Description: A global decline in the lobster fishery has necessitated the growout of wild-caught postlarvae (pueruli) on farms to meet the worlds lobster demand. A limited knowledge on puerulus settlement in the West Coast rock lobster (Jasus lalandii) constitutes a major barrier for J. lalandii culture development in Southern Africa. As an extension of an existing long-term puerulus monitoring program of the Ministry of Fisheries and Marine Resources of Namibia, the present study monitored puerulus recruitment (supply), puerulus condition and juvenile growth of J. lalandii and their relationship with environmental variables on an oyster farm at Lüderitz Bay, Namibia. Implications for lobster aquaculture and fisheries management are discussed. Oyster bags, crates and collectors were sampled daily, weekly and bimonthly, for pueruli and juveniles, respectively, between August 2001 and July 2003 to establish spatialtemporal patterns in their distribution. Animals were transported to the laboratory for morphometric analyses where they were staged as puerulus (Pt = transparent; Pp = pigmented) and juvenile lobsters. The carapace lengths (0.1mm CL) and wet weights (0.01gram) of animals were recorded. Carapace length frequencies were subjected to Modal Progression analysis to identify early juvenile cohorts and calculate their growths. The weight-length ratios calculated and percentage fat content were used as indices of nutritional condition. Seasonal peaks in puerulus and juvenile abundance were estimated using Periodic Regression analysis. The relationships of puerulus and juvenile abundance with respect to sea surface temperature (SST), wind speed-direction, moon phase, swell and tidal range were established using time lag analysis (ADL). Transparent pueruli were randomly distributed on oyster bags and crates, and also between collector sites, suggesting that they have no particular settlement preference for certain areas on these structures (p>0.05; n=150). Pigmented puerulus (p<0.05; n=566) and juveniles (p<0.05; n=3528) preferred structurally complex structures that provided better shelter such as crates, which were more sheltered from sea swells, compared to oyster bags. Among oyster rafts, pigmented puerulus and juveniles preferred occupying the sheltered and centred raft areas, which provided better protection from wave action, compared to exposed raft areas, which were exposed to the incoming swell. Puerulus and juvenile lobster appeared to recolonise adjacent bags and crates, and possibly migrate to the substrate and off the farm due to the disturbance of the habitat during harvesting. The booth crevice collector was more efficient in collecting puerulus possibly due to the high structurally complex habitat and the better shelter they provided compared to the hogshair collector. The occupation of structurally complex habitats by early benthic stages may be related to morphological changes associated with metamorphosis. Puerulus settlement peaked during early spring (August-September) and was related to low sea surface temperatures (12.3°C), strong south winds, and moderate swells in the week preceding settlement. These conditions are synonymous with the “spring upwelling” season of the Lüderitz upwelling cell in the central Benguela current region. Puerulus nutritional condition peaked during this period possibly due to high levels of planktonic food (due to high nutrients from upwelling) that was available to the late stage phyllosoma larvae further offshore. A “good” puerulus settlement year during 2000 was associated with lower than average SST (11.6°C) and strong south winds and was followed by “poor” puerulus settlement years during 2001 and 2002 when higher than average SST were experienced with below average wind speeds experienced during 2001 only. Puerulus of J. lalandii recruited in high numbers into Lüderitz Bay during the new moon, full moon and last quarter moon phases by making use of the increased tides during these phases of the lunar cycle. Peak juvenile abundance during early summer (November-December) lagged by 8 weeks was significantly correlated with peak puerulus abundance. Puerulus size was similar (8.5–9.7mm CL) over the study period. Juvenile cohorts, 9.9-20.6mm CL in size recruited in 2 distinct waves in August 2001-June 2002 and July 2002-February 2003. The 2001/2002 recruits had higher monthly growth increments and better nutritional condition compared to 2002/2003 recruits. Peak frequencies of 2nd moult juveniles (9.9- 10.8mm CL) occurred in September of both recruitment events with nutritional condition being poorest during the 2002/2003 event. The nutritional condition of the settling puerulus