Towards a norm of compliance in recreational fisheries
- Authors: Bova, Christopher S
- Date: 2019
- Subjects: Fishing -- Management -- South Africa , Fishery law and legislation -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/95909 , vital:31213
- Description: The activity of fishing can be traced back to prehistoric times. However, only in the last century has there been a focus on the management of fisheries. Fishery regulations are tools used by resource managers with the aim of protecting the long-term sustainability of fishery resources. Although there is an overwhelming amount of evidence demonstrating the decline of fisheries, non-compliance with these regulations by fishers continues to manifest, which can exacerbate the negative ecological impacts of fisheries. Popular methods towards the measurement of noncompliance in fisheries derived from previous human dimensions literature may be flawed. Theories on improving compliance behaviour have typically relied on theory, which has at times proved paradoxical. Addressing the issues of non-compliance within a fishery of interest requires measuring the levels of non-compliance within the fishery and determining the relevant sociopsychological drivers behind the non-compliant behaviour. The data collection methods used during these assessments are limited in human dimensions research and are often case and context specific, requiring researchers to identify which approach is most practical for the specific fishery of interest. By identifying relevant behavioural drivers of non-compliance, a more effective approach aimed at improving compliance can be tailored. The recreational marine-based shore fishery (MBSF) in South Africa is not impervious to noncomplaint behaviour. In fact, it has been estimated to have relatively high rates of non-compliance. This high level of non-compliance makes the South African MBSF a unique and optimal context in which to undertake research that aims to formulate a framework towards compliance assessments and that develops a suitable approach for improving compliance rates. Using surveys to obtain compliance data can provide a range of details about violators, however they are susceptible to social desirability bias (SDB). Choosing the best method for controlling SDB required an assessment of existing methods for doing so. In this first part of the study, only fishers who were covertly observed breaking the rules were surveyed, using one of three methods for reducing SDB, to ground-truth the responses. Ground-truthing was done to determine which method would be most effective for a large-scale study within the same fishery. Of the methods used, which include the direct questioning method (DQM), the random response technique (RRT) and the ballot box method (BBM), all contained some level of SDB. However, the BBM provided a significantly higher level of response accuracy (79.6% ± 11.9) than the DQM (46.5% ± 14.9) and the RRT (44.3% ± 12.5). Random-stratified roving creel compliance surveys that employed the BBM were then undertaken at various locations along South Africa’s coastline to estimate current rates of non-compliance, and the face-to-face results were compared to results from an identical online survey to determine the suitability of online surveys as a replacement. The results indicated that online surveys only represent a subgroup of the fisher population within the MBSF, suggesting that face-to-face survey methods are required to obtain a more comprehensive sample and a more robust estimate of noncompliance. The results, based on 453 face-to-face surveys, showed a high level of overall self-reported noncompliance (48.3%) within the fishery. Responses to Likert scale survey questions on various aspects of the fishery, including angler motivations for fishing, were then modelled to test the relationship between the anglers’ responses and their compliance behaviour. In the South African MBSF context, the most significant behavioural drivers behind non-compliance related to normative concepts. Specifically, the poor perceptions of management and value-based legitimacy as well as low levels of moral obligation to adhere to the regulations appeared to contribute most to the observed non-compliant behaviour. Angler motivations for fishing also played a significant role in determining the compliance behaviour of anglers, with those fishing for food being more likely to violate regulations. In most countries, regardless of economic context, interventions to improve recreational fishery compliance have been developed around the instrumental concept. However, these findings suggest that for recreational fisheries, managers would do well to evaluate the impact of normative concepts on compliance and to design interventions aimed at addressing these. In the case of the South African MBSF, interventions that address angler perceptions of legitimacy and aim to correct misperceptions about social norms of compliance may provide a more practical and cost- effective method for improving poor compliance behaviour.
- Full Text:
- Date Issued: 2019
- Authors: Bova, Christopher S
- Date: 2019
- Subjects: Fishing -- Management -- South Africa , Fishery law and legislation -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/95909 , vital:31213
- Description: The activity of fishing can be traced back to prehistoric times. However, only in the last century has there been a focus on the management of fisheries. Fishery regulations are tools used by resource managers with the aim of protecting the long-term sustainability of fishery resources. Although there is an overwhelming amount of evidence demonstrating the decline of fisheries, non-compliance with these regulations by fishers continues to manifest, which can exacerbate the negative ecological impacts of fisheries. Popular methods towards the measurement of noncompliance in fisheries derived from previous human dimensions literature may be flawed. Theories on improving compliance behaviour have typically relied on theory, which has at times proved paradoxical. Addressing the issues of non-compliance within a fishery of interest requires measuring the levels of non-compliance within the fishery and determining the relevant sociopsychological drivers behind the non-compliant behaviour. The data collection methods used during these assessments are limited in human dimensions research and are often case and context specific, requiring researchers to identify which approach is most practical for the specific fishery of interest. By identifying relevant behavioural drivers of non-compliance, a more effective approach aimed at improving compliance can be tailored. The recreational marine-based shore fishery (MBSF) in South Africa is not impervious to noncomplaint behaviour. In fact, it has been estimated to have relatively high rates of non-compliance. This high level of non-compliance makes the South African MBSF a unique and optimal context in which to undertake research that aims to formulate a framework towards compliance assessments and that develops a suitable approach for improving compliance rates. Using surveys to obtain compliance data can provide a range of details about violators, however they are susceptible to social desirability bias (SDB). Choosing the best method for controlling SDB required an assessment of existing methods for doing so. In this first part of the study, only fishers who were covertly observed breaking the rules were surveyed, using one of three methods for reducing SDB, to ground-truth the responses. Ground-truthing was done to determine which method would be most effective for a large-scale study within the same fishery. Of the methods used, which include the direct questioning method (DQM), the random response technique (RRT) and the ballot box method (BBM), all contained some level of SDB. However, the BBM provided a significantly higher level of response accuracy (79.6% ± 11.9) than the DQM (46.5% ± 14.9) and the RRT (44.3% ± 12.5). Random-stratified roving creel compliance surveys that employed the BBM were then undertaken at various locations along South Africa’s coastline to estimate current rates of non-compliance, and the face-to-face results were compared to results from an identical online survey to determine the suitability of online surveys as a replacement. The results indicated that online surveys only represent a subgroup of the fisher population within the MBSF, suggesting that face-to-face survey methods are required to obtain a more comprehensive sample and a more robust estimate of noncompliance. The results, based on 453 face-to-face surveys, showed a high level of overall self-reported noncompliance (48.3%) within the fishery. Responses to Likert scale survey questions on various aspects of the fishery, including angler motivations for fishing, were then modelled to test the relationship between the anglers’ responses and their compliance behaviour. In the South African MBSF context, the most significant behavioural drivers behind non-compliance related to normative concepts. Specifically, the poor perceptions of management and value-based legitimacy as well as low levels of moral obligation to adhere to the regulations appeared to contribute most to the observed non-compliant behaviour. Angler motivations for fishing also played a significant role in determining the compliance behaviour of anglers, with those fishing for food being more likely to violate regulations. In most countries, regardless of economic context, interventions to improve recreational fishery compliance have been developed around the instrumental concept. However, these findings suggest that for recreational fisheries, managers would do well to evaluate the impact of normative concepts on compliance and to design interventions aimed at addressing these. In the case of the South African MBSF, interventions that address angler perceptions of legitimacy and aim to correct misperceptions about social norms of compliance may provide a more practical and cost- effective method for improving poor compliance behaviour.
- Full Text:
- Date Issued: 2019
Towards defining the tipping point of tolerance to CO2-induced ocean acidification for the growth, development and metabolism of larval dusky kob Argyrosomus japonicus (Pisces: Sciaenidae)
- Authors: Mpopetsi, Pule Peter
- Date: 2019
- Subjects: Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Larvae , Argyrosomus -- Larvae -- Effect of water acidification on , Argyrosomus japonicus -- Larvae -- Nutrition , Argyrosomus -- Larvae -- Nutrition , Ocean acidification
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/71602 , vital:29924
- Description: Increased CO2 production and the consequent ocean acidification (OA) have been identified as one of the greatest threats to both calcifying and non-calcifying marine organisms. Traditionally, marine fishes, as non-calcifying organisms, were considered to have a higher tolerance to near-future OA conditions owing to their well-developed ion regulatory mechanisms. However, recent studies provide evidence to suggest that they may not be as resilient to near-future OA conditions as previously thought. In addition, earlier life stages of marine fishes are thought to be less tolerant than juveniles and adults of the same species as they lack well-developed ion regulatory mechanisms for maintaining homeostasis. This study follows up on previous studies examining the effects of near-future OA on larval Argyrosomus japonicus, an estuarine-dependent marine fish species, in order to identify the tipping point of tolerance for the larvae of this species. These previous studies showed that elevated pCO2, predicted for the year 2100, had negative effects on growth, development and metabolism and ultimately, survival of larval A. japonicus from post-flexion stage. Larval A. japonicus in the present study were reared from egg up to 22 DAH (days after hatching) under three treatments. The three treatments, (pCO2 353 μatm; pH 8.03), (pCO2 451 μatm; pH 7.93) and (pCO2 602 μatm; pH 7.83) corresponded to levels predicted to occur in year 2050, 2068 and 2090 respectively under the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (IPCC RCP) 8.5 model. Size-at-hatch, growth, development and metabolic responses (standard and active metabolic rates and metabolic scope) were assessed and compared between the three treatments throughout the rearing period. Five earlier larval life stages (hatchling – flexion/post-flexion) were identified by the end of the experiment. There were no significant differences in size-at-hatch (P > 0.05), development or the active metabolic (P > 0.05) or metabolic scope (P > 0.05) of fish in the three treatments throughout the study. However, the standard metabolic rate was significantly higher in the year 2068 treatment but only at the flexion/post-flexion stage which could be attributed to differences in developmental rates (including the development of the gills) between the 2068 and the other two treatments. Overall, the metabolic scope was narrowest in the 2090 treatment, but varied according to life stage. Although not significantly different, metabolic scope in the 2090 treatment was noticeably lower at the flexion stage compared to the other two treatments, and the development appeared slower, suggesting that this could be the stage most prone to OA. The study concluded that, in isolation, OA levels predicted to occur between 2050 and 2090 will not negatively affect size-at-hatch, growth, development, and metabolic responses of larval A. japonicus up to 22 DAH (flexion/post-flexion stage). Taken together with the previous studies of the same species, the tipping point of tolerance (where negative impacts will begin) in larvae of the species appears to be between the years 2090 and 2100.
- Full Text:
- Date Issued: 2019
- Authors: Mpopetsi, Pule Peter
- Date: 2019
- Subjects: Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Larvae , Argyrosomus -- Larvae -- Effect of water acidification on , Argyrosomus japonicus -- Larvae -- Nutrition , Argyrosomus -- Larvae -- Nutrition , Ocean acidification
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/71602 , vital:29924
- Description: Increased CO2 production and the consequent ocean acidification (OA) have been identified as one of the greatest threats to both calcifying and non-calcifying marine organisms. Traditionally, marine fishes, as non-calcifying organisms, were considered to have a higher tolerance to near-future OA conditions owing to their well-developed ion regulatory mechanisms. However, recent studies provide evidence to suggest that they may not be as resilient to near-future OA conditions as previously thought. In addition, earlier life stages of marine fishes are thought to be less tolerant than juveniles and adults of the same species as they lack well-developed ion regulatory mechanisms for maintaining homeostasis. This study follows up on previous studies examining the effects of near-future OA on larval Argyrosomus japonicus, an estuarine-dependent marine fish species, in order to identify the tipping point of tolerance for the larvae of this species. These previous studies showed that elevated pCO2, predicted for the year 2100, had negative effects on growth, development and metabolism and ultimately, survival of larval A. japonicus from post-flexion stage. Larval A. japonicus in the present study were reared from egg up to 22 DAH (days after hatching) under three treatments. The three treatments, (pCO2 353 μatm; pH 8.03), (pCO2 451 μatm; pH 7.93) and (pCO2 602 μatm; pH 7.83) corresponded to levels predicted to occur in year 2050, 2068 and 2090 respectively under the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (IPCC RCP) 8.5 model. Size-at-hatch, growth, development and metabolic responses (standard and active metabolic rates and metabolic scope) were assessed and compared between the three treatments throughout the rearing period. Five earlier larval life stages (hatchling – flexion/post-flexion) were identified by the end of the experiment. There were no significant differences in size-at-hatch (P > 0.05), development or the active metabolic (P > 0.05) or metabolic scope (P > 0.05) of fish in the three treatments throughout the study. However, the standard metabolic rate was significantly higher in the year 2068 treatment but only at the flexion/post-flexion stage which could be attributed to differences in developmental rates (including the development of the gills) between the 2068 and the other two treatments. Overall, the metabolic scope was narrowest in the 2090 treatment, but varied according to life stage. Although not significantly different, metabolic scope in the 2090 treatment was noticeably lower at the flexion stage compared to the other two treatments, and the development appeared slower, suggesting that this could be the stage most prone to OA. The study concluded that, in isolation, OA levels predicted to occur between 2050 and 2090 will not negatively affect size-at-hatch, growth, development, and metabolic responses of larval A. japonicus up to 22 DAH (flexion/post-flexion stage). Taken together with the previous studies of the same species, the tipping point of tolerance (where negative impacts will begin) in larvae of the species appears to be between the years 2090 and 2100.
