Evaluating and predicting impacts of Australian redclaw crayfish Cherax quadricarinatus and Louisiana red swamp crayfish Procambarus clarkii invasions
- Madzivanzira, Takudzwa Comfort
- Authors: Madzivanzira, Takudzwa Comfort
- Date: 2021-10-29
- Subjects: Cherax Africa , Procambarus clarkii Africa , Freshwater crabs Africa , Crayfish Zambezi River , Crayfish Food Zambezi River , Aquatic biodiversity Africa , Conservation biology Zambezi River , Fishing Catch effort Africa , Introduced freshwater organisms Africa , Fish populations Africa , Functional response (FR)
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191137 , vital:45064 , 10.21504/10962/191137
- Description: Freshwater crayfish have become one of the most widely introduced freshwater taxa globally. Crayfish introductions have not spared the African continent, which, apart from Madagascar, is naturally devoid of native freshwater crayfish. These introductions are of concern because invasive crayfish have generally been shown to cause strong impacts on recipient ecosystems outside Africa. This study therefore set out to compile up-to-date information regarding crayfish introductions in Africa, their pathways and distributions and to improve our understanding of the nature and magnitude of their environmental impacts. A systematic review revealed that nine crayfish species have been introduced into the continent with five of those, Astacus astacus, Cherax quadricarinatus, Faxonius limosus, Procambarus clarkii and Procambarus virginalis, having established naturalised populations in fourteen African countries (Chapter 2). The main driver of these crayfish introductions was to provide socio-economic benefits but there is limited evidence of success. The thesis further documents attempts made to address crayfish knowledge gaps in Africa, including standardisation of C. quadricarinatus sampling gear (Chapter 3), determination of the distribution of C. quadricarinatus in the recently invaded Upper Zambezi Basin (Chapter 4), and predicting ecological and socioeconomic impacts of two crayfish species that are spreading rapidly in Southern Africa, namely, C. quadricarinatus and P. clarkii (Chapters 5 – 8). To standardise C. quadricarinatus sampling methods in Africa, two methods used in Southern Africa were compared and the Promar® collapsible trap baited with dry pellets was recommended as the best approach for C. quadricarinatus abundance studies due to the high catch per unit effort (CPUE), probability of capture and the suitability of dry dog food as a standard bait. This standard approach was used for crayfish surveys in the Zambezi Basin to comprehensively determine the spread and establishment of C. quadricarinatus across the basin. The establishment of C. quadricarinatus in the Barotse Floodplain, Upper Zambezi Floodplains freshwater ecoregion was confirmed. Although the probability of capture and catch per unit effort (CPUE) of C. quadricarinatus in the Barotse floodplain were similar to that of older invasions in the basin (Lake Kariba and Kafue River), morphometric differences among C. quadricarinatus populations sampled from these invaded regions were detected. Although crayfish were not detected in other regions, for example, the Okavango Floodplains ecoregions, C. quadricarinatus have the potential to spread at a downstream and upstream rate of 49 and 12 km·year-1, impacting native biota therein. To evaluate the potential for ecological impacts, the consumer-resource dynamics of C. quadricarinatus and P. clarkii were described in comparison to a native trophic analogue, the freshwater crab of the Potamonautes genus, preying on various native taxa ubiquitous to African aquatic and terrestrial ecosystems. The use of functional response (FR) and consumption experiments in this study showed the potential impacts of the two crayfish species on native resources and on resources that support livelihoods in invaded ecosystems. This in most cases was a result of their high attack parameter, which also resulted in high functional responses ratios (FRRs) compared to native crabs. The crayfish FR, FRRs and consumption rates were mostly enhanced under the high temperature treatments. The FRs and consumption results were then combined with the field biomasses of crayfish and crabs to calculate the relative impact potential (RIP) to successfully predict the degree of impact caused by crayfish species relative to crabs. Crayfish species consistently displayed RIP scores > 1 relative to the native crab irrespective of region, which were higher for the summer than the winter season, suggesting greater impact of the invaders compared to the native species. This study further estimated the socioeconomic losses due to catch spoilage by C. quadricarinatus which are up to 1500 t per year in the invaded Kafue River Basin, which translates to an annual income loss of US$ 2 million. Information provided in this study is vital for conservation management and to compel policymakers to develop appropriate conservation management tools within regulatory frameworks, which could stop or minimise the spread of crayfish species and protect Africa from further losing aquatic biodiversity. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Madzivanzira, Takudzwa Comfort
- Date: 2021-10-29
- Subjects: Cherax Africa , Procambarus clarkii Africa , Freshwater crabs Africa , Crayfish Zambezi River , Crayfish Food Zambezi River , Aquatic biodiversity Africa , Conservation biology Zambezi River , Fishing Catch effort Africa , Introduced freshwater organisms Africa , Fish populations Africa , Functional response (FR)
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191137 , vital:45064 , 10.21504/10962/191137
- Description: Freshwater crayfish have become one of the most widely introduced freshwater taxa globally. Crayfish introductions have not spared the African continent, which, apart from Madagascar, is naturally devoid of native freshwater crayfish. These introductions are of concern because invasive crayfish have generally been shown to cause strong impacts on recipient ecosystems outside Africa. This study therefore set out to compile up-to-date information regarding crayfish introductions in Africa, their pathways and distributions and to improve our understanding of the nature and magnitude of their environmental impacts. A systematic review revealed that nine crayfish species have been introduced into the continent with five of those, Astacus astacus, Cherax quadricarinatus, Faxonius limosus, Procambarus clarkii and Procambarus virginalis, having established naturalised populations in fourteen African countries (Chapter 2). The main driver of these crayfish introductions was to provide socio-economic benefits but there is limited evidence of success. The thesis further documents attempts made to address crayfish knowledge gaps in Africa, including standardisation of C. quadricarinatus sampling gear (Chapter 3), determination of the distribution of C. quadricarinatus in the recently invaded Upper Zambezi Basin (Chapter 4), and predicting ecological and socioeconomic impacts of two crayfish species that are spreading rapidly in Southern Africa, namely, C. quadricarinatus and P. clarkii (Chapters 5 – 8). To standardise C. quadricarinatus sampling methods in Africa, two methods used in Southern Africa were compared and the Promar® collapsible trap baited with dry pellets was recommended as the best approach for C. quadricarinatus abundance studies due to the high catch per unit effort (CPUE), probability of capture and the suitability of dry dog food as a standard bait. This standard approach was used for crayfish surveys in the Zambezi Basin to comprehensively determine the spread and establishment of C. quadricarinatus across the basin. The establishment of C. quadricarinatus in the Barotse Floodplain, Upper Zambezi Floodplains freshwater ecoregion was confirmed. Although the probability of capture and catch per unit effort (CPUE) of C. quadricarinatus in the Barotse floodplain were similar to that of older invasions in the basin (Lake Kariba and Kafue River), morphometric differences among C. quadricarinatus populations sampled from these invaded regions were detected. Although crayfish were not detected in other regions, for example, the Okavango Floodplains ecoregions, C. quadricarinatus have the potential to spread at a downstream and upstream rate of 49 and 12 km·year-1, impacting native biota therein. To evaluate the potential for ecological impacts, the consumer-resource dynamics of C. quadricarinatus and P. clarkii were described in comparison to a native trophic analogue, the freshwater crab of the Potamonautes genus, preying on various native taxa ubiquitous to African aquatic and terrestrial ecosystems. The use of functional response (FR) and consumption experiments in this study showed the potential impacts of the two crayfish species on native resources and on resources that support livelihoods in invaded ecosystems. This in most cases was a result of their high attack parameter, which also resulted in high functional responses ratios (FRRs) compared to native crabs. The crayfish FR, FRRs and consumption rates were mostly enhanced under the high temperature treatments. The FRs and consumption results were then combined with the field biomasses of crayfish and crabs to calculate the relative impact potential (RIP) to successfully predict the degree of impact caused by crayfish species relative to crabs. Crayfish species consistently displayed RIP scores > 1 relative to the native crab irrespective of region, which were higher for the summer than the winter season, suggesting greater impact of the invaders compared to the native species. This study further estimated the socioeconomic losses due to catch spoilage by C. quadricarinatus which are up to 1500 t per year in the invaded Kafue River Basin, which translates to an annual income loss of US$ 2 million. Information provided in this study is vital for conservation management and to compel policymakers to develop appropriate conservation management tools within regulatory frameworks, which could stop or minimise the spread of crayfish species and protect Africa from further losing aquatic biodiversity. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10-29
Aspects of the ecology of the estuarine round-herring Gilchristella aestuaria (Pisces: Clupeidae) and its small-scale fishery potential
- Zvavahera, Munetsi https://orcid.org/0000-0002-5337-1943
- Authors: Zvavahera, Munetsi https://orcid.org/0000-0002-5337-1943
- Date: 2021-05
- Subjects: Small-scale fisheries , Silversides
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10353/22765 , vital:52752
