The effect of habitat and spatial management on reef fish in an established marine protected area
- Authors: Dames, Vivienne Abigail
- Date: 2021
- Subjects: iSimangaliso Wetland Park (South Africa) -- Management , Reef fishes -- South Africa -- KwaZulu-Natal , Baited remote underwater stereo-video systems (stereo-BRUVs) , Marine parks and reserves -- Monitoring -- South Africa -- KwaZulu-Natal , Fish populations -- Measurement
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/171150 , vital:42024
- Description: The persistence of harvested fish populations in the Anthropocene will be determined, above all, by how they respond to the interacting effects of climate change and fisheries exploitation. Predicting how populations will respond to both these threats is essential for any adaptive and sustainable management strategy. The response of fish populations to climate change is underpinned by physiological rates and tolerances, and emerging evidence suggests there may be physiological-based selection in capture fisheries. By quantifying important physiological rates of a model species, the endemic seabream, Chrysoblephus laticeps, across ecologically relevant thermal gradients and from populations subjected to varying intensities of commercial exploitation, this thesis aimed to 1) provide the first physiologically grounded climate resilience assessment for a South African linefish species, and 2) elucidate whether exploitation can drive populations to less physiologically resilient states in response to climate change. To identify physiologically limiting sea temperatures and to determine if exploitation alters physiological trait distributions, an intermittent flow respirometry experiment was used to test the metabolic response of spatially protected and exploited populations of C. laticeps to acute thermal variability. Exploited populations showed reduced metabolic phenotype diversity, fewer high-performance aerobic scope phenotypes, and a significantly lower aerobic scope curve across all test temperatures. Although both populations maintained a relatively high aerobic scope across a wide thermal range, their metabolic rates were compromised when extreme cold events were simulated (8 °C), suggesting that predicted future increases in upwelling frequency and intensity may be the primary limiting factor in a more thermally variable future ocean. The increment widths of annuli in the otoliths of C. laticeps from contemporary and historic collections were measured, as a proxy for the annual growth rate of exploited and protected populations. Hierarchical mixed models were used to partition growth variation within and among individuals and ascribe growth to intrinsic and extrinsic effects. The best model for the protected population indicated that the growth response of C. laticeps was poorer during years characterised by a high cumulative upwelling intensity, and better during years characterised by higher mean autumn sea surface temperatures. The exploited population growth chronology was too short to identify an extrinsic growth driver. The growth results again highlight the role of thermal variability in modulating the response of C. laticeps to its ambient environment and indicate that the predicted increases in upwelling frequency and intensity may constrain future growth rates of this species. A metabolic index (ϕ), representing the ratio of O2 supply to demand at various temperatures and oxygen concentrations, was estimated for exploited and protected populations of C. laticeps and used to predict future distribution responses. There was no difference in the laboratory calibrations of ϕ between populations, and all data was subsequently combined into a single piecewise (12 °C) calibrated ϕ model. To predict the distribution of C. laticeps, ϕ was projected across a high-resolution ocean model of the South African coastal zone, and a species distribution model implemented using the random forest algorithm and C. laticeps occurrence points. The future distribution of C. laticeps was estimated by predicting trained models across ocean model projections up to 2100. The best predictor of C. laticeps’ current distribution was minimum monthly ϕ and future predictions indicated only a slight range contraction on either edge of C. laticeps’ distribution by 2100. In order to provide policy makers, currently developing climate change management frameworks for South Africa’s ocean, with a usable output, the results of all research chapters were combined into a marine spatial model. The spatial model identified areas where C. laticeps is predicted to be resilient to climate change in terms of physiology, growth and distribution responses, which can then be prioritised for adaptation measures, such as spatial protection from exploitation. While these results are specific to C. laticeps, the methodology developed to identify areas of climate resilience has broad applications across taxa. From a global perspective, perhaps the most salient points to consider from this case study are the evidence of selective exploitation on physiological traits and the importance of environmental variability, rather than long-term mean climate changes, in affecting organism performance. These ideas are congruent with the current paradigm shift in how we think of the ocean, selective fisheries, and how they relate to organism climate resilience.