- Full Text:
- Date Issued: 2019
Using a multi-method approach to understand the movement patterns and the associated environmental correlates of an iconic West African recreational fish
- Authors: Winkler, Alexander Claus
- Date: 2019
- Subjects: Carangidae fishing , Carangidae -- Migration , Carangidae -- Namibia , Carangidae -- Angola , Fish tagging , Carangidae -- Benguela Current , Underwater acoustic telemetry , Ocean temperature -- Physiological effect , Fishes -- Effect of temperature on
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/76530 , vital:30597
- Description: The leerfish (Lichia amia), is a large, primarily coastal recreational fish species with a distribution extending from Portugal down the west coast of African to southern Mozambique. Owing to its large size (30 kg), strong fighting abilities and habit of taking surface artificial lures, this species has taken on an iconic stature among shore-based recreational anglers. Its reputation has made it an important angling tourism species that makes an important contribution to the economy of developing countries. For example, the species brought US$243 per harvested kilogramme into the local southern Angola economy. Despite its high value, little is known about its movement patterns in the northern Benguela coastal region, a region which includes southern Angola and northern Namibia. While much is known about the migratory patterns of the South African stock of L. amia, recent molecular studies have shown that the northern Benguela stock of L. amia has been isolated from the South African population for at least two million years, a consequence of the development of the cold Lüderitz upwelling cell in southern Namibia. Although the global population of L. amia is considered a single species, prominent biogeographic barriers within its distribution and subtle morphological differences between specimens captured within its tropical versus warm-temperate distribution suggest otherwise. A multi-method approach incorporating passive acoustic telemetry (PAT), recreational catch-per-unit-effort (CPUE) and conventional tagging (CT) in southern Angola, as well as recreational fisher-ecological knowledge (FEK) from Namibia, was used to investigate the large-scale movement patterns of L. amia within the northern Benguela coastal region. While each method had its own associated limitations, the combination provided a holistic picture of the population's seasonal migratory patterns. Furthermore, PAT successfully identified partial migration with 25% vs 75% of monitored fish exhibiting resident (movements < 100 km) or migratory (movements > 100 km) behaviour, respectively. Further behavioural diversity was observed with ‘resident’, ‘roaming’ and ‘embayment’ contingents identified based on varying levels of affinity to certain habitats. The presence of both resident and migratory individuals within the northernmost study during June and July, combined with available biological information, suggested that area-specific spawning may take place. While PAT, CPUE and CT largely aligned in determining area specific high-area use, results from network analyses and mixed effects models conducted on the PAT data supported the spawning hypothesis, with anomalous behaviour around specific receivers during the spawning season. All fish, regardless of behavioural contingent, displayed similar movement behaviour during the spawning season and this was driven by factors generally associated with reproduction, such as lunar illumination. Interestingly, these drivers were different from those that determined the area specific use of individuals outside of the spawning season. The environmental drivers of longshore migration into the northern study site were identified as a decline in water temperature and shorter day lengths. The results of this study highlight the importance of using a multi-method approach in determining migratory movement behaviour, area specific area use, and stock structure of key fisheries species. The identification of different behavioural contingents highlights the importance of acknowledging individual variation in movement and habitat-use patterns. This is particularly relevant as future climate change and spatiotemporal variation in fishing effort may artificially skew natural selection processes to favour certain behavioural groups. This study also highlighted the importance of scientists forming relationships with resource-users, such as recreational angling lodges in areas where limited research has been conducted. This is particularly relevant within the West African context where little is known about many of the fish species that are being increasingly targeted by tourism angling ventures.
- Full Text:
- Date Issued: 2019
- Authors: Winkler, Alexander Claus
- Date: 2019
- Subjects: Carangidae fishing , Carangidae -- Migration , Carangidae -- Namibia , Carangidae -- Angola , Fish tagging , Carangidae -- Benguela Current , Underwater acoustic telemetry , Ocean temperature -- Physiological effect , Fishes -- Effect of temperature on
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/76530 , vital:30597
- Description: The leerfish (Lichia amia), is a large, primarily coastal recreational fish species with a distribution extending from Portugal down the west coast of African to southern Mozambique. Owing to its large size (30 kg), strong fighting abilities and habit of taking surface artificial lures, this species has taken on an iconic stature among shore-based recreational anglers. Its reputation has made it an important angling tourism species that makes an important contribution to the economy of developing countries. For example, the species brought US$243 per harvested kilogramme into the local southern Angola economy. Despite its high value, little is known about its movement patterns in the northern Benguela coastal region, a region which includes southern Angola and northern Namibia. While much is known about the migratory patterns of the South African stock of L. amia, recent molecular studies have shown that the northern Benguela stock of L. amia has been isolated from the South African population for at least two million years, a consequence of the development of the cold Lüderitz upwelling cell in southern Namibia. Although the global population of L. amia is considered a single species, prominent biogeographic barriers within its distribution and subtle morphological differences between specimens captured within its tropical versus warm-temperate distribution suggest otherwise. A multi-method approach incorporating passive acoustic telemetry (PAT), recreational catch-per-unit-effort (CPUE) and conventional tagging (CT) in southern Angola, as well as recreational fisher-ecological knowledge (FEK) from Namibia, was used to investigate the large-scale movement patterns of L. amia within the northern Benguela coastal region. While each method had its own associated limitations, the combination provided a holistic picture of the population's seasonal migratory patterns. Furthermore, PAT successfully identified partial migration with 25% vs 75% of monitored fish exhibiting resident (movements < 100 km) or migratory (movements > 100 km) behaviour, respectively. Further behavioural diversity was observed with ‘resident’, ‘roaming’ and ‘embayment’ contingents identified based on varying levels of affinity to certain habitats. The presence of both resident and migratory individuals within the northernmost study during June and July, combined with available biological information, suggested that area-specific spawning may take place. While PAT, CPUE and CT largely aligned in determining area specific high-area use, results from network analyses and mixed effects models conducted on the PAT data supported the spawning hypothesis, with anomalous behaviour around specific receivers during the spawning season. All fish, regardless of behavioural contingent, displayed similar movement behaviour during the spawning season and this was driven by factors generally associated with reproduction, such as lunar illumination. Interestingly, these drivers were different from those that determined the area specific use of individuals outside of the spawning season. The environmental drivers of longshore migration into the northern study site were identified as a decline in water temperature and shorter day lengths. The results of this study highlight the importance of using a multi-method approach in determining migratory movement behaviour, area specific area use, and stock structure of key fisheries species. The identification of different behavioural contingents highlights the importance of acknowledging individual variation in movement and habitat-use patterns. This is particularly relevant as future climate change and spatiotemporal variation in fishing effort may artificially skew natural selection processes to favour certain behavioural groups. This study also highlighted the importance of scientists forming relationships with resource-users, such as recreational angling lodges in areas where limited research has been conducted. This is particularly relevant within the West African context where little is known about many of the fish species that are being increasingly targeted by tourism angling ventures.
- Full Text:
- Date Issued: 2019
Aspects of the nutritional physiology of the perlemoen Haliotis midae (L.) and red abalone H. rufescens (Swainson)
- Authors: Kemp, Justin Oliver Gordon
- Date: 2018
- Subjects: Haliotis midae , Haliotis midae fisheries , Red abalone , Haliotis midae -- Feeding and feeds , Red abalone -- Feeding and feeds , Haliotis midae -- Nutrition -- Requirements , Red abalone -- Nutrition -- Requirements , Haliotis midae -- Metabolism , Red abalone -- Metabolism , Haliotis midae -- Physiology , Red abalone -- Physiology , Stable isotopes , Algae as feed
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62314 , vital:28154
- Description: The source of abalone for human consumption has shown a dramatic shift away from wild-capture fisheries in the last 30 years, with over 90% of global production now coming from aquaculture. Farmers initially relied on the natural food of abalone (macroalgae) as a culture feed, though in regions where macroalgae availability was limiting, the need to develop formulated feeds was evident. Extensive research effort has led to the development of a number of formulated feed products currently employed in the industry. These feeds, however, differ markedly from the mixed macroalgal diets that abalone have evolved to utilise, particularly in terms of protein content and carbohydrate structure. The degree to which the nutritional physiology of abalone responds to these novel formulated diets, with and without macroalgal supplementation, was investigated in the current study. A multifaceted approach, combining growth trials, stable isotope nutrient tracers and metabolic experiments, was employed to gain insight into the post-absorption dynamics and utilisation of dietary nutrients under varying dietary regimes of fresh macroalgae and formulated feed. Growth trials conducted with both Haliotis rufescens and H. midae showed significantly higher growth and protein utilisation efficiency for abalone fed macroalgal diets compared to formulated feeds. Furthermore, when formulated feeds were supplemented with macroalgae to form combination diets, growth and the utilization of protein was improved compared to the formulated-feed-only diet. The poor utilisation of protein by H. midae fed the formulated feed could be traced, using a method combining stable isotope bio-markers with a Bayesian mixing model (SIAR), to the low incorporation of the fishmeal component of protein in the diet. The marked postprandial drop in the O:N ratio on abalone fed formulated feeds indicate that the protein was being diverted into catabolic metabolic pathways. The metabolic cost of digestion, termed specific dynamic action (SDA), was negated as a factor in the improved growth of abalone fed macroalgal diets, with the SDA coefficient 2.1 times that observed for formulated feed. Furthermore, the postprandial haemolymph glucose concentration (HGC) in H. midae was elevated when fed formulated feed compared to macroalgae. The high levels of circulating glucose are likely a result of the structure the carbohydrate source in formulated feeds and stimulate the deposition of glycogen through the allosteric control of glycogen synthase. Formulated feeds produced higher cooked meat yields in canning simulation trials, suggesting that muscle glycogen content may indirectly play a role in increasing canning yields through the displacement of collagen. The results of these empirical studies are synthesised under key themes, discussed within the context of their potential commercial relevance and future research directions are highlighted.
- Full Text:
- Date Issued: 2018
- Authors: Kemp, Justin Oliver Gordon
- Date: 2018
- Subjects: Haliotis midae , Haliotis midae fisheries , Red abalone , Haliotis midae -- Feeding and feeds , Red abalone -- Feeding and feeds , Haliotis midae -- Nutrition -- Requirements , Red abalone -- Nutrition -- Requirements , Haliotis midae -- Metabolism , Red abalone -- Metabolism , Haliotis midae -- Physiology , Red abalone -- Physiology , Stable isotopes , Algae as feed
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62314 , vital:28154
- Description: The source of abalone for human consumption has shown a dramatic shift away from wild-capture fisheries in the last 30 years, with over 90% of global production now coming from aquaculture. Farmers initially relied on the natural food of abalone (macroalgae) as a culture feed, though in regions where macroalgae availability was limiting, the need to develop formulated feeds was evident. Extensive research effort has led to the development of a number of formulated feed products currently employed in the industry. These feeds, however, differ markedly from the mixed macroalgal diets that abalone have evolved to utilise, particularly in terms of protein content and carbohydrate structure. The degree to which the nutritional physiology of abalone responds to these novel formulated diets, with and without macroalgal supplementation, was investigated in the current study. A multifaceted approach, combining growth trials, stable isotope nutrient tracers and metabolic experiments, was employed to gain insight into the post-absorption dynamics and utilisation of dietary nutrients under varying dietary regimes of fresh macroalgae and formulated feed. Growth trials conducted with both Haliotis rufescens and H. midae showed significantly higher growth and protein utilisation efficiency for abalone fed macroalgal diets compared to formulated feeds. Furthermore, when formulated feeds were supplemented with macroalgae to form combination diets, growth and the utilization of protein was improved compared to the formulated-feed-only diet. The poor utilisation of protein by H. midae fed the formulated feed could be traced, using a method combining stable isotope bio-markers with a Bayesian mixing model (SIAR), to the low incorporation of the fishmeal component of protein in the diet. The marked postprandial drop in the O:N ratio on abalone fed formulated feeds indicate that the protein was being diverted into catabolic metabolic pathways. The metabolic cost of digestion, termed specific dynamic action (SDA), was negated as a factor in the improved growth of abalone fed macroalgal diets, with the SDA coefficient 2.1 times that observed for formulated feed. Furthermore, the postprandial haemolymph glucose concentration (HGC) in H. midae was elevated when fed formulated feed compared to macroalgae. The high levels of circulating glucose are likely a result of the structure the carbohydrate source in formulated feeds and stimulate the deposition of glycogen through the allosteric control of glycogen synthase. Formulated feeds produced higher cooked meat yields in canning simulation trials, suggesting that muscle glycogen content may indirectly play a role in increasing canning yields through the displacement of collagen. The results of these empirical studies are synthesised under key themes, discussed within the context of their potential commercial relevance and future research directions are highlighted.