- Description: In the past two decades, there has been increasing pressure for small-scale inland fisheries to play a central role in food and nutrient security for poor communities in South Africa. For decades, South African inland fisheries have focussed on the exploitation of large fish species and generally ignored the exploitation of inland small fish species (SFS). This research aimed to assess the ecology and small-scale fishery potential of the estuarine round-herring, Gilchristella aestuaria. To understand the ecology of G. aestuaria better, morphometric trait analysis and fish condition of populations in relation to environmental variables (salinity, pH, temperature, turbidity and chlorophyll-a) were done. Fish were supplemented with samples acquired from the SAIAB collection facility for 14 sites to cover all the three South African biogeographic regions, stretching from Lake Sibaya (KZN) to the Orange River estuary in the western parts of the country. The morphometric trait analysis showed that G. aestuaria populations can be distinguished based on the trait variation, however there were many overlaps for populations that are interconnected, with distant/ geographically separated populations showing clear differences. Morphometric traits of the G. aestuaria population were significantly different, however there was no strong directional relationship with environmental variables and variation in morphometric traits. However, fish condition as measured by Fulton’s condition (K) and relative weight (Wr) showed variation between populations found in different environments. These differences suggest that these populations must be managed differently if G. aestuaria is to be exploited in managed fisheries. To determine the potential nutrient value of G. aestuaria to the human diet, samples from two freshwater sites and five estuarine sites were analysed for essential macro and micronutrients. The nutrient content of G. aestuaria revealed there is potential for exploitation, as the species has a high macro (protein and fat) and micronutrient composition (calcium, iron and zinc). Mean ± SD of selected nutrients were protein (61.7±5.0 g/100g), fat (20.4±3.7g/ 100g), calcium (3507.5±314.0mg), iron (40.37±14.0mg/ 100g), zinc (22.47±5.6mg/ 100) and vitamin A (37.3±44.4 RAE/ 100g). The nutrient composition of fish collected from freshwater sites was comparable to those collected from estuarine environments. Using the recommended dietary allowances (RDA) from literature, the mass of fish and the number of fish that would provide a minimum amount for each nutrient were calculated. A child would require only 13.4g of dry G. aestuaria or approximately 74 dried fish to meet the daily requirements of zinc. Other minerals such as iron and calcium also showed a similar low weight or number of fish required to meet daily requirements for the different categories. A small number of G. aestuaria are needed to meet RDA for groups (children, adult men, adult women, pregnant women and lactating mothers). A comparison was done for the nutrient composition of G. aestuaria with reference species that are already harvested for human consumption in some African and Asian countries. The protein content of G. aestuaria was comparable to Chisense (Microthrissa moeruensis) and Kapenta Limnothrissa miodon), while the fat composition was more than twice Chisense and Kapenta. Comparing the mineral composition, G. aestuaria had more than three times higher calcium than Mola (Amblypharyngodon mola) and Puti (Puntius sophore). Zinc composition was four times higher than M. moeruensis and L. miodon. Further exploration of the ecology of G. aestuaria was studied using the Sundays River irrigations ponds as a case study that would represent small impoundments across South Africa. Species rank abundance curve and catch per unit effort (CPUE) on the Sundays Irrigation ponds revealed that G. aestuaria dominated numerically and biomass in the Sundays River irrigation ponds. To assess the potential of harvesting G. aestuaria harvesting experiments were conducted using depletion (removal) sampling. Catchweight (kg) ranged from 2.16 (1.03; 3.28) to 61.25 (44.40; 78.09) kg and the estimated biomass from the depletion model ranged from 1.05 to 40.19 kg/ha for September 2019. The depletion model revealed that small impoundments have high biomass per hectare of G. aestuaria ranging from which indicates that the species may not support a commercial fishery but small-scale fisheries. In conclusion, G. aestuaria could become a meaningful contribution to the food and nutrient security of poor communities where available as a food source through small-scale fishery exploitation. The extent of this contribution may depend on its production potential in various regions and environments. More research is however needed to determine the long-term sustainability of harvesting of G aestuaria by looking at how populations respond to harvesting. , Thesis (PhD) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-05
- Authors: Zvavahera, Munetsi https://orcid.org/0000-0002-5337-1943
- Date: 2021-05
- Subjects: Small-scale fisheries , Silversides
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10353/22765 , vital:52752
- Description: In the past two decades, there has been increasing pressure for small-scale inland fisheries to play a central role in food and nutrient security for poor communities in South Africa. For decades, South African inland fisheries have focussed on the exploitation of large fish species and generally ignored the exploitation of inland small fish species (SFS). This research aimed to assess the ecology and small-scale fishery potential of the estuarine round-herring, Gilchristella aestuaria. To understand the ecology of G. aestuaria better, morphometric trait analysis and fish condition of populations in relation to environmental variables (salinity, pH, temperature, turbidity and chlorophyll-a) were done. Fish were supplemented with samples acquired from the SAIAB collection facility for 14 sites to cover all the three South African biogeographic regions, stretching from Lake Sibaya (KZN) to the Orange River estuary in the western parts of the country. The morphometric trait analysis showed that G. aestuaria populations can be distinguished based on the trait variation, however there were many overlaps for populations that are interconnected, with distant/ geographically separated populations showing clear differences. Morphometric traits of the G. aestuaria population were significantly different, however there was no strong directional relationship with environmental variables and variation in morphometric traits. However, fish condition as measured by Fulton’s condition (K) and relative weight (Wr) showed variation between populations found in different environments. These differences suggest that these populations must be managed differently if G. aestuaria is to be exploited in managed fisheries. To determine the potential nutrient value of G. aestuaria to the human diet, samples from two freshwater sites and five estuarine sites were analysed for essential macro and micronutrients. The nutrient content of G. aestuaria revealed there is potential for exploitation, as the species has a high macro (protein and fat) and micronutrient composition (calcium, iron and zinc). Mean ± SD of selected nutrients were protein (61.7±5.0 g/100g), fat (20.4±3.7g/ 100g), calcium (3507.5±314.0mg), iron (40.37±14.0mg/ 100g), zinc (22.47±5.6mg/ 100) and vitamin A (37.3±44.4 RAE/ 100g). The nutrient composition of fish collected from freshwater sites was comparable to those collected from estuarine environments. Using the recommended dietary allowances (RDA) from literature, the mass of fish and the number of fish that would provide a minimum amount for each nutrient were calculated. A child would require only 13.4g of dry G. aestuaria or approximately 74 dried fish to meet the daily requirements of zinc. Other minerals such as iron and calcium also showed a similar low weight or number of fish required to meet daily requirements for the different categories. A small number of G. aestuaria are needed to meet RDA for groups (children, adult men, adult women, pregnant women and lactating mothers). A comparison was done for the nutrient composition of G. aestuaria with reference species that are already harvested for human consumption in some African and Asian countries. The protein content of G. aestuaria was comparable to Chisense (Microthrissa moeruensis) and Kapenta Limnothrissa miodon), while the fat composition was more than twice Chisense and Kapenta. Comparing the mineral composition, G. aestuaria had more than three times higher calcium than Mola (Amblypharyngodon mola) and Puti (Puntius sophore). Zinc composition was four times higher than M. moeruensis and L. miodon. Further exploration of the ecology of G. aestuaria was studied using the Sundays River irrigations ponds as a case study that would represent small impoundments across South Africa. Species rank abundance curve and catch per unit effort (CPUE) on the Sundays Irrigation ponds revealed that G. aestuaria dominated numerically and biomass in the Sundays River irrigation ponds. To assess the potential of harvesting G. aestuaria harvesting experiments were conducted using depletion (removal) sampling. Catchweight (kg) ranged from 2.16 (1.03; 3.28) to 61.25 (44.40; 78.09) kg and the estimated biomass from the depletion model ranged from 1.05 to 40.19 kg/ha for September 2019. The depletion model revealed that small impoundments have high biomass per hectare of G. aestuaria ranging from which indicates that the species may not support a commercial fishery but small-scale fisheries. In conclusion, G. aestuaria could become a meaningful contribution to the food and nutrient security of poor communities where available as a food source through small-scale fishery exploitation. The extent of this contribution may depend on its production potential in various regions and environments. More research is however needed to determine the long-term sustainability of harvesting of G aestuaria by looking at how populations respond to harvesting. , Thesis (PhD) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-05
Evaluation of Baited Remote Underwater Video Systems (BRUVS) for monitoring fish communities in Lake Malawi/Niassa
- Authors: Van Wyk, Angus
- Date: 2020
- Subjects: Underwater videography -- Malawi , Chambo -- Malawi -- Monitoring , Fishes -- Malawi -- Monitoring , Oreochromis lidole -- Malawi -- Monitoring
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145546 , vital:38448
- Description: Baited Remote Underwater Video systems (BRUVS) have become a well-established in-situ monitoring technique in clearwater aquatic ecosystems. The relatively low cost, nondestructive and non-extractive nature of this technique permits BRUVS to be employed in a wide range of habitats. To date, the vast majority of studies using BRUVS technology have been conducted in marine habitats. Subsequently, BRUVS applications in freshwater habitats are scant, and techniques are not well developed. The primary objective of this thesis was to address this knowledge gap and develop standard operating procedures for BRUVS employment in Lake Malawi/Niassa and explore the potential of BRUVS as a monitoring tool for fish communities in the African Great Lakes. Eight easily identifiable species groups, representative of Lake Malawi/Niassa inshore fish communities, were used to develop the technique. The optimal BRUVS deployment time to obtain 95 % species accumulation was achieved in a 15-minute recording period. Power analysis, using a pre-determined 80 % power, a confidence interval of 95 % and a significance level of < 0.05 was used to determine annual sampling effort requirements for each species group. The power analysis was performed to detect a 10 % change in abundance over a hypothetical 10-year monitoring scenario. In areas where fish abundance was lower, the sampling effort required to monitor key fisheries species was significantly higher. For example, Chambo, the local Oreochromis (Nyasalapia) species flock, required an annual sampling effort of 120 deployments in Malawi compared to 56 in Mozambique ( < 0.05). Chambo had a higher detection probability in areas of lesser fishing pressure and were found in higher abundances in deeper, less accessible habitats. Deep-water (> 20 m) and rocky habitats were most important in explaining Chambo abundance and detection probability. The size-structure of Chambo in Lake Malawi/Niassa reflects size-specific depth and habitat migrations. Larger Chambo were observed aggregating in waters deeper than 20 m and a broader size range of individuals were observed utilising structured habitat. The effects of fishing are apparent in the size-structure of Chambo in the areas sampled. In study areas exposed to greater levels of fishing pressure – such as Malawi, the BRUVS detected significantly fewer individuals within sexually mature size classes, and the average size was smaller than in areas with less exploitation.