did not appear to be related to the subsequent growth of juvenile lobster. These preliminary results suggest that pueruli recruit once a year mainly during late winter/ early spring under conditions typical of coastal upwelling in the Benguela current near Lüderitz. It appears that puerulus settlement is driven by favourable shoreward currents, which help in transporting puerulus to their settlement grounds. Puerulus supply is highly variable between years, which appears to be consistent with a highly variable Benguela environment. The oyster farm supported a substantial standing stock averaging 123 800 lobster per day (range: 22 600-325 300 lobster per day) of which 26 600 were puerulus and 97 200 were juveniles, that may have been harvested once off on any given day during the sample period. Monthly harvesting of the total lobster standing stock during the one and a half year sampling period was just over 2 million lobsters (505 700 pueruli and 1.85 million juveniles) and would potentially have been sufficient seed for a 200 ton lobster production in puerulus lobster growout facilities. In the light of high inter-annual variation in puerulus settlement observed at Lüderitz, the seed supply at the Lüderitz oyster farm is clearly limited and therefore it is prudent that other sites of high puerulus settlement is established before large commercial scale lobster growout can commence. The migration of lobster off the farm suggested that these lobsters potentially recruit to the fishery and therefore harvesting the entire standing stock on the farm may have adverse negative effects on the wild fishery. A policy decision will be required as to whether more efficient harvesting of lobster from the farm should be allowed. If puerulus removal in J. lalandii for aquaculture is allowed in the near future, it should be conducted on an experimental scale or small commercial scale until the potential effects on recruitment into the fishery are clearer.
- Full Text:
- Date Issued: 2005
Quantifying feed intake and feeding intensity using two experimental conditions and the effect of different feeding strategies on the production parameters of farmed South African abalone, haliotis midae
- Authors: Wortley, Ross Michael
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/${Handle} , vital:71932
- Description: As abalone are slow-growing animals there is a high investment of capital, running costs and labour in commercial abalone farming. Revenue needs to be maximised by achieving fast growth rates. A foremost driver of abalone growth is feed intake and feeding intensity of the abalone as well as the feeding regimen a farm utilises. While feed intake is well-documented in H. midae, there is a paucity of information regarding this aspect in abalone above 70 g and the relationship between feeding intensity, feed conversion rate (FCR) and daily growth rate needs to be documented. Similarly, there are a limited number of studies dealing with the effects of different pellet types of the same formulation, that differ only in shape and size, on feed intake and production in H. midae. This study made use of both a controlled laboratory experiment and commercial-scale farm experiment with the aim of testing whether feed intake information produced under laboratory conditions can provide good estimates of feed intake under farming conditions, which can further be implemented into feeding strategies on abalone farms. This study quantified daily feed intake (F) in 10 – 20 g, 100 – 110 g and 150 – 160 g abalone weight classes using two different pellet types and determined the relationship between the duration of feed availability and feed intake under laboratory conditions. The effect of three different pellet type strategies (fed daily: a leaf-only strategy = L d-1, a short-pellet only strategy = SP d-1, and a strategy that used both = B d-1) on abalone production parameters under farming conditions such as growth rate, feed conversion ratio (FCR), feeding intensity (FI) and weight variation of 30 – 40 g H. midae was also investigated. A commercial-scale farm study was designed to test the effect of four commercially relevant feeding regimens (three size-specific regimens and one commercially practiced feeding method) on the growth, FCR, feeding intensity and weight variation of these three abalone weight classes while taking into account an economic model to assess the profitability of each feeding regimen. Daily feed intake as a percentage of body mass (% BM d-1) was a function of abalone weight class between the 10 – 20 g and two larger weight classes 100 – 110 g and 150 – 160 g p < 0.0001), however feed intake was not different between the 100 – 