- Full Text:
- Date Issued: 2018
Effects of CO2-induced ocean acidification on the early development, growth, survival and skeletogenesis of the estuarine-dependant sciaenid Argyrosomus japonicus
- Authors: Erasmus, Bernard
- Date: 2018
- Subjects: Argyrosomus , Argyrosomus -- Growth , Argyrosomus -- Mortality , Argyrosomus -- Ecology , Argyrosomus -- Physiology , Ocean acidification , Marine ecology -- South Africa , Carbon dioxide -- Physiological effect
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60585 , vital:27799
- Description: Although it is increasingly accepted that ocean acidification poses a considerable threat to marine organisms, little is known about the likely response of fishes to this phenomenon. While initial research concluded that adult fishes may be tolerant to changes predicted in the next 300 years, the response of early life stages to end-of-century CO2 levels (~ 1100 µatm according to the IPCC RCP 8.5) remains unclear. To date, literature on the early growth and survival of fishes has yielded conflicting results, suggesting that vulnerability may be species dependant. The paucity of ocean acidification research on fishes is particularly evident when one considers larval skeletogenesis, with no robust studies on its impacts on bone and cartilage development. This study addresses the early life embryogenesis, hatching success, growth, skeletogenesis and survival of an estuarine-dependant species. Dusky kob (Argyrosomus japonicus) were reared in a control (pCO2 = 327.50 ± 80.07 qatm at pH 8.15), intermediate (pCO2 477.40 ± 59.46 qatm at pH 8.03) and high pCO2 treatment (pCO2 910.20 ± 136.45 qatm at pH 7.78) from egg to 29 days post-hatch (dph). Sixty individuals from each treatment were sacrificed at the egg stage and at 2, 6, 13, 18, 21 and 26 dph, measured and stained using an acid-free double- staining solution to prevent the deterioration of calcified matrices in fragile larval skeletons. The proportion of bone and cartilage was quantified at each stage using a novel pixel-counting method. Growth and skeletal development were identical between treatments until the onset of metamorphosis (21 dph). However, from the metamorphosis stage, the growth and skeletal development rate was significantly faster in the intermediate treatment and significantly slower in the high treatment when compared to the control treatment. By 26 dph, A. japonicus reared in high pCO2 were, on average, 47.2% smaller than the control treatment, and the relative proportion of bone in the body was 45.3% lower in the high pCO2 treatment when compared with the control. In addition, none of the fish in the high pCO2 treatment survived after 26 dph. It appears that the combination of the increased energy requirements during metamorphosis and the increased energy cost associated with acid-base regulation may account for reduced growth, skeletogenesis and poor survival in high pCO2. Regardless of the driver, the results of this study suggest that the pCO2 levels predicted for the end of the century may have negative effects on the growth, skeletal development, and survival during metamorphosis.
- Full Text:
- Date Issued: 2018
- Authors: Erasmus, Bernard
- Date: 2018
- Subjects: Argyrosomus , Argyrosomus -- Growth , Argyrosomus -- Mortality , Argyrosomus -- Ecology , Argyrosomus -- Physiology , Ocean acidification , Marine ecology -- South Africa , Carbon dioxide -- Physiological effect
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60585 , vital:27799
- Description: Although it is increasingly accepted that ocean acidification poses a considerable threat to marine organisms, little is known about the likely response of fishes to this phenomenon. While initial research concluded that adult fishes may be tolerant to changes predicted in the next 300 years, the response of early life stages to end-of-century CO2 levels (~ 1100 µatm according to the IPCC RCP 8.5) remains unclear. To date, literature on the early growth and survival of fishes has yielded conflicting results, suggesting that vulnerability may be species dependant. The paucity of ocean acidification research on fishes is particularly evident when one considers larval skeletogenesis, with no robust studies on its impacts on bone and cartilage development. This study addresses the early life embryogenesis, hatching success, growth, skeletogenesis and survival of an estuarine-dependant species. Dusky kob (Argyrosomus japonicus) were reared in a control (pCO2 = 327.50 ± 80.07 qatm at pH 8.15), intermediate (pCO2 477.40 ± 59.46 qatm at pH 8.03) and high pCO2 treatment (pCO2 910.20 ± 136.45 qatm at pH 7.78) from egg to 29 days post-hatch (dph). Sixty individuals from each treatment were sacrificed at the egg stage and at 2, 6, 13, 18, 21 and 26 dph, measured and stained using an acid-free double- staining solution to prevent the deterioration of calcified matrices in fragile larval skeletons. The proportion of bone and cartilage was quantified at each stage using a novel pixel-counting method. Growth and skeletal development were identical between treatments until the onset of metamorphosis (21 dph). However, from the metamorphosis stage, the growth and skeletal development rate was significantly faster in the intermediate treatment and significantly slower in the high treatment when compared to the control treatment. By 26 dph, A. japonicus reared in high pCO2 were, on average, 47.2% smaller than the control treatment, and the relative proportion of bone in the body was 45.3% lower in the high pCO2 treatment when compared with the control. In addition, none of the fish in the high pCO2 treatment survived after 26 dph. It appears that the combination of the increased energy requirements during metamorphosis and the increased energy cost associated with acid-base regulation may account for reduced growth, skeletogenesis and poor survival in high pCO2. Regardless of the driver, the results of this study suggest that the pCO2 levels predicted for the end of the century may have negative effects on the growth, skeletal development, and survival during metamorphosis.
- Full Text:
- Date Issued: 2018
Factors influencing estuarine and coastal connectivity of an estuarine-dependent fishery species, Pomadasys commersonnii (Haemulidae)
- Authors: Dames, Michael Henri
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62307 , vital:28153
- Description: Expected release date-April 2019
- Full Text:
- Date Issued: 2018
- Authors: Dames, Michael Henri
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62307 , vital:28153
- Description: Expected release date-April 2019
- Full Text:
- Date Issued: 2018
Morphological and genetic variation of Gymnothorax undulatus (Anguilliformes: Muraenidae) in the Western Indian Ocean
- Authors: Sithole, Yonela
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63722 , vital:28476
- Description: Expected release date-April 2019
- Full Text:
- Date Issued: 2018
- Authors: Sithole, Yonela
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63722 , vital:28476
- Description: Expected release date-April 2019
- Full Text:
- Date Issued: 2018
Movement of coastal fishery species in Southern Africa: research trends, characterisation of behaviours and a case study on fishery implications
- Authors: Maggs, Jade Quinton
- Date: 2018
- Subjects: Fishery management -- Africa, Southern , Fisheries -- Africa, Southern , Fisheries -- Catch effort , Fisheries -- Environmental aspects , Fisheries --Monitoring , Biotelemetry , Sustainable fisheries -- Africa, Southern , Overfishing -- Africa, Southern
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/60574 , vital:27798
- Description: Movement of fishes is an integral part of their daily life, but has significant implications for fishery management. As with nearly all coastal countries, South Africa relies on coastal fisheries as a renewable resource, but many stocks have been overexploited for decades. Although it has long been recognised that an understanding of fish movement is necessary for effective management, it is with some difficulty that the subject has been studied in the past. In recent years, however, improvements in technology have provided the means for more in-depth investigations into fish movement. This research has revealed a range of complex movement behaviours. Movement in fishes occurs on a variety of temporal and spatial scales leading to the characteristic patterns of distribution and abundance observed in marine ecosystems. Fishes move nearly constantly in search of food, shelter or reproductive opportunities. Observations of behaviours such as long-term site fidelity, longdistance migration and natal homing are enabling ecologists to understand patterns of distribution and abundance within a species' range. Fish movement around the South African coast has been studied on numerous occasions but this has largely been confined to studies on single species. Movement behaviour of multiple species has been studied, but this has been limited to spatially localised marine protected area research. There has been little attempt in southern Africa to synthesize interspecific movement behaviour over wide spatial scales.Unprecedented concern over the biological effects of overexploitation, together with rapid technological advances in biotelemetry, have provided the impetus for much research, on a global scale, into the movement of marine animals. I reviewed 101 marine and estuarine fish movement studies from southern Africa, published from 1928 to 2014, with the aim of synthesising research trends and findings. Trends showed an increasing emphasis on fish movement research in publications in the sub-tropical and warm-temperate biogeographic regions along the south and east coasts of southern Africa. Although 63% of publications featured only marine studies, research into fine-scale habitat use in estuaries has been on the increase, concomitant with increasing accessibility of biotelemetry. Overall, 26 fish families were identified in the surveyed literature with regionally endemic sparids featuring in 32% of the publications. Ten movement themes were identified in the surveyed literature, including broad-scale movement patterns, which featured in 68% of studies, followed by fine- scale habitat usage (33%) and protected areas (26%). The most prominent phenomenon, emerging from this research, is that of partial migration, which describes the occurrence of resident and migratory behaviour within a coexisting animal population. Substantial progress has also been made in unravelling the complexities of fine-scale movements in marine reserves and habitat usage in estuaries. While this knowledge has enabled more effective management of South Africa's multi-user, multi-species fisheries, focus should now be directed at improving our understanding of the commonalities in movement behaviour, the associated driving forces behind this behaviour and the extent of movement across reserve boundaries. Mark-recapture data, collected over the past 30 years by the Oceanographic Research Institute’s Cooperative Fish Tagging Project (ORICFTP), were used to investigate broad- scale movement patterns of 30 prominent coastal fishery species (Chapter 4). Fishes were tagged with plastic dart tags along the coastline of southern Africa from Angola to Mozambique. This exercise yielded more than 10000 recaptures. The 30 chosen species represented 14 families, although 12 species belonged to a single family (Sparidae). Overall, 67% of recaptures were reported from the original tagging locality and 73% were recorded within 5 km of the tagging locality. The remaining observations extended from 6-3000 km. Movements were assigned to four distance bins (0-5 km, 6-50km, 51-500km and >500 km) and modelled with an ordinal logistic regression. Species, life-stage (juvenile/adult) and time- at-liberty were included as predictor variables. Model coefficients were then included in a cluster analysis, which produced two primary groupings of species (Category I and II), with two sub-groupings (Category IIa and IIb). Category I species were characterised by wide-ranging movements, greatest median recapture length and highest trophic levels. Category II species were characterised by residency, lower median recapture length and lower trophic levels. These findings have implications for fisheries management. Exploitation of resident species may lead to localised depletion, but their diffuse spatial distribution may offer some resilience. In contrast, even localised targeting of migratory species may pose a population level risk if individuals are known to aggregate. Life-cycle diversity or intra-population variability describes the existence of alternative strategies or tactics among coexisting individuals within an animal population (Chapter 5). Partial migration is a specific case of life-cycle diversity where coexisting groups exhibit either resident or migratory (wide-ranging) behaviour within a single population. Mark- recapture data collected under the auspices of the ORICFTP were used to investigate the occurrence and nature of life-cycle diversity in the movement behaviour of five non- diadromous fish species around the coastline of southern Africa. Among the five species were three teleosts (Category I and IIa) and two elasmobranchs (Category I). A fish was considered to have remained resident if recaptured within 0-5 km after 365 days at liberty. A fish was considered to have undertaken a wide-ranging movement if recaptured more than 50 km away from the release site in 365 days or less. A total of 1848 individuals from the five study species were recaptured during the study, of which 73% of the observations were classified as being resident. Binomial logistic regression confirmed that species, life-stage (juvenile/adult) and ecoregion were significant (p < 0.001) predictors of the probability of wide-ranging behaviour. A Gaussian model confirmed that species and ecoregion were also significant (p < 0.001) predictors of direction and distance of wide-ranging movement. However, the direction and distance of wide-ranging movements in juveniles did not differ significantly (p > 0.05) to that of adults. The median growth rate was mostly greater in wide- ranging individuals; however, this was only statistically significant (p < 0.05) in two cases. These findings provide unequivocal evidence of life-cycle diversity in five fish species, with vastly different life-histories. This ecological phenomenon may provide species resilience at the population level and needs to be considered in fisheries management initiatives. The movement of fishes is a fundamental aspect to consider when designing fishery management regimes. Unfortunately, traditional management strategies have often disregarded movement behaviour to the detriment of fish populations (Chapter 6). As a case study, the management of Lichia amia (Category I: wide-ranging) was evaluated in the context of its movement behaviour. Long-term catch-per-unit-effort (CPUE) datasets were examined for three South African recreational fishery sectors. The CPUE was standardised using generalized linear models (delta-Gamma/hurdle approach) to reduce the effect of factors other than abundance. Factors that were available for this purpose were year, month and locality/zone. Year was included in every model as the primary objective was to detect trends in abundance over time. Although standardised CPUE for all sectors showed an overall long-term decline, there was considerable variability in trends between the different recreational sectors and between datasets. Contrasting trends between competitive shore angling and general shore angling datasets were ascribed to hyperstability in competitive CPUE data. Hyperstability in this case was mostly influenced by rapidly improving technology, techniques and communication networks amongst competitive anglers. Month and locality were significant factors explaining the probability of catching L. amia. This suggests that the predictable aggregatory behaviour of this species could further compound the observed CPUE hyperstability. Although the CPUE responded positively for six years after implementation of the first minimum size and bag limits, and for one year after the decommercialisation of the species, these regulations and their amendments failed to arrest a long-term decline in the CPUE despite the ample evidence for hyperstability. It is clear from this case study that the predictable nature of wide-ranging behaviour in L. amia has made the population vulnerable to exploitation. This has led to the demise in the population, which could have been worse if not for the occurrence of intra-population variability in its movement behaviour, which may provide some measure of resilience.