- Full Text:
- Date Issued: 2020
- Authors: Van Wyk, Angus
- Date: 2020
- Subjects: Underwater videography -- Malawi , Chambo -- Malawi -- Monitoring , Fishes -- Malawi -- Monitoring , Oreochromis lidole -- Malawi -- Monitoring
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145546 , vital:38448
- Description: Baited Remote Underwater Video systems (BRUVS) have become a well-established in-situ monitoring technique in clearwater aquatic ecosystems. The relatively low cost, nondestructive and non-extractive nature of this technique permits BRUVS to be employed in a wide range of habitats. To date, the vast majority of studies using BRUVS technology have been conducted in marine habitats. Subsequently, BRUVS applications in freshwater habitats are scant, and techniques are not well developed. The primary objective of this thesis was to address this knowledge gap and develop standard operating procedures for BRUVS employment in Lake Malawi/Niassa and explore the potential of BRUVS as a monitoring tool for fish communities in the African Great Lakes. Eight easily identifiable species groups, representative of Lake Malawi/Niassa inshore fish communities, were used to develop the technique. The optimal BRUVS deployment time to obtain 95 % species accumulation was achieved in a 15-minute recording period. Power analysis, using a pre-determined 80 % power, a confidence interval of 95 % and a significance level of < 0.05 was used to determine annual sampling effort requirements for each species group. The power analysis was performed to detect a 10 % change in abundance over a hypothetical 10-year monitoring scenario. In areas where fish abundance was lower, the sampling effort required to monitor key fisheries species was significantly higher. For example, Chambo, the local Oreochromis (Nyasalapia) species flock, required an annual sampling effort of 120 deployments in Malawi compared to 56 in Mozambique ( < 0.05). Chambo had a higher detection probability in areas of lesser fishing pressure and were found in higher abundances in deeper, less accessible habitats. Deep-water (> 20 m) and rocky habitats were most important in explaining Chambo abundance and detection probability. The size-structure of Chambo in Lake Malawi/Niassa reflects size-specific depth and habitat migrations. Larger Chambo were observed aggregating in waters deeper than 20 m and a broader size range of individuals were observed utilising structured habitat. The effects of fishing are apparent in the size-structure of Chambo in the areas sampled. In study areas exposed to greater levels of fishing pressure – such as Malawi, the BRUVS detected significantly fewer individuals within sexually mature size classes, and the average size was smaller than in areas with less exploitation.
- Full Text:
- Date Issued: 2020
Understanding biotic interactions in invaded pond communities in the Sundays River irrigation network, South Africa
- Authors: Mofu, Lubabalo
- Date: 2020
- Subjects: Mozambique tilapia -- South Africa -- Sundays River (Eastern Cape) , Western mosquitofish -- South Africa -- Sundays River (Eastern Cape) , Gobiidae -- South Africa -- Sundays River (Eastern Cape) , Clupeidae -- South Africa -- Sundays River (Eastern Cape) , Reservoirs -- South Africa -- Sundays River (Eastern Cape) , Zooplankton -- South Africa -- Sundays River (Eastern Cape) , Freshwater ecology -- South Africa -- Sundays River (Eastern Cape) , Biotic communities -- South Africa -- Sundays River (Eastern Cape) , Fishes -- Effect of temperature on -- South Africa -- Sundays River (Eastern Cape) , Stable isotopes , Relative Impact Potential
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167089 , vital:41436
- Description: The Sundays River valley irrigation ponds provide a unique opportunity to investigate biotic interactions within a biological invasions context, as they contain both native and non-native fish species. This study focusses on two native species (Glossogobius callidus and Gilchristella aestuaria) and two non-native species (Oreochromis mossambicus and Gambusia affinis). The ecology of the ponds was driven by physico-chemical variables, mainly temperature, but the interactions between fishes were a complex interplay between temperature, pond community ecology and food web structure. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Chlorophyll-a, temperature, G. callidus and G. affinis were the drivers of the seasonal changes in macroinvertebrate composition. Stable isotope analysis identified substantial ontogenetic dietary shifts in all species, corresponding to changes in body size. Stable isotope analysis revealed that the niche space occupied by G. affinis was broad and overlapped with that of the other three focal species. Stable isotope metrics showed that G. affinis and O. mossambicus utilised a wide range of resources compared to G. callidus and G. aestuaria. Stomach content analysis showed that G. callidus, O. mossambicus and G. affinis fed predominantly on benthic resources, while G. aestuaria fed mainly plankton resources. Functional response experiments revealed that G. callidus and G. affinis both displayed Type II functional responses. In single fish trials, G. affinis had significantly higher functional responses than G. callidus. In heterospecific G. callidus-G. affinis combinations the functional response of G. callidus was reduced by the presence of G. affinis, whereas, this combination greatly enhanced G. affinis functional response magnitudes. The functional response of G. callidus, O. mossambicus and G. affinis under two temperature treatments along with fish abundance data was used to determine temporal differences in the ecological impacts of each fish species between seasons. The relative impact potential of O. mossambicus was consistently higher than that of G. callidus and G. affinis. This study demonstrates how seasonal temperature fluctuations affect the relative impact capacities of introduced species. Overall, this thesis showed that high temperature along with life-history traits contributes to the biotic interactions between native and non-native species in novel environments.
- Full Text:
- Date Issued: 2020
- Authors: Mofu, Lubabalo
- Date: 2020
- Subjects: Mozambique tilapia -- South Africa -- Sundays River (Eastern Cape) , Western mosquitofish -- South Africa -- Sundays River (Eastern Cape) , Gobiidae -- South Africa -- Sundays River (Eastern Cape) , Clupeidae -- South Africa -- Sundays River (Eastern Cape) , Reservoirs -- South Africa -- Sundays River (Eastern Cape) , Zooplankton -- South Africa -- Sundays River (Eastern Cape) , Freshwater ecology -- South Africa -- Sundays River (Eastern Cape) , Biotic communities -- South Africa -- Sundays River (Eastern Cape) , Fishes -- Effect of temperature on -- South Africa -- Sundays River (Eastern Cape) , Stable isotopes , Relative Impact Potential
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167089 , vital:41436
- Description: The Sundays River valley irrigation ponds provide a unique opportunity to investigate biotic interactions within a biological invasions context, as they contain both native and non-native fish species. This study focusses on two native species (Glossogobius callidus and Gilchristella aestuaria) and two non-native species (Oreochromis mossambicus and Gambusia affinis). The ecology of the ponds was driven by physico-chemical variables, mainly temperature, but the interactions between fishes were a complex interplay between temperature, pond community ecology and food web structure. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Chlorophyll-a, temperature, G. callidus and G. affinis were the drivers of the seasonal changes in macroinvertebrate composition. Stable isotope analysis identified substantial ontogenetic dietary shifts in all species, corresponding to changes in body size. Stable isotope analysis revealed that the niche space occupied by G. affinis was broad and overlapped with that of the other three focal species. Stable isotope metrics showed that G. affinis and O. mossambicus utilised a wide range of resources compared to G. callidus and G. aestuaria. Stomach content analysis showed that G. callidus, O. mossambicus and G. affinis fed predominantly on benthic resources, while G. aestuaria fed mainly plankton resources. Functional response experiments revealed that G. callidus and G. affinis both displayed Type II functional responses. In single fish trials, G. affinis had significantly higher functional responses than G. callidus. In heterospecific G. callidus-G. affinis combinations the functional response of G. callidus was reduced by the presence of G. affinis, whereas, this combination greatly enhanced G. affinis functional response magnitudes. The functional response of G. callidus, O. mossambicus and G. affinis under two temperature treatments along with fish abundance data was used to determine temporal differences in the ecological impacts of each fish species between seasons. The relative impact potential of O. mossambicus was consistently higher than that of G. callidus and G. affinis. This study demonstrates how seasonal temperature fluctuations affect the relative impact capacities of introduced species. Overall, this thesis showed that high temperature along with life-history traits contributes to the biotic interactions between native and non-native species in novel environments.