- Full Text:
- Date Issued: 2021
- Authors: Dames, Vivienne Abigail
- Date: 2021
- Subjects: iSimangaliso Wetland Park (South Africa) -- Management , Reef fishes -- South Africa -- KwaZulu-Natal , Baited remote underwater stereo-video systems (stereo-BRUVs) , Marine parks and reserves -- Monitoring -- South Africa -- KwaZulu-Natal , Fish populations -- Measurement
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/171150 , vital:42024
- Description: The persistence of harvested fish populations in the Anthropocene will be determined, above all, by how they respond to the interacting effects of climate change and fisheries exploitation. Predicting how populations will respond to both these threats is essential for any adaptive and sustainable management strategy. The response of fish populations to climate change is underpinned by physiological rates and tolerances, and emerging evidence suggests there may be physiological-based selection in capture fisheries. By quantifying important physiological rates of a model species, the endemic seabream, Chrysoblephus laticeps, across ecologically relevant thermal gradients and from populations subjected to varying intensities of commercial exploitation, this thesis aimed to 1) provide the first physiologically grounded climate resilience assessment for a South African linefish species, and 2) elucidate whether exploitation can drive populations to less physiologically resilient states in response to climate change. To identify physiologically limiting sea temperatures and to determine if exploitation alters physiological trait distributions, an intermittent flow respirometry experiment was used to test the metabolic response of spatially protected and exploited populations of C. laticeps to acute thermal variability. Exploited populations showed reduced metabolic phenotype diversity, fewer high-performance aerobic scope phenotypes, and a significantly lower aerobic scope curve across all test temperatures. Although both populations maintained a relatively high aerobic scope across a wide thermal range, their metabolic rates were compromised when extreme cold events were simulated (8 °C), suggesting that predicted future increases in upwelling frequency and intensity may be the primary limiting factor in a more thermally variable future ocean. The increment widths of annuli in the otoliths of C. laticeps from contemporary and historic collections were measured, as a proxy for the annual growth rate of exploited and protected populations. Hierarchical mixed models were used to partition growth variation within and among individuals and ascribe growth to intrinsic and extrinsic effects. The best model for the protected population indicated that the growth response of C. laticeps was poorer during years characterised by a high cumulative upwelling intensity, and better during years characterised by higher mean autumn sea surface temperatures. The exploited population growth chronology was too short to identify an extrinsic growth driver. The growth results again highlight the role of thermal variability in modulating the response of C. laticeps to its ambient environment and indicate that the predicted increases in upwelling frequency and intensity may constrain future growth rates of this species. A metabolic index (ϕ), representing the ratio of O2 supply to demand at various temperatures and oxygen concentrations, was estimated for exploited and protected populations of C. laticeps and used to predict future distribution responses. There was no difference in the laboratory calibrations of ϕ between populations, and all data was subsequently combined into a single piecewise (12 °C) calibrated ϕ model. To predict the distribution of C. laticeps, ϕ was projected across a high-resolution ocean model of the South African coastal zone, and a species distribution model implemented using the random forest algorithm and C. laticeps occurrence points. The future distribution of C. laticeps was estimated by predicting trained models across ocean model projections up to 2100. The best predictor of C. laticeps’ current distribution was minimum monthly ϕ and future predictions indicated only a slight range contraction on either edge of C. laticeps’ distribution by 2100. In order to provide policy makers, currently developing climate change management frameworks for South Africa’s ocean, with a usable output, the results of all research chapters were combined into a marine spatial model. The spatial model identified areas where C. laticeps is predicted to be resilient to climate change in terms of physiology, growth and distribution responses, which can then be prioritised for adaptation measures, such as spatial protection from exploitation. While these results are specific to C. laticeps, the methodology developed to identify areas of climate resilience has broad applications across taxa. From a global perspective, perhaps the most salient points to consider from this case study are the evidence of selective exploitation on physiological traits and the importance of environmental variability, rather than long-term mean climate changes, in affecting organism performance. These ideas are congruent with the current paradigm shift in how we think of the ocean, selective fisheries, and how they relate to organism climate resilience.