- Full Text:
- Date Issued: 2018
- Authors: Maggs, Jade Quinton
- Date: 2018
- Subjects: Fishery management -- Africa, Southern , Fisheries -- Africa, Southern , Fisheries -- Catch effort , Fisheries -- Environmental aspects , Fisheries --Monitoring , Biotelemetry , Sustainable fisheries -- Africa, Southern , Overfishing -- Africa, Southern
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/60574 , vital:27798
- Description: Movement of fishes is an integral part of their daily life, but has significant implications for fishery management. As with nearly all coastal countries, South Africa relies on coastal fisheries as a renewable resource, but many stocks have been overexploited for decades. Although it has long been recognised that an understanding of fish movement is necessary for effective management, it is with some difficulty that the subject has been studied in the past. In recent years, however, improvements in technology have provided the means for more in-depth investigations into fish movement. This research has revealed a range of complex movement behaviours. Movement in fishes occurs on a variety of temporal and spatial scales leading to the characteristic patterns of distribution and abundance observed in marine ecosystems. Fishes move nearly constantly in search of food, shelter or reproductive opportunities. Observations of behaviours such as long-term site fidelity, longdistance migration and natal homing are enabling ecologists to understand patterns of distribution and abundance within a species' range. Fish movement around the South African coast has been studied on numerous occasions but this has largely been confined to studies on single species. Movement behaviour of multiple species has been studied, but this has been limited to spatially localised marine protected area research. There has been little attempt in southern Africa to synthesize interspecific movement behaviour over wide spatial scales.Unprecedented concern over the biological effects of overexploitation, together with rapid technological advances in biotelemetry, have provided the impetus for much research, on a global scale, into the movement of marine animals. I reviewed 101 marine and estuarine fish movement studies from southern Africa, published from 1928 to 2014, with the aim of synthesising research trends and findings. Trends showed an increasing emphasis on fish movement research in publications in the sub-tropical and warm-temperate biogeographic regions along the south and east coasts of southern Africa. Although 63% of publications featured only marine studies, research into fine-scale habitat use in estuaries has been on the increase, concomitant with increasing accessibility of biotelemetry. Overall, 26 fish families were identified in the surveyed literature with regionally endemic sparids featuring in 32% of the publications. Ten movement themes were identified in the surveyed literature, including broad-scale movement patterns, which featured in 68% of studies, followed by fine- scale habitat usage (33%) and protected areas (26%). The most prominent phenomenon, emerging from this research, is that of partial migration, which describes the occurrence of resident and migratory behaviour within a coexisting animal population. Substantial progress has also been made in unravelling the complexities of fine-scale movements in marine reserves and habitat usage in estuaries. While this knowledge has enabled more effective management of South Africa's multi-user, multi-species fisheries, focus should now be directed at improving our understanding of the commonalities in movement behaviour, the associated driving forces behind this behaviour and the extent of movement across reserve boundaries. Mark-recapture data, collected over the past 30 years by the Oceanographic Research Institute’s Cooperative Fish Tagging Project (ORICFTP), were used to investigate broad- scale movement patterns of 30 prominent coastal fishery species (Chapter 4). Fishes were tagged with plastic dart tags along the coastline of southern Africa from Angola to Mozambique. This exercise yielded more than 10000 recaptures. The 30 chosen species represented 14 families, although 12 species belonged to a single family (Sparidae). Overall, 67% of recaptures were reported from the original tagging locality and 73% were recorded within 5 km of the tagging locality. The remaining observations extended from 6-3000 km. Movements were assigned to four distance bins (0-5 km, 6-50km, 51-500km and >500 km) and modelled with an ordinal logistic regression. Species, life-stage (juvenile/adult) and time- at-liberty were included as predictor variables. Model coefficients were then included in a cluster analysis, which produced two primary groupings of species (Category I and II), with two sub-groupings (Category IIa and IIb). Category I species were characterised by wide-ranging movements, greatest median recapture length and highest trophic levels. Category II species were characterised by residency, lower median recapture length and lower trophic levels. These findings have implications for fisheries management. Exploitation of resident species may lead to localised depletion, but their diffuse spatial distribution may offer some resilience. In contrast, even localised targeting of migratory species may pose a population level risk if individuals are known to aggregate. Life-cycle diversity or intra-population variability describes the existence of alternative strategies or tactics among coexisting individuals within an animal population (Chapter 5). Partial migration is a specific case of life-cycle diversity where coexisting groups exhibit either resident or migratory (wide-ranging) behaviour within a single population. Mark- recapture data collected under the auspices of the ORICFTP were used to investigate the occurrence and nature of life-cycle diversity in the movement behaviour of five non- diadromous fish species around the coastline of southern Africa. Among the five species were three teleosts (Category I and IIa) and two elasmobranchs (Category I). A fish was considered to have remained resident if recaptured within 0-5 km after 365 days at liberty. A fish was considered to have undertaken a wide-ranging movement if recaptured more than 50 km away from the release site in 365 days or less. A total of 1848 individuals from the five study species were recaptured during the study, of which 73% of the observations were classified as being resident. Binomial logistic regression confirmed that species, life-stage (juvenile/adult) and ecoregion were significant (p < 0.001) predictors of the probability of wide-ranging behaviour. A Gaussian model confirmed that species and ecoregion were also significant (p < 0.001) predictors of direction and distance of wide-ranging movement. However, the direction and distance of wide-ranging movements in juveniles did not differ significantly (p > 0.05) to that of adults. The median growth rate was mostly greater in wide- ranging individuals; however, this was only statistically significant (p < 0.05) in two cases. These findings provide unequivocal evidence of life-cycle diversity in five fish species, with vastly different life-histories. This ecological phenomenon may provide species resilience at the population level and needs to be considered in fisheries management initiatives. The movement of fishes is a fundamental aspect to consider when designing fishery management regimes. Unfortunately, traditional management strategies have often disregarded movement behaviour to the detriment of fish populations (Chapter 6). As a case study, the management of Lichia amia (Category I: wide-ranging) was evaluated in the context of its movement behaviour. Long-term catch-per-unit-effort (CPUE) datasets were examined for three South African recreational fishery sectors. The CPUE was standardised using generalized linear models (delta-Gamma/hurdle approach) to reduce the effect of factors other than abundance. Factors that were available for this purpose were year, month and locality/zone. Year was included in every model as the primary objective was to detect trends in abundance over time. Although standardised CPUE for all sectors showed an overall long-term decline, there was considerable variability in trends between the different recreational sectors and between datasets. Contrasting trends between competitive shore angling and general shore angling datasets were ascribed to hyperstability in competitive CPUE data. Hyperstability in this case was mostly influenced by rapidly improving technology, techniques and communication networks amongst competitive anglers. Month and locality were significant factors explaining the probability of catching L. amia. This suggests that the predictable aggregatory behaviour of this species could further compound the observed CPUE hyperstability. Although the CPUE responded positively for six years after implementation of the first minimum size and bag limits, and for one year after the decommercialisation of the species, these regulations and their amendments failed to arrest a long-term decline in the CPUE despite the ample evidence for hyperstability. It is clear from this case study that the predictable nature of wide-ranging behaviour in L. amia has made the population vulnerable to exploitation. This has led to the demise in the population, which could have been worse if not for the occurrence of intra-population variability in its movement behaviour, which may provide some measure of resilience.
- Full Text:
- Date Issued: 2018
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
The metabolic physiology of early stage Argyrosomus japonicus with insight into the potential effects of pCO2 induced ocean acidification
- Authors: Edworthy, Carla
- Date: 2018
- Subjects: Argyrosomus , Argyrosomus -- Growth , Argyrosomus -- Mortality , Argyrosomus -- Larvae -- Ecology , Ocean acidification , Marine ecology -- South Africa , Carbon dioxide -- Physiological effect
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/51417 , vital:26094
- Description: Ocean acidification is a phenomenon associated with global change and anthropogenic CO2 emissions that is changing the chemistry of seawater. These changes result in elevated pCO2 and reduced pH in seawater and this is impacting marine organisms in various ways. Marine fishes are considered generally tolerant to conditions of ocean acidification; however, these assumptions are based on juvenile and adult fish tolerance and the larval stages have not been frequently assessed. Furthermore, it has been suggested that temperate species, particularly those with an estuarine association, may be tolerant to variable CO2 and pH. This study used an eco-physiological approach to understand how the early life stages of Argyrosomus japonicus, an estuarine dependent marine fisheries species found in warm-temperate regions, may be impacted by ocean acidification. The metabolic response of early stage larvae (hatching to early juvenile stage) was assessed under conditions of elevated pCO2 and reduced pH in a controlled laboratory setting. Small volume static respirometry was used to determine the oxygen consumption rate of larvae raised in three pCO2 treatments including a low (pCO2 = 327.50 ± 80.07 µatm at pH 8.15), moderate (pCO2 477.40 ± 59.46 µatm at pH 8.03) and high treatment (PCO2 910.20 ± 136.45 µatm at pH 7.78). These treatment levels were relevant to the present (low) and projected conditions of ocean acidification for the years 2050 (moderate) and 2100 (high). Prior to experimentation with ocean acidification treatments, baseline metabolic rates and diurnal variation in oxygen consumption rates in early stage A. japonicus was determined. Distinct ontogenetic structuring of metabolic rates was observed in early stage A. japonicus, with no cyclical fluctuations in metabolic rate occurring during the 24 hour photoperiodic cycle. Pre-flexion larvae showed no metabolic response to ocean acidification treatments; however post-flexion stage larvae showed metabolic depression of standard metabolic rate in the moderate (32.5%) and high (9.5%) pCO2 treatments (P = 0.02). Larvae raised in the high pCO2 treatment also showed high levels of mortality with no individuals surviving past the post-flexion stage. Larvae raised in the moderate pCO2 treatment were unaffected. This study concluded that ocean acidification conditions expected for the end of the century will have significant impacts on the metabolism of early stage A. japonicus, which may result in reduced growth, retardation of skeletal development and ultimately survival as a result of increased mortality. Furthermore, the timing of reduced metabolic scope will significantly impact the recruitment ability of A. japonicus larvae into estuarine habitats. This could ultimately impact the sustainability of A. japonicus populations. Most importantly, this study highlighted the need to consider the combined effect of ontogeny and life-history strategy when assessing the vulnerability of species to ocean acidification.