- Full Text:
- Date Issued: 2020
Biotic and abiotic drivers of macroinvertebrate assemblages in a South African river
- Authors: Bellingan, Terence Andrew
- Date: 2018
- Subjects: Aquatic insects -- South Africa -- Eastern Cape , Stream ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape , Riparian areas -- Management , Ecosystem management -- South Africa -- Eastern Cape , Mayflies -- South Africa -- Eastern Cape , Stoneflies -- South Africa -- Eastern Cape , Keiskamma River
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61839 , vital:28067
- Description: Aquatic insects are the most numerically abundant and diverse group of organisms found in lotic ecosystems in South Africa and the world over. They play vital roles in freshwater ecosystem functioning, processing nutrients and in turn forming integral links in stream food-webs. This thesis focussed on examining the macroinvertebrate fauna within three reaches of headwater streams of the Keiskamma River system: reaches that were considered to be fishless; reaches that were invaded by non-native salmonid species; and reaches that were dominated by native fish. I described the effects of predatory fish presence through detailed examination of macroinvertebrate assemblage composition; macroinvertebrate drift timing and density; and through niche utilisation determined from stable isotope data. Patterns in the macroinvertebrate assemblages of the headwaters of the Keiskamma River appear to be driven more strongly by flow rate and seasonal influences, but fish presence and biotope availability were also significant drivers. Niche shifts due to predator presence were not easy to detect and, while patterns of influence may have been evident, they were not found to be significant. However, I demonstrated that salmonids selectively feed on native fish species when the opportunity is presented, occupying significantly higher trophic levels when co-occurring with native fish than in invaded reaches where native fish are absent. Drift timing and density were demonstrated to be significantly different between reach for specific macroinvertebrate species from the Ephemeroptera and Plecoptera, under differing fish predation regimes, in agreement with what has been observed from studies in rivers elsewhere. In freshwater ecosystems of South Africa and worldwide, mitigation of negative effects of alien fishes through their removal using piscicides may also affect non-target organisms. To better understand the effects of just such a removal operation, employed for the first time in the history of freshwater conservation in South Africa, macroinvertebrate communities were assessed for non-target effects of rotenone. The fish eradication operations were demonstrated to have a short-term negative effect on the macroinvertebrate assemblage, through water quality index measurements and alteration of densities of macroinvertebrate taxa collected from stone surfaces. However, no long-term detrimental impact was observed as macroinvertebrate faunas returned to a comparable pre-treatment state within a year of each rotenone application.
- Full Text:
- Date Issued: 2018
- Authors: Bellingan, Terence Andrew
- Date: 2018
- Subjects: Aquatic insects -- South Africa -- Eastern Cape , Stream ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape , Riparian areas -- Management , Ecosystem management -- South Africa -- Eastern Cape , Mayflies -- South Africa -- Eastern Cape , Stoneflies -- South Africa -- Eastern Cape , Keiskamma River
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61839 , vital:28067
- Description: Aquatic insects are the most numerically abundant and diverse group of organisms found in lotic ecosystems in South Africa and the world over. They play vital roles in freshwater ecosystem functioning, processing nutrients and in turn forming integral links in stream food-webs. This thesis focussed on examining the macroinvertebrate fauna within three reaches of headwater streams of the Keiskamma River system: reaches that were considered to be fishless; reaches that were invaded by non-native salmonid species; and reaches that were dominated by native fish. I described the effects of predatory fish presence through detailed examination of macroinvertebrate assemblage composition; macroinvertebrate drift timing and density; and through niche utilisation determined from stable isotope data. Patterns in the macroinvertebrate assemblages of the headwaters of the Keiskamma River appear to be driven more strongly by flow rate and seasonal influences, but fish presence and biotope availability were also significant drivers. Niche shifts due to predator presence were not easy to detect and, while patterns of influence may have been evident, they were not found to be significant. However, I demonstrated that salmonids selectively feed on native fish species when the opportunity is presented, occupying significantly higher trophic levels when co-occurring with native fish than in invaded reaches where native fish are absent. Drift timing and density were demonstrated to be significantly different between reach for specific macroinvertebrate species from the Ephemeroptera and Plecoptera, under differing fish predation regimes, in agreement with what has been observed from studies in rivers elsewhere. In freshwater ecosystems of South Africa and worldwide, mitigation of negative effects of alien fishes through their removal using piscicides may also affect non-target organisms. To better understand the effects of just such a removal operation, employed for the first time in the history of freshwater conservation in South Africa, macroinvertebrate communities were assessed for non-target effects of rotenone. The fish eradication operations were demonstrated to have a short-term negative effect on the macroinvertebrate assemblage, through water quality index measurements and alteration of densities of macroinvertebrate taxa collected from stone surfaces. However, no long-term detrimental impact was observed as macroinvertebrate faunas returned to a comparable pre-treatment state within a year of each rotenone application.
- Full Text:
- Date Issued: 2018
The effect of water temperature on the distribution of the Eastern Cape redfin minnow, Pseudobarbus afer (Peters, 1864)
- Authors: Bloy, Lesley Elizabeth
- Date: 2018
- Subjects: Minnows -- South Africa -- Eastern Cape , Cyprinidae -- South Africa -- Eastern Cape , Minnows -- Effect of temperature on -- South Africa -- Eastern Cape , Minnows -- Effect of exotic animals on -- South Africa -- Eastern Cape , Introduced organisms -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62017 , vital:28096
- Description: The main objective of this MSc study was to disentangle whether temperature or the presence of non-native fish was limiting the distribution of Pseudobarbus afer (Peters, 1864) in the Blindekloof stream, Eastern Cape, South Africa. The aims were to: i) describe the thermal regime of the Blindekloof stream; ii) conduct experiments to determine the preferred and critical temperatures of P. afer and; iii) use snorkel surveys to contextualise the distribution of both native and non-native fishes in the Blindekloof stream to assess whether the downstream distribution of P. afer was likely to be influenced by temperature or by the presence of non-native, predatory fishes. To describe the thermal regime, year-long temperature data from four long term monitoring sites in the Blindekloof stream were collected using Hobo temperature loggers and analysed in order to better understand the thermal profile, the thermal variation and the rate of temperature change in the stream. The warmest temperatures were recorded in late December 2015 (absolute maximum of 29.4 °C). The coolest water temperatures were recorded in early August 2015 (absolute minimum of 9.5 °C). There is both seasonal and diel variation in temperature with mean, minimum, maximum, 7 day mean, 7 day maximum and temperature ranges differing significantly between sites. With knowledge of the thermal regime of a monitored reach of the Blindekloof stream, the thermal tolerance and preference of P. afer were investigated. The thermal tolerance of P. afer was investigated using the Critical Thermal Method (CTM) which uses non-lethal endpoints (the loss of equilibrium). At low acclimatization temperatures (11.9 ± 0.7 °C), the mean CTmax of P. afer was found to be 29.9 ± 0.7 °C, while at a higher acclimatization temperature (19.9 ± 0.1 °C), the mean CTmax was 35.1 ± 0.6°C. Custom-built thermal choice tanks were used to investigate the thermal preference of P. afer in both summer and winter. The preferred median temperatures for the summer experiments ranged from 22.4 - 29.3 °C while the winter preferred median temperatures ranged from 18.5 - 23.1 °C. The thermal tolerance of P. afer was compared to the thermal regime of the stream and the results suggest that temperature is not limiting the distribution of P. afer. Snorkel surveys were used to determine the distribution of fishes in the Blindekloof stream. Analysis of the distribution data suggests that, in the absence of non-native predatory species, native fishes have the potential to inhabit pools throughout the system right to the confluence, thus predatory fishes and not temperature was limiting P. afer distributions.