- Full Text:
- Date Issued: 2021
Towards the development of a pro-environmental strategy for improving catch-and-release behaviour in recreational fisheries – a case study on a competitive South African angling body
- Authors: Mannheim, Samantha L
- Date: 2021
- Subjects: Fishing -- Environmental aspects -- South Africa , Fishing -- South Africa , Fishers -- Attitudes -- South Africa , Fishers -- Attitudes -- South Africa -- Cast studies , Fishes -- Conservation -- South Africa , Rock and Surf Super Pro League , Southern African Fisheries Ecology Research Lab
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/171862 , vital:42133
- Description: Catch-and-release (C&R) is becoming increasingly popular in recreational fisheries with the potential to contribute towards conserving the oceans limited fish stocks. Several studies have highlighted high rates of mortality and many sub-lethal effects which ultimately have a negative impact on fish population viability. With poorly developed handling practices, the fish that are released suffer the consequences of physical and physiological stress and do not always survive, thus making the ethics of C&R fishing questionable. Many studies have contributed to our understanding of the factors that influence the fate of fish released by anglers. Despite this, few interventions have been able to improve angler C&R behaviour. Pro-environmental behavioural strategies however hold some potential for improving angler C&R behaviour. To test their potential, we partnered with the South African Rock and Surf Super Pro League (RASSPL Africa), the biggest exclusively C&R competitive shore-based angling league in South Africa. The first two years (2013 and 2014) of the partnership were purely focused on building trust and relationships and making observations on angler behaviour. In 2015, we collected baseline data on angler behaviour and fish health during the RASSPL national fishing competition. This was followed by comparable data collection at the following two national competitions in 2016 and 2017 after the introduction of a combination of pro- environmental behaviour interventions, including rule changes, improving angler knowledge, behavioural modelling, rewards, penalties and feedback to improve C&R behaviour. There were significant improvements in angler behaviour, including a decline in total air exposure from 101.93s ± 64.34 in 2015 to 77.37s ± 60.52 in 2017 (F(2,618) = 9.27, P < 0.01), and the time taken for an angler to place their fish into a bucket declined from 105.86s ± 69.47 in 2015 to 23.05s ± 24.13 in 2017 (F(2,556) = 158.71, P < 0.01). There were also improvements in the health of the fish, with a decline in the blood lactate concentration and mean reflex action mortality predictor (RAMP’s) scores for the dominant species, Diplodus capensis (lactate – 9.46 ± 3.80 mmol.l-1 in 2015 and 6.69 ± 2.99 mmol.l-1 in 2017, RAMP – 0.28 ± 0.22 in 2015 and 0.19 ± 0.17 in 2017), and Haploblapharus fuscus (lactate – 4.25 ± 1.89 mmol.l-1 in 2015 and 1.76 ± 0.78 mmol.l-1in 2017, RAMP – 0.15 ± 0.18 in 2015 and 0 ± 0 in 2017). In 2018, surveys were conducted to gain insight into angler demographics and external (social, economic, cultural and institutional) and internal factors (knowledge and awareness, motivations, attitudes and perceptions) associated with the RASSPL anglers. Surveys were also designed to assist in identifying what components were key drivers behind the angler’s behavioural changes. The demographic characteristics of RASSPL anglers were not dissimilar from the general recreational angling public in South Africa, suggesting that this kind of intervention may have potential at a broader scale. In terms of the drivers of behavioural change, the surveys revealed that 68% of respondents strongly agreed that the structural rule changes contributed to their improved behaviour. This was followed by the educational presentations (66% of the respondents) and modelling / demonstrative videos (59% of the respondents). The conservation prizes were considered less effective, with only 27% of anglers strongly agreeing that this intervention improved their C&R behaviour. Overall this study has demonstrated that it is possible to improve the C&R behaviour of anglers in a competitive setting, with the most effective component of the intervention being the use of rule changes (structural approach). These findings suggest that proenvironmental strategies hold potential for improving the C&R behaviour of anglers and the health of released fishes. It is suggested that interventions to improve C&R behaviour should aim to develop long-term relationships, and implement a broad range of well communicated strategies based on reliable data and sound rationality. Key words: marine shore-based fisheries; community engagement; pro- environmental behaviour; behavioural intervention.