110 g and 150 – 160 g weight classes. Pellet type did not affect feed intake in all abalone weight classes (p = 0.15). Feed intake (F) was positively linearly correlated with duration of feed availability (h) in the 10 – 20 g weight class (r2 = 0.76, p <0.00001) and logarithmically correlated in the 100 – 110 g (r2 = 0.25, p < 0.02) and 150 – 160 g (r2 = 0.52, p < 0.0001) weight classes (10 – 20 g abalone-1: 3 F (% BM) = 0.02(h) + 0.1976, 100 – 110 g abalone-1: F (% BM) = log10(h)*0.17 + 0.17, 150 – 160 g abalone-1: F (% BM) = log10(h)*0.36 + 0.07). There was no significant difference in monthly average abalone weight, daily growth rate (G), FCR and feeding intensity between each pellet type strategy (G: p = 0.60, FCR: p = 0.62, FI: p = 0.54 ). However, abalone grew well over the 112-day growth period with average abalone weight increasing significantly between each monthly sample time (pooled pellet type strategy: Huynh-Feldt correction; p < 0.00001). Furthermore, abalone fed the leaf-only pellet type strategy (L d-1) fell into higher weight classes after a 112-day growth period (Z test: 50 – 70 g: 72%) which was 16.1 % higher compared to the SP d-1 and B d-1 strategies. Daily growth rate (r2 = 0.34, p < 0.01) and FCR (r2 = 0.42, p < 0.004) was negatively correlated and FCR was positively correlated with daily feeding intensity, respectively (G = - 2.59 (FI) + 1.526, FCR = 8.8082 (FI) – 2.7108). Feeding regimen affected the production parameters of three abalone weight classes. The method practiced on the farm resulted in the best growth in the 10 – 20 g abalone weight class. The farm feeding method resulted in slower yet more efficient growth rates (lowest FCR values) in the abalone weight classes, 100 – 110 g and 150 – 160 g abalone- 1. However, size-specific feeding regimens resulted in the fastest growth rates but resulted in higher FCR values (less efficient). The relationship between feeding intensity, daily growth rate and FCR all showed that an increase in feeding intensity results in increased daily growth rates and FCR values. The economic model suggests that the higher FCR values associated with size-specific regimens, which have higher associated costs to producing abalone, were greatly outweighed by the growth attained by the abalone in the 100 – 110 g and 150 – 160 g weight classes. The size-specific regimens generated a higher potential monetary value of abalone after a 112-day period, which would consequently result in higher income for abalone farms. For abalone ranging from 100 – 110 and 150 – 160 grams, the economic model suggested that in a quarterly grading schedule (112 days) that abalone be fed the size specific daily rations, which is a function of body mass, at 0.35 % BM d-1 and 0.352 % BM d-1, respectively. The two experimental conditions used in this study produced feed intake and production parameter information that is beneficial to South African abalone farmers. The small-scale laboratory study produced information on feed intake that can be used as reference values as to what abalone in these weight classes can consume on a daily basis. The laboratory study can provide estimates of feed intake under farming conditions but should only be used as minimum 4 values when determining size-specific feeding regimens. To maximise abalone growth, farmers should utilise size-specific feeding regimens for abalone above 30 g. Daily growth rate and FCR can be predicted as a function of the abalone’s feeding intensity. Further studies are needed to determine the effects of abalone weight class on production parameters when testing different pellet types as well as an exploration into behavioural studies focusing on diet preferences. Additionally, future studies need to take into consideration abalone above the weight of 100 g with additional focus of research on behavioural, genetic and environmental aspects on abalone feed intake. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-29
- Authors: Wortley, Ross Michael
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/${Handle} , vital:71932