- Full Text:
- Date Issued: 2018
- Authors: Bloy, Lesley Elizabeth
- Date: 2018
- Subjects: Minnows -- South Africa -- Eastern Cape , Cyprinidae -- South Africa -- Eastern Cape , Minnows -- Effect of temperature on -- South Africa -- Eastern Cape , Minnows -- Effect of exotic animals on -- South Africa -- Eastern Cape , Introduced organisms -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62017 , vital:28096
- Description: The main objective of this MSc study was to disentangle whether temperature or the presence of non-native fish was limiting the distribution of Pseudobarbus afer (Peters, 1864) in the Blindekloof stream, Eastern Cape, South Africa. The aims were to: i) describe the thermal regime of the Blindekloof stream; ii) conduct experiments to determine the preferred and critical temperatures of P. afer and; iii) use snorkel surveys to contextualise the distribution of both native and non-native fishes in the Blindekloof stream to assess whether the downstream distribution of P. afer was likely to be influenced by temperature or by the presence of non-native, predatory fishes. To describe the thermal regime, year-long temperature data from four long term monitoring sites in the Blindekloof stream were collected using Hobo temperature loggers and analysed in order to better understand the thermal profile, the thermal variation and the rate of temperature change in the stream. The warmest temperatures were recorded in late December 2015 (absolute maximum of 29.4 °C). The coolest water temperatures were recorded in early August 2015 (absolute minimum of 9.5 °C). There is both seasonal and diel variation in temperature with mean, minimum, maximum, 7 day mean, 7 day maximum and temperature ranges differing significantly between sites. With knowledge of the thermal regime of a monitored reach of the Blindekloof stream, the thermal tolerance and preference of P. afer were investigated. The thermal tolerance of P. afer was investigated using the Critical Thermal Method (CTM) which uses non-lethal endpoints (the loss of equilibrium). At low acclimatization temperatures (11.9 ± 0.7 °C), the mean CTmax of P. afer was found to be 29.9 ± 0.7 °C, while at a higher acclimatization temperature (19.9 ± 0.1 °C), the mean CTmax was 35.1 ± 0.6°C. Custom-built thermal choice tanks were used to investigate the thermal preference of P. afer in both summer and winter. The preferred median temperatures for the summer experiments ranged from 22.4 - 29.3 °C while the winter preferred median temperatures ranged from 18.5 - 23.1 °C. The thermal tolerance of P. afer was compared to the thermal regime of the stream and the results suggest that temperature is not limiting the distribution of P. afer. Snorkel surveys were used to determine the distribution of fishes in the Blindekloof stream. Analysis of the distribution data suggests that, in the absence of non-native predatory species, native fishes have the potential to inhabit pools throughout the system right to the confluence, thus predatory fishes and not temperature was limiting P. afer distributions.
- Full Text:
- Date Issued: 2018
Using action cameras to assess habitat use by Pseudobarbus afer and Sandelia capensis in the Swartkops River, Eastern Cape, South Africa
- Authors: Hannweg, Bianca
- Date: 2018
- Subjects: Freshwater biodiversity -- South Africa -- Eastern Cape , Freshwater biodiversity conservation -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape , Freshwater fishes -- South Africa -- Eastern Cape , Freshwater fishes -- Behavior -- South Africa -- Eastern Cape , Freshwater fishes -- Habitat -- South Africa -- Eastern Cape , Underwater videography , Anabantidae -- South Africa -- Eastern Cape , Cyprinidae -- South Africa -- Eastern Cape , Pseudobarbus afer , Sandelia capensis
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62039 , vital:28098
- Description: Currently, freshwater systems are facing various threats, freshwater biota are declining and there is an increased need to monitor freshwater fauna and flora using non-invasive methods. This thesis aimed to evaluate the potential of using action cameras as a tool for the monitoring of freshwater fish populations and the collection of habitat utilisation data. This evaluation was conducted in headwater tributaries of the Swartkops River in South Africa, using two threatened species that have not been extensively studied, Pseudobarbus afer (Peters, 1864) and Sandelia capensis (Cuvier, 1831). The aims of this study were to: (1) assess the use of underwater video analysis (UWVA) using action cameras (videos and still photographs) in comparison to estimates derived from snorkel surveys, to estimate the abundance of P. afer in headwater streams; (2) use estimates derived from UWVA (videos and photographs) to assess the habitat use of two imperilled species, P. afer and S. capensis; and (3) assess habitat use by these two species in the presence of an artificial habitat. This work demonstrated that: (1) estimates derived from videos and photographs were strongly correlated to estimates derived from snorkel surveys, provided multiple cameras were used; (2) estimates derived from videos and photographs were not significantly different to estimates derived from snorkel surveys; (3) a filming period of 15 minutes was sufficient at detecting 0.9 of the cumulative mMaxN (mean MaxN) within one of the five habitats; and (4) still photographs, which are less time consuming to process than videos, could be used in preference to videos. Based on these findings, techniques using action cameras to assess habitat utilisation and behaviour in situ of the two-focal species, were developed using six habitat types (inflow, outflow, woody debris, fern root, middle and artificial) in four pools. It was demonstrated that: (1) there was a significant difference in proportional occupancies across habitats for both P. afer and S. capensis; (2) Pseudobarbus afer were mainly observed schooling in the middle of the pool and feeding on detritus material in fern root, woody debris and off the artificial structure; and (3) Sandelia capensis rapidly colonised the artificial structure and were observed utilising it for refuge. In conclusion, this work demonstrated that still photographs from action cameras can be used in place of videos to estimate the abundance of freshwater fishes and assess their habitat use and behaviour in clear headwater streams. This work also demonstrated how action cameras could be used to evaluate the effect of the introduction of artificial habitat as a restoration measure for headwater fish communities.
- Full Text:
- Date Issued: 2018
- Authors: Hannweg, Bianca
- Date: 2018
- Subjects: Freshwater biodiversity -- South Africa -- Eastern Cape , Freshwater biodiversity conservation -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape , Freshwater fishes -- South Africa -- Eastern Cape , Freshwater fishes -- Behavior -- South Africa -- Eastern Cape , Freshwater fishes -- Habitat -- South Africa -- Eastern Cape , Underwater videography , Anabantidae -- South Africa -- Eastern Cape , Cyprinidae -- South Africa -- Eastern Cape , Pseudobarbus afer , Sandelia capensis
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62039 , vital:28098
- Description: Currently, freshwater systems are facing various threats, freshwater biota are declining and there is an increased need to monitor freshwater fauna and flora using non-invasive methods. This thesis aimed to evaluate the potential of using action cameras as a tool for the monitoring of freshwater fish populations and the collection of habitat utilisation data. This evaluation was conducted in headwater tributaries of the Swartkops River in South Africa, using two threatened species that have not been extensively studied, Pseudobarbus afer (Peters, 1864) and Sandelia capensis (Cuvier, 1831). The aims of this study were to: (1) assess the use of underwater video analysis (UWVA) using action cameras (videos and still photographs) in comparison to estimates derived from snorkel surveys, to estimate the abundance of P. afer in headwater streams; (2) use estimates derived from UWVA (videos and photographs) to assess the habitat use of two imperilled species, P. afer and S. capensis; and (3) assess habitat use by these two species in the presence of an artificial habitat. This work demonstrated that: (1) estimates derived from videos and photographs were strongly correlated to estimates derived from snorkel surveys, provided multiple cameras were used; (2) estimates derived from videos and photographs were not significantly different to estimates derived from snorkel surveys; (3) a filming period of 15 minutes was sufficient at detecting 0.9 of the cumulative mMaxN (mean MaxN) within one of the five habitats; and (4) still photographs, which are less time consuming to process than videos, could be used in preference to videos. Based on these findings, techniques using action cameras to assess habitat utilisation and behaviour in situ of the two-focal species, were developed using six habitat types (inflow, outflow, woody debris, fern root, middle and artificial) in four pools. It was demonstrated that: (1) there was a significant difference in proportional occupancies across habitats for both P. afer and S. capensis; (2) Pseudobarbus afer were mainly observed schooling in the middle of the pool and feeding on detritus material in fern root, woody debris and off the artificial structure; and (3) Sandelia capensis rapidly colonised the artificial structure and were observed utilising it for refuge. In conclusion, this work demonstrated that still photographs from action cameras can be used in place of videos to estimate the abundance of freshwater fishes and assess their habitat use and behaviour in clear headwater streams. This work also demonstrated how action cameras could be used to evaluate the effect of the introduction of artificial habitat as a restoration measure for headwater fish communities.