- Full Text:
- Date Issued: 2018
- Authors: Edworthy, Carla
- Date: 2018
- Subjects: Argyrosomus , Argyrosomus -- Growth , Argyrosomus -- Mortality , Argyrosomus -- Larvae -- Ecology , Ocean acidification , Marine ecology -- South Africa , Carbon dioxide -- Physiological effect
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/51417 , vital:26094
- Description: Ocean acidification is a phenomenon associated with global change and anthropogenic CO2 emissions that is changing the chemistry of seawater. These changes result in elevated pCO2 and reduced pH in seawater and this is impacting marine organisms in various ways. Marine fishes are considered generally tolerant to conditions of ocean acidification; however, these assumptions are based on juvenile and adult fish tolerance and the larval stages have not been frequently assessed. Furthermore, it has been suggested that temperate species, particularly those with an estuarine association, may be tolerant to variable CO2 and pH. This study used an eco-physiological approach to understand how the early life stages of Argyrosomus japonicus, an estuarine dependent marine fisheries species found in warm-temperate regions, may be impacted by ocean acidification. The metabolic response of early stage larvae (hatching to early juvenile stage) was assessed under conditions of elevated pCO2 and reduced pH in a controlled laboratory setting. Small volume static respirometry was used to determine the oxygen consumption rate of larvae raised in three pCO2 treatments including a low (pCO2 = 327.50 ± 80.07 µatm at pH 8.15), moderate (pCO2 477.40 ± 59.46 µatm at pH 8.03) and high treatment (PCO2 910.20 ± 136.45 µatm at pH 7.78). These treatment levels were relevant to the present (low) and projected conditions of ocean acidification for the years 2050 (moderate) and 2100 (high). Prior to experimentation with ocean acidification treatments, baseline metabolic rates and diurnal variation in oxygen consumption rates in early stage A. japonicus was determined. Distinct ontogenetic structuring of metabolic rates was observed in early stage A. japonicus, with no cyclical fluctuations in metabolic rate occurring during the 24 hour photoperiodic cycle. Pre-flexion larvae showed no metabolic response to ocean acidification treatments; however post-flexion stage larvae showed metabolic depression of standard metabolic rate in the moderate (32.5%) and high (9.5%) pCO2 treatments (P = 0.02). Larvae raised in the high pCO2 treatment also showed high levels of mortality with no individuals surviving past the post-flexion stage. Larvae raised in the moderate pCO2 treatment were unaffected. This study concluded that ocean acidification conditions expected for the end of the century will have significant impacts on the metabolism of early stage A. japonicus, which may result in reduced growth, retardation of skeletal development and ultimately survival as a result of increased mortality. Furthermore, the timing of reduced metabolic scope will significantly impact the recruitment ability of A. japonicus larvae into estuarine habitats. This could ultimately impact the sustainability of A. japonicus populations. Most importantly, this study highlighted the need to consider the combined effect of ontogeny and life-history strategy when assessing the vulnerability of species to ocean acidification.
- Full Text:
- Date Issued: 2018
The spatial ecology of Albula glossodonta in the St. Joseph Atoll, Seychelles
- Authors: Moxham, Emily Jeanne
- Date: 2018
- Subjects: Bonefish -- Seychelles -- Amirante Islands , Albula -- Seychelles -- Amirante Islands , Bonefish fisheries -- Seychelles -- Amirante Islands , Small-scale fisheries -- Seychelles -- Amirante Islands -- Economic conditions , Underwater acoustic telemetry , Bonefish -- Behavior -- Seychelles -- Amirante Islands , Bonefish -- Home range -- Seychelles -- Amirante Islands , Bonefish -- Conservation -- Seychelles -- Amirante Islands , Predation (Biology) -- Seychelles -- Amirante Islands , Bonefishing
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/57863 , vital:26997
- Description: Bonefish (Albula spp.) support valuable recreational and artisanal fisheries worldwide. Declining stocks have been reported at multiple localities, potentially jeopardising numerous multimillion-dollar industries. In particular, tourism generated through bonefish fly fishing contributes considerably to the economies of many isolated tropical islands and atolls. However, despite their economic value, little is known about bonefish in the Indian Ocean. This study aimed to contribute to the understanding of bonefish ecology in the Indian Ocean by (1) reviewing the bonefish literature to identify knowledge gaps; (2) evaluating the postrelease survival of acoustically tagged bonefish and; (3) quantifying the spatial and temporal movements of bonefish at a near-pristine and predator rich atoll in the Seychelles. A review of published literature on bonefish indicated that despite considerable biological and ecological research in the Pacific and Atlantic oceans, virtually no research has been conducted in the Indian Ocean. To help address this research gap, an acoustic telemetry study was initiated at the remote St. Joseph Atoll, within an existing array of 88 automated datalogging acoustic receivers. Thirty Albula glossodonta were surgically implanted with Vemco V13 acoustic transmitters in May 2015 and tracked for a period of one year. Only 10% of the tagged bonefish were detected for more than two weeks. A comparison of the final 100 hours of movement data from fish that were detected for less than two weeks to fish detected for longer periods revealed distinct differences. These included differences in area use patterns and significant differences in the average daily distance moved, speed of movement and residency index. This suggested that mortality in the form of post-release predation was high (90%) with tagged fish detected for less than two weeks being preyed upon by sharks. The three surviving bonefish were tracked for 210 to 367 days. These individuals remained in the atoll and showed high use of the marginal habitats between the shallow sand flats and the deeper lagoon. Water temperature, diel cycle and tide were significant predictors of bonefish presence in the lagoon. The high post-release predation of bonefish has implications for the management of this and other Albula species. Despite these fisheries being catch-and-release, bonefish fishing may be unsustainable due to the high post-release mortality, particularly in areas that are rich in predators. Therefore, protected areas or limitations on fishing effort need to be considered.
- Full Text:
- Date Issued: 2018
- Authors: Moxham, Emily Jeanne
- Date: 2018
- Subjects: Bonefish -- Seychelles -- Amirante Islands , Albula -- Seychelles -- Amirante Islands , Bonefish fisheries -- Seychelles -- Amirante Islands , Small-scale fisheries -- Seychelles -- Amirante Islands -- Economic conditions , Underwater acoustic telemetry , Bonefish -- Behavior -- Seychelles -- Amirante Islands , Bonefish -- Home range -- Seychelles -- Amirante Islands , Bonefish -- Conservation -- Seychelles -- Amirante Islands , Predation (Biology) -- Seychelles -- Amirante Islands , Bonefishing
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/57863 , vital:26997
- Description: Bonefish (Albula spp.) support valuable recreational and artisanal fisheries worldwide. Declining stocks have been reported at multiple localities, potentially jeopardising numerous multimillion-dollar industries. In particular, tourism generated through bonefish fly fishing contributes considerably to the economies of many isolated tropical islands and atolls. However, despite their economic value, little is known about bonefish in the Indian Ocean. This study aimed to contribute to the understanding of bonefish ecology in the Indian Ocean by (1) reviewing the bonefish literature to identify knowledge gaps; (2) evaluating the postrelease survival of acoustically tagged bonefish and; (3) quantifying the spatial and temporal movements of bonefish at a near-pristine and predator rich atoll in the Seychelles. A review of published literature on bonefish indicated that despite considerable biological and ecological research in the Pacific and Atlantic oceans, virtually no research has been conducted in the Indian Ocean. To help address this research gap, an acoustic telemetry study was initiated at the remote St. Joseph Atoll, within an existing array of 88 automated datalogging acoustic receivers. Thirty Albula glossodonta were surgically implanted with Vemco V13 acoustic transmitters in May 2015 and tracked for a period of one year. Only 10% of the tagged bonefish were detected for more than two weeks. A comparison of the final 100 hours of movement data from fish that were detected for less than two weeks to fish detected for longer periods revealed distinct differences. These included differences in area use patterns and significant differences in the average daily distance moved, speed of movement and residency index. This suggested that mortality in the form of post-release predation was high (90%) with tagged fish detected for less than two weeks being preyed upon by sharks. The three surviving bonefish were tracked for 210 to 367 days. These individuals remained in the atoll and showed high use of the marginal habitats between the shallow sand flats and the deeper lagoon. Water temperature, diel cycle and tide were significant predictors of bonefish presence in the lagoon. The high post-release predation of bonefish has implications for the management of this and other Albula species. Despite these fisheries being catch-and-release, bonefish fishing may be unsustainable due to the high post-release mortality, particularly in areas that are rich in predators. Therefore, protected areas or limitations on fishing effort need to be considered.
- Full Text:
- Date Issued: 2018
Towards understanding the effect of size variation on the aggressive and feeding behaviours of juvenile dusky kob Argyrosomus japonicus (Pisces: Sciaenidae)
- Authors: Babane, Siviwe Elvis
- Date: 2018
- Subjects: Argyrosomus -- Feeding and feeds , Aquaculture , Fishes -- Cannibalism , Fishes -- Feeding and feeds
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/59592 , vital:27629
- Description: Many studies have been conducted on the effect of size-grading in other fish species. However, there is a paucity of scientific information on the effects of size variation on cannibalism of juvenile dusky kob. Thus, a study focusing on the effect of size variation on juvenile dusky kob aggressive and feeding (browsing) behaviours was conducted. Three separate groups of hatchery-reared juvenile dusky kob of were obtained from Oceanwise (Pty) Ltd for use in a series of three experimental trials. In all trials, juvenile fish of the same age were size-graded and the COV-value was used to determine the size variation. The focal fish (largest fish) was exposed to groups of fish with different size variation for 30-min. behavioural observations before and after feeding in randomised trials. The first experimental trial (Chapter 2) quantified the effect of increasing size variation and observation time on the aggressive and browsing behaviours of juvenile dusky kob. On average, juvenile dusky kob weighed 3.60 ± 0.68 g fish-1 and measured 5.8 ± 0.41 mm. Each focal fish was observed (a) before feeding in the morning, (b) 2 h after feeding, (c) 6 h after feeding and (d) 12 h after feeding. Fish increased browsing behaviours (averaging 6.60 ± 0.56) and decreased intimidating aggressive behaviours (18.60 ± 1.39) 12 h after feeding. Other aggressive behaviours occurred but did not differ between observation times. Aggressive and browsing behaviours positively correlated with size variation variables, predominantly, 12 h after feeding. An average frequency of 19 chases were observed positively correlated with size variation, followed by average frequencies of 17 body bites and browses, and 11 tail bites per 30 min. Some behaviours including average frequencies of 0.2 chases, 4 tail bites, 2.4 intimidating and 0.3 browsing behaviours negatively correlated with the size variation, generally closer to the last meal. These preliminary observations thus showed that fish have become hungry approximately 6-12 h after feeding and substituted certain behaviours for others as time after feeding passed and as size variation increased. The second experimental trial (Chapter 3) consisted of the observations further testing the relationship between aggressive behaviours and size variation of juveniles of dusky kob averaging 0.43 ± 0.27 g fish-1. The focal fish was exposed to groups of fish of four size variation (COV) treatments for observations before and 12 h after feeding. Aggressive behaviours positively correlated with size variation both before and 12 h after feeding. An average frequency of 437 body bites positively correlated more often with COV, followed by average frequencies of 365 intimidating behaviours and 199 tail bites per 30 min., respectively, before and 12 h after feeding. The least often exhibited aggressive behaviours averaged 26 chases while positively correlating with size variation on the times specified. An average frequency of 311 intimidating behaviours before and after feeding including average of 28 tail bites after feeding negatively correlated with size variation. This may relate to shift of behaviours depending on the needs and capacity of the fish. Apparently, aggressive fish can change its behaviour as a function of COV-values rather than the mean size of the other fish. The third trial (Chapter 4) investigated the effect of the aggressor’s (focal fish) size in relation its aggressive and browsing behaviours to other fish (non-focal fish). Juvenile fish used for this trial, on average, weighed 30 ± 7.63 g fish-1. Aggressive and browsing behaviours were observed in four treatments of a) high COV and mean weight below, b) low COV and mean weight less, c) high COV and mean weight equivalent to and d) low COV and mean weight higher than that of the focal fish. Increased frequencies of aggressive and browsing behaviours per 30 min. occurred in treatment A, sharing similar frequencies in treatment C, compared to the other treatments (B and D) which shared certain frequencies. The intimidating behaviours predominated, followed by browsing, body bites, chases and tail bites, respectively. The results of the overall study suggest that the time passed after feeding and increasing size variation and differences facilitated aggressive and browsing behaviours in juvenile dusky kob. Dusky kob showed increasing aggressive behaviours as early as in the first two weeks after hatching, averaging 0.43 ± 0.27 g fish-1 with the frequency correlating with size differences. Consistent size-grading technique in the same-age fish should be used to manage size variation associated with aggressive behaviours. The period of about 4-6 h after feeding may explain the noticeable increased aggressive and browsing behaviours. Thus, fish should be fed immediately before or after evacuation of their guts to maintain less-aggressive behaviours of juvenile dusky kob. Fish generally increased aggressive and browsing acts before and long time after feeding than closer to after feeding. The study has provided the fundamental scientific groundwork for fish farmers and future researchers can further explore size variation, time after feeding and gut evacuation rate as critical components of aggressive behaviours. The scientific knowledge of aggressive and cannibalistic behaviours has essential application in farming management to achieve improved survival and growth rates in juvenile fish.