- Description: As abalone are slow-growing animals there is a high investment of capital, running costs and labour in commercial abalone farming. Revenue needs to be maximised by achieving fast growth rates. A foremost driver of abalone growth is feed intake and feeding intensity of the abalone as well as the feeding regimen a farm utilises. While feed intake is well-documented in H. midae, there is a paucity of information regarding this aspect in abalone above 70 g and the relationship between feeding intensity, feed conversion rate (FCR) and daily growth rate needs to be documented. Similarly, there are a limited number of studies dealing with the effects of different pellet types of the same formulation, that differ only in shape and size, on feed intake and production in H. midae. This study made use of both a controlled laboratory experiment and commercial-scale farm experiment with the aim of testing whether feed intake information produced under laboratory conditions can provide good estimates of feed intake under farming conditions, which can further be implemented into feeding strategies on abalone farms. This study quantified daily feed intake (F) in 10 – 20 g, 100 – 110 g and 150 – 160 g abalone weight classes using two different pellet types and determined the relationship between the duration of feed availability and feed intake under laboratory conditions. The effect of three different pellet type strategies (fed daily: a leaf-only strategy = L d-1, a short-pellet only strategy = SP d-1, and a strategy that used both = B d-1) on abalone production parameters under farming conditions such as growth rate, feed conversion ratio (FCR), feeding intensity (FI) and weight variation of 30 – 40 g H. midae was also investigated. A commercial-scale farm study was designed to test the effect of four commercially relevant feeding regimens (three size-specific regimens and one commercially practiced feeding method) on the growth, FCR, feeding intensity and weight variation of these three abalone weight classes while taking into account an economic model to assess the profitability of each feeding regimen. Daily feed intake as a percentage of body mass (% BM d-1) was a function of abalone weight class between the 10 – 20 g and two larger weight classes 100 – 110 g and 150 – 160 g p < 0.0001), however feed intake was not different between the 100 – 110 g and 150 – 160 g weight classes. Pellet type did not affect feed intake in all abalone weight classes (p = 0.15). Feed intake (F) was positively linearly correlated with duration of feed availability (h) in the 10 – 20 g weight class (r2 = 0.76, p <0.00001) and logarithmically correlated in the 100 – 110 g (r2 = 0.25, p < 0.02) and 150 – 160 g (r2 = 0.52, p < 0.0001) weight classes (10 – 20 g abalone-1: 3 F (% BM) = 0.02(h) + 0.1976, 100 – 110 g abalone-1: F (% BM) = log10(h)*0.17 + 0.17, 150 – 160 g abalone-1: F (% BM) = log10(h)*0.36 + 0.07). There was no significant difference in monthly average abalone weight, daily growth rate (G), FCR and feeding intensity between each pellet type strategy (G: p = 0.60, FCR: p = 0.62, FI: p = 0.54 ). However, abalone grew well over the 112-day growth period with average abalone weight increasing significantly between each monthly sample time (pooled pellet type strategy: Huynh-Feldt correction; p < 0.00001). Furthermore, abalone fed the leaf-only pellet type strategy (L d-1) fell into higher weight classes after a 112-day growth period (Z test: 50 – 70 g: 72%) which was 16.1 % higher compared to the SP d-1 and B d-1 strategies. Daily growth rate (r2 = 0.34, p < 0.01) and FCR (r2 = 0.42, p < 0.004) was negatively correlated and FCR was positively correlated with daily feeding intensity, respectively (G = - 2.59 (FI) + 1.526, FCR = 8.8082 (FI) – 2.7108). Feeding regimen affected the production parameters of three abalone weight classes. The method practiced on the farm resulted in the best growth in the 10 – 20 g abalone weight class. The farm feeding method resulted in slower yet more efficient growth rates (lowest FCR values) in the abalone weight classes, 100 – 110 g and 150 – 160 g abalone- 1. However, size-specific feeding regimens resulted in the fastest growth rates but resulted in higher FCR values (less efficient). The relationship between feeding intensity, daily growth rate and FCR all showed that an increase in feeding intensity results in increased daily growth rates and FCR values. The economic model suggests that the higher FCR values associated with size-specific regimens, which have higher associated costs to producing abalone, were greatly outweighed by the growth attained by the abalone in the 100 – 110 g and 150 – 160 g weight classes. The size-specific regimens generated a higher potential monetary value of abalone after a 112-day period, which would consequently result in higher income for abalone farms. For abalone ranging from 100 – 110 and 150 – 160 grams, the economic model suggested that in a quarterly grading schedule (112 days) that abalone be fed the size specific daily rations, which is a function of body mass, at 0.35 % BM d-1 and 0.352 % BM d-1, respectively. The two experimental conditions used in this study produced feed intake and production parameter information that is beneficial to South African abalone farmers. The