- Full Text:
- Date Issued: 2018
Colonisation and succession of fishes in Lake Liambezi, a shallow ephemeral floodplain lake in Southern Africa
- Authors: Peel, Richard Anthony
- Date: 2017
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/65211 , vital:28707
- Description: Expected release date-May 2019
- Full Text:
- Date Issued: 2017
- Authors: Peel, Richard Anthony
- Date: 2017
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/65211 , vital:28707
- Description: Expected release date-May 2019
- Full Text:
- Date Issued: 2017
Comparative fish ecology in three periodically connected rivers in the upper Zambezi and Okavango ecoregions
- Authors: Taylor, Geraldine Claire
- Date: 2017
- Subjects: Fishes Ecology Zambia Zambezi District , Floodplain ecology Zambia Zambezi District , Stable isotopes , Fishes Food Zambia Zambezi District , Fishes Mortality Zambia Zambezi District , Fish populations Zambia Zambezi District , Fishes Growth
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/65055 , vital:28660 , DOI https://doi.org/10.21504/10962/65055
- Description: The Upper Zambezi, Kavango and Kwando rivers are three periodically interlinked floodplain rivers which share the same Upper Zambezian floodplain ichthyofauna. The aim of this thesis was to compare the biology and ecology of the fish communities in these three rivers. The objective was to test the hypothesis that fish community composition and assemblage structure, fish diets, food web structure and trophic dynamics, fish growth rates and total mortality are influenced by the differing flood magnitudes of the three rivers, in support of the flood pulse concept. To understand the abiotic characteristics of each river, water temperature, flood regime, total dissolved inorganic nitrogen concentrations and water quality parameters were measured and compared between rivers. Water temperatures varied seasonally, and seven day moving averages peaked above 30 °C in January, and fell to between 16 and 19 °C in June. The Zambezi River had the largest flood (6.14 m), followed by the Kavango River (3.80 m), while the Kwando River had the smallest flood (0.65 m). Total dissolved inorganic nitrogen concentrations were low in the Kavango and Zambezi Rivers (0.2 - 0.6 mg/l), and slightly higher in the Kwando River (<1 mg/l). Conductivity, total dissolved solids and total dissolved inorganic nitrogen concentrations decreased with the flood (dilution effect). Using biomass catch per unit effort data from experimental gillnets, fish community composition and assemblage structure was described, and differed between rivers in all hydrological seasons. In the Zambezi and Kavango rivers, fish assemblages varied with hydrological season as a result of the homogenising influence of the flood pulse, while in the Kwando River fish assemblages did not differ seasonally as flood pulses were small and often irregular. Differences in community composition were attributed to the abundance of Hydrocynus vittatus, a large bodied open water predator, in the Zambezi and Kavango rivers, and its relative absence in the Kwando River. Based on the results of the community composition, six focus species were chosen that were abundant and representative of the various feeding modes and life history strategies of the fish community. These were the striped robber Brycinus lateralis, sharptooth catfish Clarias gariepinus, blunttooth catfish Clarias ngamensis, African pike Hepsetus cuvieri, silver catfish Schilbe intermedius and purpleface largemouth Serranochromis macrocephalus. Stomach contents analysis was then used to compare the feeding ecology of the six example species between rivers. Clarias gariepinus, C. ngamensis and S. intermedius were piscivorous in the Zambezi and Kavango rivers, and preyed upon more invertebrates in the Kwando River, while Hepsetus cuvieri and S. macrocephalus were piscivorous in all three rivers. Differences in diets were attributed to seasonal prey abundance, with prey fishes abundant during falling and low water when the Zambezi and Kavango rivers were sampled, while invertebrates were abundant during rising and high water when the Kwando River was sampled. Prey mastication by B. lateralis made prey identification difficult. For other predators, the usefulness of stomach contents analysis for dietary descriptions was restricted by the high proportion of empty stomachs. As a result, whole ecosystem stable isotope analysis was used to gain a holistic understanding of the food web structure and fish feeding ecology of the three rivers. The Zambezi and Kavango river food webs were supported by C enriched resources such as C4 and C3 riparian vegetation from the floodplain, while the Kwando River food web was based on C depleted resources such as filamentous algae and aquatic macrophytes. The Zambezi River food web had a restricted nitrogen range, with reduced food chain length and the predators in this river did not occupy such elevated trophic positions compared to in the Kavango and Kwando river food webs. This was attributed to the overfishing of the primary and tertiary consumers in the Zambezi River, a phenomenon known to reduce food chain length. Focussing on predator communities, in the Zambezi and Kavango rivers, H. vittatus isotopic niche width was large and overlapped significantly with most other predators, while in the Kwando River predator niches were more distinct. This supported previously proposed hypotheses by describing H. vittatus as a dominant predator which excludes all other fishes by predation or competition. Despite the dominance of H. vittatus, C. gariepinus occupied the position of top predator in all three rivers, and information on the habitat use, feeding habits and trophic niches of the serranochromine cichlids added understanding of their ecology. Lastly, age was determined using sectioned sagittal otoliths for C. gariepinus, C. ngamensis, S. intermedius and S. macrocephalus and using whole asteriscus otoliths for B. lateralis and H. cuvieri, and growth was modelled using the von Bertalanffy growth equation. Growth performance was high in the Zambezi and Kavango rivers, and lower in the Kwando River, most likely in response to the varying flood magnitudes. Total mortality rates, estimated using Hoenig’s maximum-age based equation, were high in the Zambezi River as a result of the high fishing pressure on this river. Overall floodplain fish ecology in the Zambezi, Kavango and Kwando rivers was influenced by the flood pulse, as was predicted by the flood pulse concept. Periodic and equilibrium life history strategists were found to adapt either to the pulsing environments of the Zambezi and Kavango rivers, or to the more stable environment of the Kwando River, and large bodied, long lived periodic strategists such as C. gariepinus tended to be highly plastic and able to thrive in most conditions. Data also suggested that Zambezi River food web structure and fish mortality rates have been impacted by overfishing, for which more information is needed to conserve and manage this system. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2018
- Full Text:
- Date Issued: 2017
- Authors: Taylor, Geraldine Claire
- Date: 2017
- Subjects: Fishes Ecology Zambia Zambezi District , Floodplain ecology Zambia Zambezi District , Stable isotopes , Fishes Food Zambia Zambezi District , Fishes Mortality Zambia Zambezi District , Fish populations Zambia Zambezi District , Fishes Growth
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/65055 , vital:28660 , DOI https://doi.org/10.21504/10962/65055
- Description: The Upper Zambezi, Kavango and Kwando rivers are three periodically interlinked floodplain rivers which share the same Upper Zambezian floodplain ichthyofauna. The aim of this thesis was to compare the biology and ecology of the fish communities in these three rivers. The objective was to test the hypothesis that fish community composition and assemblage structure, fish diets, food web structure and trophic dynamics, fish growth rates and total mortality are influenced by the differing flood magnitudes of the three rivers, in support of the flood pulse concept. To understand the abiotic characteristics of each river, water temperature, flood regime, total dissolved inorganic nitrogen concentrations and water quality parameters were measured and compared between rivers. Water temperatures varied seasonally, and seven day moving averages peaked above 30 °C in January, and fell to between 16 and 19 °C in June. The Zambezi River had the largest flood (6.14 m), followed by the Kavango River (3.80 m), while the Kwando River had the smallest flood (0.65 m). Total dissolved inorganic nitrogen concentrations were low in the Kavango and Zambezi Rivers (0.2 - 0.6 mg/l), and slightly higher in the Kwando River (<1 mg/l). Conductivity, total dissolved solids and total dissolved inorganic nitrogen concentrations decreased with the flood (dilution effect). Using biomass catch per unit effort data from experimental gillnets, fish community composition and assemblage structure was described, and differed between rivers in all hydrological seasons. In the Zambezi and Kavango rivers, fish assemblages varied with hydrological season as a result of the homogenising influence of the flood pulse, while in the Kwando River fish assemblages did not differ seasonally as flood pulses were small and often irregular. Differences in community composition were attributed to the abundance of Hydrocynus vittatus, a large bodied open water predator, in the Zambezi and Kavango rivers, and its relative absence in the Kwando River. Based on the results of the community composition, six focus species were chosen that were abundant and representative of the various feeding modes and life history strategies of the fish community. These were the striped robber Brycinus lateralis, sharptooth catfish Clarias gariepinus, blunttooth catfish Clarias ngamensis, African pike Hepsetus cuvieri, silver catfish Schilbe intermedius and purpleface largemouth Serranochromis macrocephalus. Stomach contents analysis was then used to compare the feeding ecology of the six example species between rivers. Clarias gariepinus, C. ngamensis and S. intermedius were piscivorous in the Zambezi and Kavango rivers, and preyed upon more invertebrates in the Kwando River, while Hepsetus cuvieri and S. macrocephalus were piscivorous in all three rivers. Differences in diets were attributed to seasonal prey abundance, with prey fishes abundant during falling and low water when the Zambezi and Kavango rivers were sampled, while invertebrates were abundant during rising and high water when the Kwando River was sampled. Prey mastication by B. lateralis made prey identification difficult. For other predators, the usefulness of stomach contents analysis for dietary descriptions was restricted by the high proportion of empty stomachs. As a result, whole ecosystem stable isotope analysis was used to gain a holistic understanding of the food web structure and fish feeding ecology of the three rivers. The Zambezi and Kavango river food webs were supported by C enriched resources such as C4 and C3 riparian vegetation from the floodplain, while the Kwando River food web was based on C depleted resources such as filamentous algae and aquatic macrophytes. The Zambezi River food web had a restricted nitrogen range, with reduced food chain length and the predators