- Full Text:
- Date Issued: 2018
- Authors: Babane, Siviwe Elvis
- Date: 2018
- Subjects: Argyrosomus -- Feeding and feeds , Aquaculture , Fishes -- Cannibalism , Fishes -- Feeding and feeds
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/59592 , vital:27629
- Description: Many studies have been conducted on the effect of size-grading in other fish species. However, there is a paucity of scientific information on the effects of size variation on cannibalism of juvenile dusky kob. Thus, a study focusing on the effect of size variation on juvenile dusky kob aggressive and feeding (browsing) behaviours was conducted. Three separate groups of hatchery-reared juvenile dusky kob of were obtained from Oceanwise (Pty) Ltd for use in a series of three experimental trials. In all trials, juvenile fish of the same age were size-graded and the COV-value was used to determine the size variation. The focal fish (largest fish) was exposed to groups of fish with different size variation for 30-min. behavioural observations before and after feeding in randomised trials. The first experimental trial (Chapter 2) quantified the effect of increasing size variation and observation time on the aggressive and browsing behaviours of juvenile dusky kob. On average, juvenile dusky kob weighed 3.60 ± 0.68 g fish-1 and measured 5.8 ± 0.41 mm. Each focal fish was observed (a) before feeding in the morning, (b) 2 h after feeding, (c) 6 h after feeding and (d) 12 h after feeding. Fish increased browsing behaviours (averaging 6.60 ± 0.56) and decreased intimidating aggressive behaviours (18.60 ± 1.39) 12 h after feeding. Other aggressive behaviours occurred but did not differ between observation times. Aggressive and browsing behaviours positively correlated with size variation variables, predominantly, 12 h after feeding. An average frequency of 19 chases were observed positively correlated with size variation, followed by average frequencies of 17 body bites and browses, and 11 tail bites per 30 min. Some behaviours including average frequencies of 0.2 chases, 4 tail bites, 2.4 intimidating and 0.3 browsing behaviours negatively correlated with the size variation, generally closer to the last meal. These preliminary observations thus showed that fish have become hungry approximately 6-12 h after feeding and substituted certain behaviours for others as time after feeding passed and as size variation increased. The second experimental trial (Chapter 3) consisted of the observations further testing the relationship between aggressive behaviours and size variation of juveniles of dusky kob averaging 0.43 ± 0.27 g fish-1. The focal fish was exposed to groups of fish of four size variation (COV) treatments for observations before and 12 h after feeding. Aggressive behaviours positively correlated with size variation both before and 12 h after feeding. An average frequency of 437 body bites positively correlated more often with COV, followed by average frequencies of 365 intimidating behaviours and 199 tail bites per 30 min., respectively, before and 12 h after feeding. The least often exhibited aggressive behaviours averaged 26 chases while positively correlating with size variation on the times specified. An average frequency of 311 intimidating behaviours before and after feeding including average of 28 tail bites after feeding negatively correlated with size variation. This may relate to shift of behaviours depending on the needs and capacity of the fish. Apparently, aggressive fish can change its behaviour as a function of COV-values rather than the mean size of the other fish. The third trial (Chapter 4) investigated the effect of the aggressor’s (focal fish) size in relation its aggressive and browsing behaviours to other fish (non-focal fish). Juvenile fish used for this trial, on average, weighed 30 ± 7.63 g fish-1. Aggressive and browsing behaviours were observed in four treatments of a) high COV and mean weight below, b) low COV and mean weight less, c) high COV and mean weight equivalent to and d) low COV and mean weight higher than that of the focal fish. Increased frequencies of aggressive and browsing behaviours per 30 min. occurred in treatment A, sharing similar frequencies in treatment C, compared to the other treatments (B and D) which shared certain frequencies. The intimidating behaviours predominated, followed by browsing, body bites, chases and tail bites, respectively. The results of the overall study suggest that the time passed after feeding and increasing size variation and differences facilitated aggressive and browsing behaviours in juvenile dusky kob. Dusky kob showed increasing aggressive behaviours as early as in the first two weeks after hatching, averaging 0.43 ± 0.27 g fish-1 with the frequency correlating with size differences. Consistent size-grading technique in the same-age fish should be used to manage size variation associated with aggressive behaviours. The period of about 4-6 h after feeding may explain the noticeable increased aggressive and browsing behaviours. Thus, fish should be fed immediately before or after evacuation of their guts to maintain less-aggressive behaviours of juvenile dusky kob. Fish generally increased aggressive and browsing acts before and long time after feeding than closer to after feeding. The study has provided the fundamental scientific groundwork for fish farmers and future researchers can further explore size variation, time after feeding and gut evacuation rate as critical components of aggressive behaviours. The scientific knowledge of aggressive and cannibalistic behaviours has essential application in farming management to achieve improved survival and growth rates in juvenile fish.
- Full Text:
- Date Issued: 2018
Two-tissue stable isotope analysis to elucidate isotopic incorporation and trophic niche patterns for chubbyhead barb Enteromius anoplus
- Authors: Kambikambi, Manda Juliet
- Date: 2018
- Subjects: Food chains (Ecology) , Barbus -- South Africa -- Great Fish River Estuary , Stable isotopes , Freshwater fishes -- Feeding and feeds , Freshwater fishes -- Food , Fins (Anatomy) , Akaike Information Criterion , Freshwater fishes -- Conservation , Chubbyhead barb Enteromius anoplus
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/61906 , vital:28082
- Description: Knowledge of trophic ecology underpins conservation and management of threatened species. Stable isotope analysis has been widely used as a more objective approach for elucidating the trophic positions of freshwater fishes. Until recently, stable isotope analysis for trophic ecology studies in freshwater fishes largely utilised white muscle tissue. This sampling approach, however, involves either euthanasia or muscle biopsy procedures that may be inappropriate for small-sized and endangered fishes. These concerns raised the need to explore and validate the utility of non-lethal alternatives such as fin clips, mucus and scales. The present study investigated the use of caudal fin tissue as a potential non-lethal alternative to muscle tissue for trophic studies on the chubbyhead barb Enteromius anoplus. The chubbyhead barb was selected as a model taxon for the present study because it is closely related or comparable in body size to a number of highly threatened small-bodied minnows in southern Africa. The chubbyhead barb was also considered an ideal species for this study because it is widespread, abundant and classified as Least Concern on the IUCN list of threatened species. The study used a two-pronged approach based on laboratory and field experiments. A laboratory experiment was conducted to quantify isotopic turnover rates and diet-tissue discrimination factors (DTDFs/A) for both muscle and fin tissues. This involved feeding chubbyhead barb two diets with distinct carbon (δ13C) and nitrogen (δ15N) values, and monitoring the temporal isotopic incorporation patterns into the two tissues. These patterns were assessed by applying least squares non-linear one- and two-compartment isotopic kinetics models. Model comparisons, based on Akaike information criterion (AIC), revealed that one- compartment models described isotopic incorporation patterns better than two-compartment models for both muscle and fin tissues. For δ13C, relatively short and comparable turnover rates were observed for muscle and fin tissues, which suggests that fin tissue could potentially provide similar inference as muscle tissue when assessing short term dietary patterns for chubbyhead barb. In contrast to δ13C, turnover rates for δ15N between muscle and fin tissue were different for both diets. Specifically, stable isotope incorporation turnover rate was faster in muscle tissue for animals that were fed on isotopically enriched diets compared to fin tissue. Conversely, stable isotope incorporation into fin tissue was faster in animals fed on isotopically depleted diets compared to muscle tissue. This suggests that knowledge of animal diet is critical when inferring fin tissue δ15N turnover rates, particularly when extrapolating both short and long term dietary patterns. Diet-tissue discrimination factors were influenced by diet type, with the fish fed on isotopically enriched diet having lower DTDFs than animals fed on isotopically depleted diets. This variation may be explained by the protein quality hypothesis, which suggests that the DTDFs of consumers will decrease as protein quality increases. When A13C and A15N values were averaged across diets in muscle and fin tissue, the values were 0.74‰ and 0.64‰, respectively, for A13C, and 5.53‰ and 5.83 ‰, respectively, for A15N. This appeared to be consistent with studies on other taxa for A13C (0-1 ‰), but for A15N (3-5 ‰) the results of this study were higher than those reported for other taxa. These results suggest that investigating appropriate DTDFs for both muscle and fin tissues is important in trophic ecology studies of these minnows. A field-based study was conducted to investigate temporal dynamics in food web patterns for chubbyhead barb in the wild within the headwaters of the Koonap River, a tributary of the Great Fish River, in the Eastern Cape, South Africa. This was achieved by collecting and comparing stable isotope data for chubbyhead barb and its potential food sources on a seasonal scale. There was a discernible difference in both the composition of carbon and nitrogen isotope values for basal food sources and macroinvertebrate communities, which suggests that this headwater stream was subject to temporal changes in food web dynamics. For chubbyhead barb, comparison of its isotopic niche sizes on a temporal scale based on both muscle and fin tissue showed differences across seasons. Furthermore, isotopic niche sizes inferred from fin tissue were larger than those inferred from muscle tissue during winter and spring, whereas during summer and autumn the isotopic niche sizes inferred from muscle and fin tissue were generally comparable. This suggests the likely influence of different metabolic and physiological processes that these two tissues undergo on a temporal scale. Therefore, difference in tissue type, and their associated metabolic pathways should be considered when using fin tissue as a substitute for muscle tissue on broad temporal scales. The results from this study indicated that caudal fin tissue has the potential to be a substitute for muscle in trophic studies of chubbyhead barb Enteromius anoplus, as well as other related small bodied endangered minnow species from South Africa.
- Full Text:
- Date Issued: 2018
- Authors: Kambikambi, Manda Juliet
- Date: 2018
- Subjects: Food chains (Ecology) , Barbus -- South Africa -- Great Fish River Estuary , Stable isotopes , Freshwater fishes -- Feeding and feeds , Freshwater fishes -- Food , Fins (Anatomy) , Akaike Information Criterion , Freshwater fishes -- Conservation , Chubbyhead barb Enteromius anoplus
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/61906 , vital:28082
- Description: Knowledge of trophic ecology underpins conservation and management of threatened species. Stable isotope analysis has been widely used as a more objective approach for elucidating the trophic positions of freshwater fishes. Until recently, stable isotope analysis for trophic ecology studies in freshwater fishes largely utilised white muscle tissue. This sampling approach, however, involves either euthanasia or muscle biopsy procedures that may be inappropriate for small-sized and endangered fishes. These concerns raised the need to explore and validate the utility of non-lethal alternatives such as fin clips, mucus and scales. The present study investigated the use of caudal fin tissue as a potential non-lethal alternative to muscle tissue for trophic studies on the chubbyhead barb Enteromius anoplus. The chubbyhead barb was selected as a model taxon for the present study because it is closely related or comparable in body size to a number of highly threatened small-bodied minnows in southern Africa. The chubbyhead barb was also considered an ideal species for this study because it is widespread, abundant and classified as Least Concern on the IUCN list of threatened species. The study used a two-pronged approach based on laboratory and field experiments. A laboratory experiment was conducted to quantify isotopic turnover rates and diet-tissue discrimination factors (DTDFs/A) for both muscle and fin tissues. This involved feeding chubbyhead barb two diets with distinct carbon (δ13C) and nitrogen (δ15N) values, and monitoring the temporal isotopic incorporation patterns into the two tissues. These patterns were assessed by applying least squares non-linear one- and two-compartment isotopic kinetics models. Model comparisons, based on Akaike information criterion (AIC), revealed that one- compartment models described isotopic incorporation patterns better than two-compartment models for both muscle and fin tissues. For δ13C, relatively short and comparable turnover rates were observed for muscle and fin tissues, which suggests that fin tissue could potentially provide similar inference as muscle tissue when assessing short term dietary patterns for chubbyhead barb. In contrast to δ13C, turnover rates for δ15N between muscle and fin tissue were different for both diets. Specifically, stable isotope incorporation turnover rate was faster in muscle tissue for animals that were fed on isotopically enriched diets compared to fin tissue. Conversely, stable isotope incorporation into fin tissue was faster in animals fed on isotopically depleted diets compared to muscle tissue. This suggests that knowledge of animal diet is critical when inferring fin tissue δ15N turnover rates, particularly when extrapolating both short and long term dietary patterns. Diet-tissue discrimination factors were influenced by diet type, with the fish fed on isotopically enriched diet having lower DTDFs than animals fed on isotopically depleted diets. This variation may be explained by the protein quality hypothesis, which suggests that the DTDFs of consumers will decrease as protein quality increases. When A13C and A15N values were averaged across diets in muscle and fin tissue, the values were 0.74‰ and 0.64‰, respectively, for A13C, and 5.53‰ and 5.83 ‰, respectively, for A15N. This appeared to be consistent with studies on other taxa for A13C (0-1 ‰), but for A15N (3-5 ‰) the results of this study were higher than those reported for other taxa. These results suggest that investigating appropriate DTDFs for both muscle and fin tissues is important in trophic ecology studies of these minnows. A field-based study was conducted to investigate temporal dynamics in food web patterns for chubbyhead barb in the wild within the headwaters of the Koonap River, a tributary of the Great Fish River, in the Eastern Cape, South Africa. This was achieved by collecting and comparing stable isotope data for chubbyhead barb and its potential food sources on a seasonal scale. There was a discernible difference in both the composition of carbon and nitrogen isotope values for basal food sources and macroinvertebrate communities, which suggests that this headwater stream was subject to temporal changes in food web dynamics. For chubbyhead barb, comparison of its isotopic niche sizes on a temporal scale based on both muscle and fin tissue showed differences across seasons. Furthermore, isotopic niche sizes inferred from fin tissue were larger than those inferred from muscle tissue during winter and spring, whereas during summer and autumn the isotopic niche sizes inferred from muscle and fin tissue were generally comparable. This suggests the likely influence of different metabolic and physiological processes that these two tissues undergo on a temporal scale. Therefore, difference in tissue type, and their associated metabolic pathways should be considered when using fin tissue as a substitute for muscle tissue on broad temporal scales. The results from this study indicated that caudal fin tissue has the potential to be a substitute for muscle in trophic studies of chubbyhead barb Enteromius anoplus, as well as other related small bodied endangered minnow species from South Africa.