small-scale laboratory study produced information on feed intake that can be used as reference values as to what abalone in these weight classes can consume on a daily basis. The laboratory study can provide estimates of feed intake under farming conditions but should only be used as minimum 4 values when determining size-specific feeding regimens. To maximise abalone growth, farmers should utilise size-specific feeding regimens for abalone above 30 g. Daily growth rate and FCR can be predicted as a function of the abalone’s feeding intensity. Further studies are needed to determine the effects of abalone weight class on production parameters when testing different pellet types as well as an exploration into behavioural studies focusing on diet preferences. Additionally, future studies need to take into consideration abalone above the weight of 100 g with additional focus of research on behavioural, genetic and environmental aspects on abalone feed intake. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-29
Quantifying the ecological and socioeconomic implications of a recovery/collapse of South Africa’s West Coast rock lobster fishery
- Authors: Eggers, Jessica Marguerite
- Date: 2021-10
- Subjects: Jasus lalandii South Africa , Lobster fisheries South Africa , Lobster fisheries Catch effort South Africa , Fishery management South Africa , Small-scale fisheries South Africa , Economics Sociological aspects , Value chain analysis
- Language: English
- Type: Masters theses , text
- Identifier: http://hdl.handle.net/10962/188854 , vital:44792
- Description: The West Coast rock lobster (WCRL) Jasus lalandii fishery is South Africa’s third most valuable fishery, but the stock is currently at less than 2% of its pristine biomass. Scientists are warning that if no measures are taken, the WCRL could face commercial extinction. The necessary reductions in the global Total allowable Catch (TAC) seen in past years have had large economic implications for the WCRL value chain, but research into the socio-economic aspects of this fishery is limited. This study, therefore, aims to establish an overview of the economic revenue over the seasons 2016/17 – 2018/19 by exploring changes and trends in the net seasonal income (NSI) for the fishery, sectors within the fishery and different stakeholders. It also investigates the prospects for the sectors and different actors in this fishery over the seasons 2019/2020 - 2030/31 through analysis of the net present value (NPV) under three proposed global TAC management scenarios (global TAC of 640 tonnes, 1084 tonnes and 1280 tonnes). Data concerning costs and incomes as well as dynamics, mechanisms and concerns surrounding the fishery were collected from stakeholders in the different sectors through interviews and surveys. Further, official records from DEFF (catches, actors, vessels and quotas) and projections made by the Marine Resource Assessment (MARAM) team at the University of Cape Town (rates of recovery of the resource and future catches under the different TAC scenarios) were obtained and analysed. Cost and income data were summarised and models characterising the economic flows within the fishery were created. Calculations regarding the NSI and NPV were made using Monte Carlo simulations to account for the uncertainty surrounding many of the input variables. Results show that while the fishery as a whole made economic profits for the three seasons, the decreasing quotas in 2018/19 had a disproportionately negative impact on some of the representative individuals examined within the different sectors. The projections indicate that while each of the sectors as a whole would continue to make profits largely proportional to their allocation under the different TAC scenarios, many vessel owners in the fishery are likely to face economic losses or very marginal gains under the lower quota options, while the NPV for quota holders who outsource the catching of their quota are likely to be proportionally less affected by the changes in global TAC. This dynamic is important to consider for the future of this fishery. If the resource is to recover, and fishing activity is to continue equitably under the decreased quotas that the recovery of the biomass necessitates, the socio-economic context and the dynamics within which the fishers operate must be considered and studied more extensively and socio-economic consequences of a lower global TAC mitigated while improving the ecological status of the resource. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10
- Authors: Eggers, Jessica Marguerite
- Date: 2021-10