in this river did not occupy such elevated trophic positions compared to in the Kavango and Kwando river food webs. This was attributed to the overfishing of the primary and tertiary consumers in the Zambezi River, a phenomenon known to reduce food chain length. Focussing on predator communities, in the Zambezi and Kavango rivers, H. vittatus isotopic niche width was large and overlapped significantly with most other predators, while in the Kwando River predator niches were more distinct. This supported previously proposed hypotheses by describing H. vittatus as a dominant predator which excludes all other fishes by predation or competition. Despite the dominance of H. vittatus, C. gariepinus occupied the position of top predator in all three rivers, and information on the habitat use, feeding habits and trophic niches of the serranochromine cichlids added understanding of their ecology. Lastly, age was determined using sectioned sagittal otoliths for C. gariepinus, C. ngamensis, S. intermedius and S. macrocephalus and using whole asteriscus otoliths for B. lateralis and H. cuvieri, and growth was modelled using the von Bertalanffy growth equation. Growth performance was high in the Zambezi and Kavango rivers, and lower in the Kwando River, most likely in response to the varying flood magnitudes. Total mortality rates, estimated using Hoenig’s maximum-age based equation, were high in the Zambezi River as a result of the high fishing pressure on this river. Overall floodplain fish ecology in the Zambezi, Kavango and Kwando rivers was influenced by the flood pulse, as was predicted by the flood pulse concept. Periodic and equilibrium life history strategists were found to adapt either to the pulsing environments of the Zambezi and Kavango rivers, or to the more stable environment of the Kwando River, and large bodied, long lived periodic strategists such as C. gariepinus tended to be highly plastic and able to thrive in most conditions. Data also suggested that Zambezi River food web structure and fish mortality rates have been impacted by overfishing, for which more information is needed to conserve and manage this system. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2018
- Full Text:
- Date Issued: 2017
The role of protected areas in the conservation and management of fisheries in the Chobe District of Botswana
- Authors: Bakane, Modiegi
- Date: 2017
- Subjects: Cichlids Botswana Chobe District , Protected areas Botswana Chobe District , Fishery management Botswana Chobe District
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7459 , vital:21262
- Description: This study was aimed at better understanding the function of protected areas as a management strategy for the Chobe District fishery in Botswana, by first investigating the relative abundance in fish communities in and outside protected areas and secondly, by performing an assessment of the biology of commercially important large cichlid species viz threespot tilapia Oreochromis andersonii, greenhead tilapia Oreochromis macrochir and redbreast tilapia Coptodon rendalli. In this study, data and specimens were collected during seasonal surveys between September 2014 and April 2015, using the standard graded fleets of gillnets employed in other programmes in the region, together with D-nets, angling and electro-fishing. The study demonstrated that fish communities in the floodplain ecosystems in the Chobe District of Botswana were representative of the region, containing some 70 species in 14 families. This study also demonstrated that for all the species collected, the mean Catch Per Unit Effort (CPUE) by weight for all the species was significantly higher in protected areas (Kruskal Wallis Test; P<0.05) namely, Zibadianja Lagoon (38 ± 31 kg/net.night"1 and Savuti River/marsh 25 ± 19 kg/net.night"1) than in the fished Chobe River floodplains CPUE (6 ± 3 kg/net.night-1). Biological contributions were estimates of longevity, growth and maturity for O. andersonii, O. macrochir and C. rendalli. Age and growth were estimated using sectioned sagittal otoliths. The Von Bertalanffy growth equation from otolith derived length at age was Lt(mm) =298 (1-e-0 59(t=- 098)) for O. andersonii and Lt(mm) = 337 (1-e-0'20(t=-235)) for C. rendalli. The results indicated that protected areas enhanced fish longevity, and fish in protected areas were larger and older than those in exploited areas. Maturity estimates for the large cichlids were consistent with other research in the region and the length-at-50% maturity was estimated as 250mm Lt for O. andersonii, 225 mm Lt for O. macrochir and 210 mm Lt for C. rendalli. Management recommendations are therefore to retain gill net mesh size regulations that ensure that these fish reach maturity and can breed before being harvested and to assess the possibility of increasing the number of protected areas in the district.
- Full Text:
- Date Issued: 2017
- Authors: Bakane, Modiegi
- Date: 2017
- Subjects: Cichlids Botswana Chobe District , Protected areas Botswana Chobe District , Fishery management Botswana Chobe District
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7459 , vital:21262
- Description: This study was aimed at better understanding the function of protected areas as a management strategy for the Chobe District fishery in Botswana, by first investigating the relative abundance in fish communities in and outside protected areas and secondly, by performing an assessment of the biology of commercially important large cichlid species viz threespot tilapia Oreochromis andersonii, greenhead tilapia Oreochromis macrochir and redbreast tilapia Coptodon rendalli. In this study, data and specimens were collected during seasonal surveys between September 2014 and April 2015, using the standard graded fleets of gillnets employed in other programmes in the region, together with D-nets, angling and electro-fishing. The study demonstrated that fish communities in the floodplain ecosystems in the Chobe District of Botswana were representative of the region, containing some 70 species in 14 families. This study also demonstrated that for all the species collected, the mean Catch Per Unit Effort (CPUE) by weight for all the species was significantly higher in protected areas (Kruskal Wallis Test; P<0.05) namely, Zibadianja Lagoon (38 ± 31 kg/net.night"1 and Savuti River/marsh 25 ± 19 kg/net.night"1) than in the fished Chobe River floodplains CPUE (6 ± 3 kg/net.night-1). Biological contributions were estimates of longevity, growth and maturity for O. andersonii, O. macrochir and C. rendalli. Age and growth were estimated using sectioned sagittal otoliths. The Von Bertalanffy growth equation from otolith derived length at age was Lt(mm) =298 (1-e-0 59(t=- 098)) for O. andersonii and Lt(mm) = 337 (1-e-0'20(t=-235)) for C. rendalli. The results indicated that protected areas enhanced fish longevity, and fish in protected areas were larger and older than those in exploited areas. Maturity estimates for the large cichlids were consistent with other research in the region and the length-at-50% maturity was estimated as 250mm Lt for O. andersonii, 225 mm Lt for O. macrochir and 210 mm Lt for C. rendalli. Management recommendations are therefore to retain gill net mesh size regulations that ensure that these fish reach maturity and can breed before being harvested and to assess the possibility of increasing the number of protected areas in the district.
- Full Text:
- Date Issued: 2017
Biology and ecology of Glossogobius callidus (Smith 1937) in irrigation impoundments in the Sundays River Valley of the Eastern Cape
- Authors: Mofu, Lubabalo
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/1136 , vital:20023
- Description: The River Goby Glossogobius callidus (Smith, 1937) is a native abundant fish in both freshwater and estuarine habitats in the Cape Fold Ecoregion, yet little information is available on its life-history. This study aims to contribute to knowledge on the age and growth, reproductive biology and the diet and feeding habits of G. callidus in irrigation impoundments. Glossogobius callidus was sampled monthly from August 2013 till March 2015; from the irrigation ponds in the Sundays River Valley, Eastern Cape Province, South Africa. To determine sex, gonads were visually assessed under a dissecting microscope to confirm the sex based on the shape of the urogenital papillae. Fish were then dissected to confirm sex and gonads were categorised into five macroscopic stages which were histologically validated. Microscopic stages of gonadal development were discerned based on nuclear and cytoplasmic characteristics of the oocyte or sperm. Ovaries and sperms were assigned stages based on the most advanced type of oocyte present. In total 2054 fishes ranging in length from 21.1 mm to 137.2 mm TL were sampled. The sex ratio (1.1 males: 1 females) did not differ from unity (x2 = 0.027, df = 1, p = 0.87). Length at 50% maturity (Lm) was 70 mm TL females and 72 mm TL for males. Spawning season was mid-spring and mid-summer and mean ± S.D absolute fecundity was estimated at 1028.2 ± 131.7 ova/fish. Relative fecundity (number of vitellogenic oocytes per gram of eviscerated fish mass) were estimated at 50 ± 18 ova/fish gram. Otoliths from 560 fish were used for ageing. Growth zone deposition rate was validated using edge analysis. As a unimodal periodic regression model best described the temporal proportion of opaque zone deposition on the edge of otoliths over a one-year period, growth zone deposition rate was validated as annual. The oldest female fish was a 4-year old 84.4 mm TL fish and the oldest male was a 7-year old 100.5 mm TL fish. The length-at-age for the entire population of 560 G. callidus provided von Bertalanffy parameters of Lt = 92 (1 - e -0.58(t + 0.4)) mm TL for the entire population, Lt = 70 (1 - e -1.8 (t + 0.06)) mm TL for males and Lt = 65 (1 - e -1.8 (t + 0.05)) mm TL for females. Converting length at maturity to age at maturity demonstrated that G. callidus attained maturity at an age of 2-years. Growth performance described using the phi-prime index showed that G. callidus had lower growth performance compared to the invasive Neogobius melanostomus. Using age structure, natural mortality was estimated at 1.31 yr-1 using catch curve analysis. Diet of G. callidus comprised of ten taxonomic groups. Among these, aquatic invertebrates were the most diverse group but while relative contribution of the dietary components varied across all size classes and seasons, the key prey items were consistently found in all size classes. These were Diptera, Hemiptera, Trichoptera, Odonata, Cladocera, Copepoda, Hydracarina, Amphipoda, Crustacea, and Mollusca. While dietary differences were observed between the size classes and throughout the seasons, G. callidus can be regarded as a generalist feeder preying on an array of different species. Given its abundance and diet, I suggest that G. callidus contribute considerably to the invertebrate predation pressure in these artificial aquatic environments in an arid region. In summary, medium fecundity, fast growth, moderate maturity, and a generalist feeding behaviour demonstrate that G. callidus is an equilibrium life strategist. In comparison with other species, the life-history traits of G. callidus from irrigation impoundments resemble those of other freshwater goby species, some of which are global invaders.