- 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
Abalone stock enhancement at Cape Recife, Eastern Cape Province of South Africa
- Authors: Witte, Warren
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/45695 , vital:25532
- Description: The potential for restocking depleted natural reefs with hatchery abalone, Haliotis midae, to support a commercial ranching venture in the Eastern Cape Province of South Africa was investigated. A baseline stock assessment and analysis of historical fishery data provided compelling evidence of significant declines in the abalone stock, attributed to uncontrolled illegal fishing over the last 20 years at the study site. A ranching pilot study was undertaken where small-scale replicated seeding experiments were set up which quantified the effect of seed size, density and habitat on survival and growth of hatchery-reared abalone. Thirty-six experimental plots were seeded with 8400 abalone spread evenly over two broad habitats. Mean retrievals of seeded abalone were 17% ranging from 4 - 42% after a minimum of eight months at large. Release density and large-scale habitat had no significant effect on seed survival, but smaller seed size (40.0 ±3.7mm shell length) achieved higher (F1, 22 = 4.64, p = 0.042) retrievals than larger seed size (53 ±3.7mm). Growth rates were an average of 30% higher in the shallow sites compared deeper sites (t1, 1091 = -2.79, p = 0.005). There was seasonal component in growth with a 0.55 ± 0.04 mm per month higher rate in summer than during winter (t1, 1091 = -12.45, p < 0.001). Abalone seed releases were also conducted on a larger scale, which focused on the economic potential for commercial-scale ranching. Over 160 sites were seeded with 1.4 million hatchery reared abalone or 30 metric tonnes. Seventeen sites underwent long-term monitoring of survival with repeated sampling events on sites over a period of up to 666 days. Nine of these sites were seeded with 140800 small abalone (29 – 40 mm), three sites with 25100 medium abalone (30 – 46 mm) and five sites with 14700 large abalone (60 – 84 mm). There was a significant difference in survival between the seed sizes (F4,6329 = 304.3, P < 0.001). The Generalized Linear Mixed Model (GLMM) calculation estimated the instantaneous apparent mortality rate for small, medium and large abalone at 1.19 yr-1 , -0.9 yr-1 and -0.67 yr-1 , which equated to a survival rate of 21%, 28% and 36% per year respectively. The weighted mortality rate calculated according to the seed size differential mortality and the number of seed released for those sizes was 1 yr-1 or 25% survival. In conjunction with a conservative somatic growth rate of 1.2mm.m-1 and plausible emigration rates, a range of biomass harvesting estimates were obtained. Movement and mortality were investigated using video analysis which showed that hatchery seed had the ability to move considerably once released onto natural reefs and confirmed that mortality immediately following releases was due to the heavy predation pressure as confirmed by shell collections. This project has demonstrated that potential exists for ranching in South Africa and highlights critical factors that need to be addressed if ranching is to be an economically viable operation.
- Full Text:
- Date Issued: 2017
- Authors: Witte, Warren
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/45695 , vital:25532
- Description: The potential for restocking depleted natural reefs with hatchery abalone, Haliotis midae, to support a commercial ranching venture in the Eastern Cape Province of South Africa was investigated. A baseline stock assessment and analysis of historical fishery data provided compelling evidence of significant declines in the abalone stock, attributed to uncontrolled illegal fishing over the last 20 years at the study site. A ranching pilot study was undertaken where small-scale replicated seeding experiments were set up which quantified the effect of seed size, density and habitat on survival and growth of hatchery-reared abalone. Thirty-six experimental plots were seeded with 8400 abalone spread evenly over two broad habitats. Mean retrievals of seeded abalone were 17% ranging from 4 - 42% after a minimum of eight months at large. Release density and large-scale habitat had no significant effect on seed survival, but smaller seed size (40.0 ±3.7mm shell length) achieved higher (F1, 22 = 4.64, p = 0.042) retrievals than larger seed size (53 ±3.7mm). Growth rates were an average of 30% higher in the shallow sites compared deeper sites (t1, 1091 = -2.79, p = 0.005). There was seasonal component in growth with a 0.55 ± 0.04 mm per month higher rate in summer than during winter (t1, 1091 = -12.45, p < 0.001). Abalone seed releases were also conducted on a larger scale, which focused on the economic potential for commercial-scale ranching. Over 160 sites were seeded with 1.4 million hatchery reared abalone or 30 metric tonnes. Seventeen sites underwent long-term monitoring of survival with repeated sampling events on sites over a period of up to 666 days. Nine of these sites were seeded with 140800 small abalone (29 – 40 mm), three sites with 25100 medium abalone (30 – 46 mm) and five sites with 14700 large abalone (60 – 84 mm). There was a significant difference in survival between the seed sizes (F4,6329 = 304.3, P < 0.001). The Generalized Linear Mixed Model (GLMM) calculation estimated the instantaneous apparent mortality rate for small, medium and large abalone at 1.19 yr-1 , -0.9 yr-1 and -0.67 yr-1 , which equated to a survival rate of 21%, 28% and 36% per year respectively. The weighted mortality rate calculated according to the seed size differential mortality and the number of seed released for those sizes was 1 yr-1 or 25% survival. In conjunction with a conservative somatic growth rate of 1.2mm.m-1 and plausible emigration rates, a range of biomass harvesting estimates were obtained. Movement and mortality were investigated using video analysis which showed that hatchery seed had the ability to move considerably once released onto natural reefs and confirmed that mortality immediately following releases was due to the heavy predation pressure as confirmed by shell collections. This project has demonstrated that potential exists for ranching in South Africa and highlights critical factors that need to be addressed if ranching is to be an economically viable operation.
- Full Text:
- Date Issued: 2017
Apparent digestibility coefficients of feed ingredients and essential amino acid requirements of dusky kob (Argyrosomus japonicus)
- Authors: Adesola, Abidemi Adejoke
- Date: 2017
- Subjects: Amino acids in animal nutrition , Fishes -- Feeding and feeds , Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Nutrition , Argyrosomus -- Nutrition , Argyrosomus japonicus -- Feeding and feeds , Argyrosomus -- Feeding and feeds
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/32140 , vital:24014
- Description: Important to the evaluation of potential feed ingredients for inclusion in fish diets should be their digestibility and amino acid requirement so that feeds can be formulated on a digestible basis rather than a gross nutrient basis. This thesis established techniques for faecal collection, the validity of digestibility markers, it determined apparent digestibility coefficients for various novel feed ingredients, and it established the optimal lysine requirement for Argyrosomus japonicus, which was used to estimate each of the essential amino acid requirements by using the ideal protein concept. There were no significant differences in dry matter apparent digestibility coefficients when faeces were collected by stripping (77.0 %), dissection (80.1 %) or settlement (83.5 %). Faecal collection by the settlement method produced the most reliable digestibility data. Apparent digestibility coefficients for dry matter, crude protein and energy calculated using acid-insoluble ash were higher (84.0 %, 93.2 % and 93.0 %, respectively) than those using chromic oxide (55.7 %, 79.1 % and 78.2 %) and titanium dioxide (58.6 %, 79.7 % and 80.5 %). The magnitude of variation in digestibility coefficients obtained using acid-insoluble ash was always lower than that obtained with the other markers. Therefore, acid-insoluble ash was preferred as a dietary marker. Using the above protocol, protein and amino acid digestibility of some animal and plant protein ingredients were evaluated in a series of experiments. The first trial compared the apparent digestibility coefficients of some animal products included as single protein source in the test diets. Apparent protein digestibility values were 84.5 %, 83.8 %, 85.8 % and 83.1 % for fishmeal-prime, fishmeal-standard, poultry meal and pork meal, respectively. Apparent digestibility coefficients for poultry meal were comparable to those of fishmeal, which indicate its potential as a substitute for fishmeal in the diets of A. japonicus. The second trial determined the apparent coefficients of plant and animal protein sources included at 30 % into a practical reference diet (70 %). Apparent protein digestibility ranged from 92.4 % in sunflower meal to 85.5 % in corn gluten meal. Soybean meal is a promising feed ingredient in A. japonicus due to the high apparent digestibility of its protein (92.0 %) and essential amino acid digestibility (mean average 91.4 %). A fundamental assumption in fish feed formulation is that the digestibility of nutrients is additive, i.e., digestibility of a nutrient in one ingredient does not interact with the digestibility of the same nutrient in another ingredient. In the third trial, additivity of feed ingredients was tested using pork meal and poultry meal. The results indicate that the apparent digestibility coefficient of animal protein ingredients could be calculated from compound diets to accurately determine protein and amino acid digestibility in A. japonicus, and possibly other carnivorous fish species. Dietary essential amino acid requirements were determined for juvenile A. japonicus in two trials. A dose-response study was conducted using crystalline lysine to determine the optimal requirement of dietary lysine for A. japonicus. Optimal dietary lysine was estimated at 31.7 g kg-¹ dry diet, corresponding to 73.5 g kg-¹ of dietary protein, based on specific growth rate and broken-line segmented regression analyses. Dietary requirements for other essential amino acids ranged from 22 g kg-¹ (histidine) to 71 g kg-¹ (leucine) crude protein. The results of the present study provided a research tool that could be used to assess and verify the conclusions of earlier dietary work on A. japonicus and in further studies to develop least cost diet formulations for this species. The study also adds to the knowledge of the nutritional requirements of A. japonicus by providing information on the digestibility of plants and animal protein ingredients. It also contributes to future dietary research for this species because this study determines, for the first time, the most suitable methods for investigating the digestibility of raw materials for A. japonicus.