- Subjects: Jasus lalandii South Africa , Lobster fisheries South Africa , Lobster fisheries Catch effort South Africa , Fishery management South Africa , Small-scale fisheries South Africa , Economics Sociological aspects , Value chain analysis
- Language: English
- Type: Masters theses , text
- Identifier: http://hdl.handle.net/10962/188854 , vital:44792
- Description: The West Coast rock lobster (WCRL) Jasus lalandii fishery is South Africa’s third most valuable fishery, but the stock is currently at less than 2% of its pristine biomass. Scientists are warning that if no measures are taken, the WCRL could face commercial extinction. The necessary reductions in the global Total allowable Catch (TAC) seen in past years have had large economic implications for the WCRL value chain, but research into the socio-economic aspects of this fishery is limited. This study, therefore, aims to establish an overview of the economic revenue over the seasons 2016/17 – 2018/19 by exploring changes and trends in the net seasonal income (NSI) for the fishery, sectors within the fishery and different stakeholders. It also investigates the prospects for the sectors and different actors in this fishery over the seasons 2019/2020 - 2030/31 through analysis of the net present value (NPV) under three proposed global TAC management scenarios (global TAC of 640 tonnes, 1084 tonnes and 1280 tonnes). Data concerning costs and incomes as well as dynamics, mechanisms and concerns surrounding the fishery were collected from stakeholders in the different sectors through interviews and surveys. Further, official records from DEFF (catches, actors, vessels and quotas) and projections made by the Marine Resource Assessment (MARAM) team at the University of Cape Town (rates of recovery of the resource and future catches under the different TAC scenarios) were obtained and analysed. Cost and income data were summarised and models characterising the economic flows within the fishery were created. Calculations regarding the NSI and NPV were made using Monte Carlo simulations to account for the uncertainty surrounding many of the input variables. Results show that while the fishery as a whole made economic profits for the three seasons, the decreasing quotas in 2018/19 had a disproportionately negative impact on some of the representative individuals examined within the different sectors. The projections indicate that while each of the sectors as a whole would continue to make profits largely proportional to their allocation under the different TAC scenarios, many vessel owners in the fishery are likely to face economic losses or very marginal gains under the lower quota options, while the NPV for quota holders who outsource the catching of their quota are likely to be proportionally less affected by the changes in global TAC. This dynamic is important to consider for the future of this fishery. If the resource is to recover, and fishing activity is to continue equitably under the decreased quotas that the recovery of the biomass necessitates, the socio-economic context and the dynamics within which the fishers operate must be considered and studied more extensively and socio-economic consequences of a lower global TAC mitigated while improving the ecological status of the resource. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10
Reef fish associations with benthic habitats at a remote protected coral reef ecosystem in the Western Indian Ocean-Aldabra Atoll, Seychelles
- Authors: Haupt, Philip
- Date: 2020
- Subjects: Coral reef ecology -- Aldabra Islands (Seychelles) , Reef fishes -- Aldabra Islands (Seychelles) , Benthic animals -- Aldabra Islands (Seychelles)
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/141629 , vital:37991
- Description: The aim of the thesis is to develop an understanding of the associations between reef fish and benthic habitats and assess the modifying effects of environmental processes on these relationships at Aldabra, a pristine atoll in the Western Indian Ocean (WIO). Conducting research in pristine, or reference coral reef ecosystem, removes the impact of direct anthropogenic disturbances and provides essential information on natural ecosystem structure and functioning. Three primary hypotheses were tested: 1) Environmental drivers such as depth and exposure to wave energy determine the spatial distribution of benthic habitats; 2) The reef fish assemblage structure is explained by habitat at multiple scales and modified by the effects of environmental drivers such as depth, wave energy and cyclical temporal drivers such as time and tides; 3) The reef fish assemblage at Aldabra represents a pristine reef fish assemblage, comprising high levels of herbivores and predators. The research focussed on the benthic habitat