- Full Text:
- Date Issued: 2016
- Authors: Mofu, Lubabalo
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/1136 , vital:20023
- Description: The River Goby Glossogobius callidus (Smith, 1937) is a native abundant fish in both freshwater and estuarine habitats in the Cape Fold Ecoregion, yet little information is available on its life-history. This study aims to contribute to knowledge on the age and growth, reproductive biology and the diet and feeding habits of G. callidus in irrigation impoundments. Glossogobius callidus was sampled monthly from August 2013 till March 2015; from the irrigation ponds in the Sundays River Valley, Eastern Cape Province, South Africa. To determine sex, gonads were visually assessed under a dissecting microscope to confirm the sex based on the shape of the urogenital papillae. Fish were then dissected to confirm sex and gonads were categorised into five macroscopic stages which were histologically validated. Microscopic stages of gonadal development were discerned based on nuclear and cytoplasmic characteristics of the oocyte or sperm. Ovaries and sperms were assigned stages based on the most advanced type of oocyte present. In total 2054 fishes ranging in length from 21.1 mm to 137.2 mm TL were sampled. The sex ratio (1.1 males: 1 females) did not differ from unity (x2 = 0.027, df = 1, p = 0.87). Length at 50% maturity (Lm) was 70 mm TL females and 72 mm TL for males. Spawning season was mid-spring and mid-summer and mean ± S.D absolute fecundity was estimated at 1028.2 ± 131.7 ova/fish. Relative fecundity (number of vitellogenic oocytes per gram of eviscerated fish mass) were estimated at 50 ± 18 ova/fish gram. Otoliths from 560 fish were used for ageing. Growth zone deposition rate was validated using edge analysis. As a unimodal periodic regression model best described the temporal proportion of opaque zone deposition on the edge of otoliths over a one-year period, growth zone deposition rate was validated as annual. The oldest female fish was a 4-year old 84.4 mm TL fish and the oldest male was a 7-year old 100.5 mm TL fish. The length-at-age for the entire population of 560 G. callidus provided von Bertalanffy parameters of Lt = 92 (1 - e -0.58(t + 0.4)) mm TL for the entire population, Lt = 70 (1 - e -1.8 (t + 0.06)) mm TL for males and Lt = 65 (1 - e -1.8 (t + 0.05)) mm TL for females. Converting length at maturity to age at maturity demonstrated that G. callidus attained maturity at an age of 2-years. Growth performance described using the phi-prime index showed that G. callidus had lower growth performance compared to the invasive Neogobius melanostomus. Using age structure, natural mortality was estimated at 1.31 yr-1 using catch curve analysis. Diet of G. callidus comprised of ten taxonomic groups. Among these, aquatic invertebrates were the most diverse group but while relative contribution of the dietary components varied across all size classes and seasons, the key prey items were consistently found in all size classes. These were Diptera, Hemiptera, Trichoptera, Odonata, Cladocera, Copepoda, Hydracarina, Amphipoda, Crustacea, and Mollusca. While dietary differences were observed between the size classes and throughout the seasons, G. callidus can be regarded as a generalist feeder preying on an array of different species. Given its abundance and diet, I suggest that G. callidus contribute considerably to the invertebrate predation pressure in these artificial aquatic environments in an arid region. In summary, medium fecundity, fast growth, moderate maturity, and a generalist feeding behaviour demonstrate that G. callidus is an equilibrium life strategist. In comparison with other species, the life-history traits of G. callidus from irrigation impoundments resemble those of other freshwater goby species, some of which are global invaders.
- Full Text:
- Date Issued: 2016
Assessment of the Lake Liambezi fishery, Zambezi region, Namibia
- Authors: Simasiku, Evans Kamwi
- Date: 2014
- Subjects: Fishery management -- Namibia -- Lake Liambezi , Seines -- Namibia -- Lake Liambezi , Gillnetting -- Namibia -- Lake Liambezi , Fishes -- Namibia -- Lake Liambezi , Fisheries -- Catch effort -- Namibia -- Lake Liambezi
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5366 , http://hdl.handle.net/10962/d1013036
- Description: Lake Liambezi in the Zambezi Region of Namibia, formerly known as the Caprivi Region, is shallow (<6m deep) and characterised by cyclic episodes of filling and drying. When full the lake supports a highly productive fishery and when dry the lake is completely dry and used for agriculture and grazing. In 2000 the lake filled, and between May 2011 and April 2012 was surveyed using beach seine, experimental gillnets and catch landing surveys to obtain information for conservation and management recommendations for the fishery. Littoral fishes in Lake Liambezi and the Kavango floodplain were sampled using seine net and physicochemical properties were measured. Seine net surveys demonstrated that Lake Liambezi littoral zones were dominated by fishes of the family Alestidae (59.7%) while Cichlids constituted the most diverse family. Juvenile Tilapia rendalli and Oreochromis macrochir were among the five most important species in the littoral zone, indicating that these commercially important species use the littoral zone as a nursery ground. Since T. rendalli and O. macrochir are commercially important species, because of this, it is advised that seine nets should not be used. Catch efficiency between monofilament and multifilament gillnets in Lake Liambezi offshore waters were assessed. Catch efficiency experimental fishing trials showed that monofilament gillnets catch per unit effort (CPUE) was three times higher than that of multifilament gillnets for Oreochromis andersonii, O. macrochir, T. rendalli, Serranochromis macrocephalus and Clarias spp. Oreochromis andersonii comprised over 66% of the overall CPUE for both net types combined indicating the importance of this species in the gillnet fishery on the lake. A fishery has been established on the lake with more than 300 canoes and 120 fishermen using monofilament and multifilament gillnets. CPUE was 15 kg/canoe/day and was significantly (P < 0.05) associated with monthly temperature and moon phase parameters indicating that the fishery of Lake Liambezi may be altered by climate and environmental factors. Annual catch from Lake Liambezi was estimated at 3193t with an estimated productivity of 106kg/ha, suggesting that Lake Liambezi makes a significant contribution to the fish supply in the Zambezi Region. Recommendations were made to manage the Lake Liambezi fishery by imposing restrictions on effort (number of fishing boats), gear type, mesh sizes and access. Proper fisheries management and monitoring should incorporate climatic and environmental factors such as temperature and moon phase to meet the challenges of global climatic changes as well as other environmental issues.
- Full Text:
- Date Issued: 2014
- Authors: Simasiku, Evans Kamwi
- Date: 2014
- Subjects: Fishery management -- Namibia -- Lake Liambezi , Seines -- Namibia -- Lake Liambezi , Gillnetting -- Namibia -- Lake Liambezi , Fishes -- Namibia -- Lake Liambezi , Fisheries -- Catch effort -- Namibia -- Lake Liambezi
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5366 , http://hdl.handle.net/10962/d1013036
- Description: Lake Liambezi in the Zambezi Region of Namibia, formerly known as the Caprivi Region, is shallow (<6m deep) and characterised by cyclic episodes of filling and drying. When full the lake supports a highly productive fishery and when dry the lake is completely dry and used for agriculture and grazing. In 2000 the lake filled, and between May 2011 and April 2012 was surveyed using beach seine, experimental gillnets and catch landing surveys to obtain information for conservation and management recommendations for the fishery. Littoral fishes in Lake Liambezi and the Kavango floodplain were sampled using seine net and physicochemical properties were measured. Seine net surveys demonstrated that Lake Liambezi littoral zones were dominated by fishes of the family Alestidae (59.7%) while Cichlids constituted the most diverse family. Juvenile Tilapia rendalli and Oreochromis macrochir were among the five most important species in the littoral zone, indicating that these commercially important species use the littoral zone as a nursery ground. Since T. rendalli and O. macrochir are commercially important species, because of this, it is advised that seine nets should not be used. Catch efficiency between monofilament and multifilament gillnets in Lake Liambezi offshore waters were assessed. Catch efficiency experimental fishing trials showed that monofilament gillnets catch per unit effort (CPUE) was three times higher than that of multifilament gillnets for Oreochromis andersonii, O. macrochir, T. rendalli, Serranochromis macrocephalus and Clarias spp. Oreochromis andersonii comprised over 66% of the overall CPUE for both net types combined indicating the importance of this species in the gillnet fishery on the lake. A fishery has been established on the lake with more than 300 canoes and 120 fishermen using monofilament and multifilament gillnets. CPUE was 15 kg/canoe/day and was significantly (P < 0.05) associated with monthly temperature and moon phase parameters indicating that the fishery of Lake Liambezi may be altered by climate and environmental factors. Annual catch from Lake Liambezi was estimated at 3193t with an estimated productivity of 106kg/ha, suggesting that Lake Liambezi makes a significant contribution to the fish supply in the Zambezi Region. Recommendations were made to manage the Lake Liambezi fishery by imposing restrictions on effort (number of fishing boats), gear type, mesh sizes and access. Proper fisheries management and monitoring should incorporate climatic and environmental factors such as temperature and moon phase to meet the challenges of global climatic changes as well as other environmental issues.
- Full Text:
- Date Issued: 2014
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
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