- Full Text:
- Date Issued: 2017
- Authors: Adesola, Abidemi Adejoke
- Date: 2017
- Subjects: Amino acids in animal nutrition , Fishes -- Feeding and feeds , Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Nutrition , Argyrosomus -- Nutrition , Argyrosomus japonicus -- Feeding and feeds , Argyrosomus -- Feeding and feeds
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/32140 , vital:24014
- Description: Important to the evaluation of potential feed ingredients for inclusion in fish diets should be their digestibility and amino acid requirement so that feeds can be formulated on a digestible basis rather than a gross nutrient basis. This thesis established techniques for faecal collection, the validity of digestibility markers, it determined apparent digestibility coefficients for various novel feed ingredients, and it established the optimal lysine requirement for Argyrosomus japonicus, which was used to estimate each of the essential amino acid requirements by using the ideal protein concept. There were no significant differences in dry matter apparent digestibility coefficients when faeces were collected by stripping (77.0 %), dissection (80.1 %) or settlement (83.5 %). Faecal collection by the settlement method produced the most reliable digestibility data. Apparent digestibility coefficients for dry matter, crude protein and energy calculated using acid-insoluble ash were higher (84.0 %, 93.2 % and 93.0 %, respectively) than those using chromic oxide (55.7 %, 79.1 % and 78.2 %) and titanium dioxide (58.6 %, 79.7 % and 80.5 %). The magnitude of variation in digestibility coefficients obtained using acid-insoluble ash was always lower than that obtained with the other markers. Therefore, acid-insoluble ash was preferred as a dietary marker. Using the above protocol, protein and amino acid digestibility of some animal and plant protein ingredients were evaluated in a series of experiments. The first trial compared the apparent digestibility coefficients of some animal products included as single protein source in the test diets. Apparent protein digestibility values were 84.5 %, 83.8 %, 85.8 % and 83.1 % for fishmeal-prime, fishmeal-standard, poultry meal and pork meal, respectively. Apparent digestibility coefficients for poultry meal were comparable to those of fishmeal, which indicate its potential as a substitute for fishmeal in the diets of A. japonicus. The second trial determined the apparent coefficients of plant and animal protein sources included at 30 % into a practical reference diet (70 %). Apparent protein digestibility ranged from 92.4 % in sunflower meal to 85.5 % in corn gluten meal. Soybean meal is a promising feed ingredient in A. japonicus due to the high apparent digestibility of its protein (92.0 %) and essential amino acid digestibility (mean average 91.4 %). A fundamental assumption in fish feed formulation is that the digestibility of nutrients is additive, i.e., digestibility of a nutrient in one ingredient does not interact with the digestibility of the same nutrient in another ingredient. In the third trial, additivity of feed ingredients was tested using pork meal and poultry meal. The results indicate that the apparent digestibility coefficient of animal protein ingredients could be calculated from compound diets to accurately determine protein and amino acid digestibility in A. japonicus, and possibly other carnivorous fish species. Dietary essential amino acid requirements were determined for juvenile A. japonicus in two trials. A dose-response study was conducted using crystalline lysine to determine the optimal requirement of dietary lysine for A. japonicus. Optimal dietary lysine was estimated at 31.7 g kg-¹ dry diet, corresponding to 73.5 g kg-¹ of dietary protein, based on specific growth rate and broken-line segmented regression analyses. Dietary requirements for other essential amino acids ranged from 22 g kg-¹ (histidine) to 71 g kg-¹ (leucine) crude protein. The results of the present study provided a research tool that could be used to assess and verify the conclusions of earlier dietary work on A. japonicus and in further studies to develop least cost diet formulations for this species. The study also adds to the knowledge of the nutritional requirements of A. japonicus by providing information on the digestibility of plants and animal protein ingredients. It also contributes to future dietary research for this species because this study determines, for the first time, the most suitable methods for investigating the digestibility of raw materials for A. japonicus.
- Full Text:
- Date Issued: 2017
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
Diurnal and nocturnal activity patterns and habitat use of Algoa Bay’s rocky reef fish community
- Authors: Juby, Roxanne
- Date: 2017
- Subjects: Reef fishes -- Effect of light on , Reef fishes -- South Africa , Underwater videography in wildlife monitoring -- South Africa -- Tsitsikamma
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/44827 , vital:25445
- Description: Distinct day-night changes in ambient light are recognised as an important driver of animal activity patterns, with predictable changes to the structure and composition of animal communities between day and night. While day-night variation in the structure of animal communities has been well researched for terrestrial organisms and shallow marine fish communities around the world, there has been limited research of this type conducted on South Africa’s rocky reef fish communities. Consequently, we have a poor understanding of how nocturnal reef fish communities are structured and the day-night activity patterns of species inhabiting both shallow (10-30m) and deep-aphotic (55-100m) reefs. This research was conducted at two warm-temperate South African rocky reefs situated in Algoa Bay. The importance of natural ambient light in shaping the distribution of reef fish communities at shallow and deep-aphotic reef sites was demonstrated using baited remote underwater stereo-video systems (stereo-BRUVs). Distinct day and night fish communities were sampled at shallow and deep-aphotic reef sites. These differences were driven by significant changes in species richness (p < 0.001), species abundance (p < 0.001) and community composition (p < 0.001). These shifts appeared to be driven by day-night activity patterns that were the result of increased detectability of certain species at either day or night. The majority of species belonging to the family Sparidae showed evidence of strict diurnal activity, with their activity being further restricted to shallow reefs. These species showed evidence that they may enter micro-habitats within the reef at night. Similar activity patterns were shown for other top predatory teleost species and low level consumers, with substantial reductions in abundances, or no recordings at night throughout this study. Shallow reefs at day harboured the most diverse fish community. It is therefore hypothesised that this habitat was associated with conditions that offered improved access to resources for many visual species. In addition, the diverse community inhabiting shallow reefs at day is associated with a high risk of negative interspecies interactions, such as competition and predation. It is hypothesised that the biotic conditions associated with shallow reefs at day drove three movement patterns identified in this study; Pagellus bellottii natalensis showed evidence of movement onto shallow reefs at night from adjacent sandy flats, while Pterogymnus laniarius and Squalus sp. 1 showed evidence of movement onto shallow reefs at night from the deep- aphotic reefs that remain dark throughout the diel cycle. It is further hypothesised that other species which showed evidence for nocturnal activity, i.e. Galeichthys ater, Eptatretus hexatrema and Haploblepharus edwardsii, may enter sheltered micro-habitats within the reef during day light hours. These findings have highlighted the complex patterns that have evolved within marine fish to allow multiple species to coexist and exploit productive reef ecosystems by partitioning resource use and activity patterns at day or night, between depth zones and habitat types.
- Full Text:
- Date Issued: 2017
- Authors: Juby, Roxanne
- Date: 2017
- Subjects: Reef fishes -- Effect of light on , Reef fishes -- South Africa , Underwater videography in wildlife monitoring -- South Africa -- Tsitsikamma
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/44827 , vital:25445
- Description: Distinct day-night changes in ambient light are recognised as an important driver of animal activity patterns, with predictable changes to the structure and composition of animal communities between day and night. While day-night variation in the structure of animal communities has been well researched for terrestrial organisms and shallow marine fish communities around the world, there has been limited research of this type conducted on South Africa’s rocky reef fish communities. Consequently, we have a poor understanding of how nocturnal reef fish communities are structured and the day-night activity patterns of species inhabiting both shallow (10-30m) and deep-aphotic (55-100m) reefs. This research was conducted at two warm-temperate South African rocky reefs situated in Algoa Bay. The importance of natural ambient light in shaping the distribution of reef fish communities at shallow and deep-aphotic reef sites was demonstrated using baited remote underwater stereo-video systems (stereo-BRUVs). Distinct day and night fish communities were sampled at shallow and deep-aphotic reef sites. These differences were driven by significant changes in species richness (p < 0.001), species abundance (p < 0.001) and community composition (p < 0.001). These shifts appeared to be driven by day-night activity patterns that were the result of increased detectability of certain species at either day or night. The majority of species belonging to the family Sparidae showed evidence of strict diurnal activity, with their activity being further restricted to shallow reefs. These species showed evidence that they may enter micro-habitats within the reef at night. Similar activity patterns were shown for other top predatory teleost species and low level consumers, with substantial reductions in abundances, or no recordings at night throughout this study. Shallow reefs at day harboured the most diverse fish community. It is therefore hypothesised that this habitat was associated with conditions that offered improved access to resources for many visual species. In addition, the diverse community inhabiting shallow reefs at day is associated with a high risk of negative interspecies interactions, such as competition and predation. It is hypothesised that the biotic conditions associated with shallow reefs at day drove three movement patterns identified in this study; Pagellus bellottii natalensis showed evidence of movement onto shallow reefs at night from adjacent sandy flats, while Pterogymnus laniarius and Squalus sp. 1 showed evidence of movement onto shallow reefs at night from the deep- aphotic reefs that remain dark throughout the diel cycle. It is further hypothesised that other species which showed evidence for nocturnal activity, i.e. Galeichthys ater, Eptatretus hexatrema and Haploblepharus edwardsii, may enter sheltered micro-habitats within the reef during day light hours. These findings have highlighted the complex patterns that have evolved within marine fish to allow multiple species to coexist and exploit productive reef ecosystems by partitioning resource use and activity patterns at day or night, between depth zones and habitat types.
- Full Text:
- Date Issued: 2017
Early stage ichthyofauna from shallow water habitats of the Angola-Benguela frontal zone
- Authors: Farthing, Matthew William
- Date: 2017
- Subjects: Fishes -- Larvae -- South Africa -- Atlantic coast , Fishes -- Larvae -- Angola -- Atlantic coast , Striped mullet -- Angola -- Atlantic coast
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50442 , vital:25988
- Description: Early stage fishes (larvae and early juveniles) were collected from an array of shallow water (±1.5m) habitats on the warm-temperate southern Angolan coastline between June 2014 and June 2015. This study, the first assessment of the early stages of coastal fishes in Angola, provides important new understanding of non-estuarine shallow water nursery habitat use by coastal fishes from the region. In total, 51 species from 18 teleost families were observed. The exposed surf zone was dominated by postflexion larvae, while the moderately exposed beach and sheltered bay were dominated by early juveniles. Both fish density and diversity peaked in the wet season (Feb – Apr 2015) for all habitats, attributed to the influx of summer spawning species. Diplodus sargus dominated catches from the exposed surf zone, and the timing of observations supports the growing consensus that sparid spawning is dictated by temperature, not season. The similitude of the observed species to those observed in warm temperate South Africa highlights the historical connection of the warm-temperate study area with warm-temperate South Africa, prior to the formation of the Benguela Current as a vicariant barrier. The classification of the study assemblage into established estuarine utilization categories showed that the surf zone hosted more exclusively marine species than comparable surf zones in South Africa, attributed to the absence of estuaries in southern Angola. However, the observation of the marine estuarine dependent Mugil cephalus in this study area devoid of estuaries suggests that estuarine dependency may be regionally specific for some taxa. It appears that the warm, sheltered, nutrient rich waters of Tombua Bay provide typically estuarine associated taxa with a suitable alternative, non-estuarine nursery habitat. This study provides evidence that the importance of estuaries as critical nursery habitats has been overemphasized for some warm-temperate coastal fishes. However, the absence of other marine estuarine dependent species from the study area suggests that some warm-temperate taxa do intrinsically rely on estuarine function for survival.
- Full Text:
- Date Issued: 2017
- Authors: Farthing, Matthew William
- Date: 2017
- Subjects: Fishes -- Larvae -- South Africa -- Atlantic coast , Fishes -- Larvae -- Angola -- Atlantic coast , Striped mullet -- Angola -- Atlantic coast
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/50442 , vital:25988
- Description: Early stage fishes (larvae and early juveniles) were collected from an array of shallow water (±1.5m) habitats on the warm-temperate southern Angolan coastline between June 2014 and June 2015. This study, the first assessment of the early stages of coastal fishes in Angola, provides important new understanding of non-estuarine shallow water nursery habitat use by coastal fishes from the region. In total, 51 species from 18 teleost families were observed. The exposed surf zone was dominated by postflexion larvae, while the moderately exposed beach and sheltered bay were dominated by early juveniles. Both fish density and diversity peaked in the wet season (Feb – Apr 2015) for all habitats, attributed to the influx of summer spawning species. Diplodus sargus dominated catches from the exposed surf zone, and the timing of observations supports the growing consensus that sparid spawning is dictated by temperature, not season. The similitude of the observed species to those observed in warm temperate South Africa highlights the historical connection of the warm-temperate study area with warm-temperate South Africa, prior to the formation of the Benguela Current as a vicariant barrier. The classification of the study assemblage into established estuarine utilization categories showed that the surf zone hosted more exclusively marine species than comparable surf zones in South Africa, attributed to the absence of estuaries in southern Angola. However, the observation of the marine estuarine dependent Mugil cephalus in this study area devoid of estuaries suggests that estuarine dependency may be regionally specific for some taxa. It appears that the warm, sheltered, nutrient rich waters of Tombua Bay provide typically estuarine associated taxa with a suitable alternative, non-estuarine nursery habitat. This study provides evidence that the importance of estuaries as critical nursery habitats has been overemphasized for some warm-temperate coastal fishes. However, the absence of other marine estuarine dependent species from the study area suggests that some warm-temperate taxa do intrinsically rely on estuarine function for survival.
- Full Text:
- Date Issued: 2017