on the seaward reefs between the shoreline and 50 m depth. The first objective was to characterise the benthic habitats on Aldabra Atoll’s seaward reefs and map their spatial distributions using remotely sensed imagery and ground truthing data. The second was to assess the influence of depth and exposure to wave energy on the distribution of benthic habitats. The third was to identify the most suitable standardised method to survey the reef fish assemblage structure on Aldabra’s, and fourth to determine the effect of tide and time of day on the reef fish assemblage. The fifth objective was to establish the association between reef fish assemblage structure and benthic habitats and to test how species-size influenced the scale of habitat at which the associations were most apparent. Four categories of geomorphic reef zones (reef flats (19.2 km2), top of the forereef slope (7.8 km2), deep forereef slope (11.6 km2), and reef platform (14.3 km2)) were manually delineated following the visual outlines of reef features from satellite imagery. The six broad-scale and twelve fine-scale benthic habitats were mapped using a supervised maximum likelihood classification and the spatial coverage of each determined. The broad-scale habitats were 1) Epilithic algal matrix, 2) Hard and soft (coral, 3) Rubble, 4) Macroalgae, 5) Seagrass and 6) Sand. Similarly, twelve fine-scale benthic habitats were characterised and mapped, for example, Hard coral (19 %) including massive and submassive forms with Millepora and Rhytisma. The broad-scale benthic habitat map had an overall producer accuracy of 54 % and fine-scale habitat map 29 %, which was consistent with studies using similar habitat classification methods. The prevailing wave energy, depth and the directional orientation of coral reefs (aspect) significantly influenced the probability of occurrence of each of the broad-scale benthic habitats, and there was a shift in peak probability of occurrence of all habitat categories to a greater depth with an increase in wave energy. The strong relationship of benthic habitats with depth and wave energy suggests that the distributions of benthic habitats are likely to change with sea-level rise and increased intensity and frequency of storms in future. Overall, 338 fish species from 51 families, including 14 species of elasmobranch were recorded using Baited Remote Underwater Video systems (BRUVs) and unbaited Remote Underwater Video systems (RUVS) from 231 samples. Fish were significantly more abundant when observed using BRUVs (119 ± 7) relative to RUVs (92 ± 7), and the assemblage structures were significantly different between the two sampling methods. Abundance and species richness of generalist carnivores and piscivores were significantly greater in BRUVs, while RUVs recorded significantly greater numbers of herbivores and more species of herbivore and corallivore. The results suggest that BRUVs are better suited when studying predatory fish which may not be detected without bait. However, when surveying a taxonomically and functionally diverse assemblage of fishes at a pristine reef, RUVs may provide a more accurate estimate of natural reef fish assemblage structure. Reef fish assemblages observed using RUVs were significantly different between morning-high-tide, midday-low-tide and evening-high-tide for all trophic groups. However, the reef fish assemblage structure observed using BRUVs was insensitive to change in tide and time of day, which may be explained by the attraction effect of bait dampening the effect of tide and time of day. While RUVs appear better to detect more subtle variations in fish assemblage structure, care needs to be taken when designing research programmes that use RUVs, as the sampling design should account for tide and time of day to avoid misinterpreting the cyclical variation, which may confound results. Reef fish assemblages were significantly different among habitats within geomorphic reef zones, broad-scale and fine-scale habitats. Species turnover rates were significantly different for all Actinopterygii size-class categories between the three scales of habitat. No marked differences in species turnover rates among habitats were detected for the majority of Elasmobranch size-class categories. The strong habitat dependency over various spatial scales indicates that effective conservation of Actinopterygii fish at Aldabra, and elsewhere in similar ecosystems requires protection of representative sets of benthic habitats. However, Elasmobranch conservation requires sufficiently large areas as these species utilise multiple habitats, over multiple scales, which are likely to exceed the confines of Aldabra’s reef.
- Full Text:
- Date Issued: 2020
- Authors: Haupt, Philip
- Date: 2020
- Subjects: Coral reef ecology -- Aldabra Islands (Seychelles) , Reef fishes -- Aldabra Islands (Seychelles) , Benthic animals -- Aldabra Islands (Seychelles)
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/141629 , vital:37991
- Description: The aim of the thesis is to develop an understanding of the associations between reef fish and benthic habitats and assess the modifying effects of environmental processes on these relationships at Aldabra, a pristine atoll in the Western Indian Ocean (WIO). Conducting research in pristine, or reference coral reef ecosystem, removes the impact of direct anthropogenic disturbances and provides essential information on natural ecosystem structure and functioning. Three primary hypotheses were tested: 1) Environmental drivers such as depth and exposure to wave energy determine the spatial distribution of benthic habitats; 2) The reef fish assemblage structure is explained by habitat at multiple scales and modified by the effects of environmental drivers such as depth, wave energy and cyclical temporal drivers such as time and tides; 3) The reef fish assemblage at Aldabra represents a pristine reef fish assemblage, comprising high levels of herbivores and predators. The research focussed on the benthic habitat on the seaward reefs between the shoreline and 50 m depth. The first objective was to characterise the benthic habitats on Aldabra Atoll’s seaward reefs and map their spatial distributions using remotely sensed imagery and ground truthing data. The second was to assess the influence of depth and exposure to wave energy on the distribution of benthic habitats. The third was to identify the most suitable standardised method to survey the reef fish assemblage structure on Aldabra’s, and fourth to determine the effect of tide and time of day on the reef fish assemblage. The fifth objective was to establish the association between reef fish assemblage structure and benthic habitats and to test how species-size influenced the scale of habitat at which the associations were most apparent. Four categories of geomorphic reef zones (reef flats (19.2 km2), top of the forereef slope (7.8 km2), deep forereef slope (11.6 km2), and reef platform (14.3 km2)) were manually delineated following the visual outlines of reef features from satellite imagery. The six broad-scale and twelve fine-scale benthic habitats were mapped using a supervised maximum likelihood classification and the spatial coverage of each determined. The broad-scale habitats were 1) Epilithic algal matrix, 2) Hard and soft (coral, 3) Rubble, 4) Macroalgae, 5) Seagrass and 6) Sand. Similarly, twelve fine-scale benthic habitats were characterised and mapped, for example, Hard coral (19 %) including massive and submassive forms with Millepora and Rhytisma. The broad-scale benthic habitat map had an overall producer accuracy of 54 % and fine-scale habitat map 29 %, which was consistent with studies using similar habitat classification methods. The prevailing wave energy, depth and the directional orientation of coral reefs (aspect) significantly influenced the probability of occurrence of each of the broad-scale benthic habitats, and there was a shift in peak probability of occurrence of all habitat categories to a greater depth with an increase in wave energy. The strong relationship of benthic habitats with depth and wave energy suggests that the distributions of benthic habitats are likely to change with sea-level rise and increased intensity and frequency of storms in future. Overall, 338 fish species from 51 families, including 14 species of elasmobranch were recorded using Baited Remote Underwater Video systems (BRUVs) and unbaited Remote Underwater Video systems (RUVS) from 231 samples. Fish were significantly more abundant when observed using BRUVs (119 ± 7) relative to RUVs (92 ± 7), and the assemblage structures were significantly different between the two sampling methods. Abundance and species richness of generalist carnivores and piscivores were significantly greater in BRUVs, while RUVs recorded significantly greater numbers of herbivores and more species of herbivore and corallivore. The results suggest that BRUVs are better suited when studying predatory fish which may not be detected without bait. However, when surveying a taxonomically and functionally diverse assemblage of fishes at a pristine reef, RUVs may provide a more accurate estimate of natural reef fish assemblage structure. Reef fish assemblages observed using RUVs were significantly different between morning-high-tide, midday-low-tide and evening-high-tide for all trophic groups. However, the reef fish assemblage structure observed using BRUVs was insensitive to change in tide and time of day, which may be explained by the attraction effect of bait dampening the effect of tide and time of day. While RUVs appear better to detect more subtle variations in fish assemblage structure, care needs to be taken when designing research programmes that use RUVs, as the sampling design should account for tide and time of day to avoid misinterpreting the cyclical variation, which may confound results. Reef fish assemblages were significantly different among habitats within geomorphic reef zones, broad-scale and fine-scale habitats. Species turnover rates were significantly different for all Actinopterygii size-class categories between the three scales of habitat. No marked differences in species turnover rates among habitats were detected for the majority of Elasmobranch size-class categories. The strong habitat dependency over various spatial scales indicates that effective conservation of Actinopterygii fish at Aldabra, and elsewhere in similar ecosystems requires protection of representative sets of benthic habitats. However, Elasmobranch conservation requires sufficiently large areas as these species utilise multiple habitats, over multiple scales, which are likely to exceed the confines of Aldabra’s reef.
- Full Text:
- Date Issued: 2020