- Full Text:
- Date Issued: 2021
- Authors: Mannheim, Samantha L
- Date: 2021
- Subjects: Fishing -- Environmental aspects -- South Africa , Fishing -- South Africa , Fishers -- Attitudes -- South Africa , Fishers -- Attitudes -- South Africa -- Cast studies , Fishes -- Conservation -- South Africa , Rock and Surf Super Pro League , Southern African Fisheries Ecology Research Lab
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/171862 , vital:42133
- Description: Catch-and-release (C&R) is becoming increasingly popular in recreational fisheries with the potential to contribute towards conserving the oceans limited fish stocks. Several studies have highlighted high rates of mortality and many sub-lethal effects which ultimately have a negative impact on fish population viability. With poorly developed handling practices, the fish that are released suffer the consequences of physical and physiological stress and do not always survive, thus making the ethics of C&R fishing questionable. Many studies have contributed to our understanding of the factors that influence the fate of fish released by anglers. Despite this, few interventions have been able to improve angler C&R behaviour. Pro-environmental behavioural strategies however hold some potential for improving angler C&R behaviour. To test their potential, we partnered with the South African Rock and Surf Super Pro League (RASSPL Africa), the biggest exclusively C&R competitive shore-based angling league in South Africa. The first two years (2013 and 2014) of the partnership were purely focused on building trust and relationships and making observations on angler behaviour. In 2015, we collected baseline data on angler behaviour and fish health during the RASSPL national fishing competition. This was followed by comparable data collection at the following two national competitions in 2016 and 2017 after the introduction of a combination of pro- environmental behaviour interventions, including rule changes, improving angler knowledge, behavioural modelling, rewards, penalties and feedback to improve C&R behaviour. There were significant improvements in angler behaviour, including a decline in total air exposure from 101.93s ± 64.34 in 2015 to 77.37s ± 60.52 in 2017 (F(2,618) = 9.27, P < 0.01), and the time taken for an angler to place their fish into a bucket declined from 105.86s ± 69.47 in 2015 to 23.05s ± 24.13 in 2017 (F(2,556) = 158.71, P < 0.01). There were also improvements in the health of the fish, with a decline in the blood lactate concentration and mean reflex action mortality predictor (RAMP’s) scores for the dominant species, Diplodus capensis (lactate – 9.46 ± 3.80 mmol.l-1 in 2015 and 6.69 ± 2.99 mmol.l-1 in 2017, RAMP – 0.28 ± 0.22 in 2015 and 0.19 ± 0.17 in 2017), and Haploblapharus fuscus (lactate – 4.25 ± 1.89 mmol.l-1 in 2015 and 1.76 ± 0.78 mmol.l-1in 2017, RAMP – 0.15 ± 0.18 in 2015 and 0 ± 0 in 2017). In 2018, surveys were conducted to gain insight into angler demographics and external (social, economic, cultural and institutional) and internal factors (knowledge and awareness, motivations, attitudes and perceptions) associated with the RASSPL anglers. Surveys were also designed to assist in identifying what components were key drivers behind the angler’s behavioural changes. The demographic characteristics of RASSPL anglers were not dissimilar from the general recreational angling public in South Africa, suggesting that this kind of intervention may have potential at a broader scale. In terms of the drivers of behavioural change, the surveys revealed that 68% of respondents strongly agreed that the structural rule changes contributed to their improved behaviour. This was followed by the educational presentations (66% of the respondents) and modelling / demonstrative videos (59% of the respondents). The conservation prizes were considered less effective, with only 27% of anglers strongly agreeing that this intervention improved their C&R behaviour. Overall this study has demonstrated that it is possible to improve the C&R behaviour of anglers in a competitive setting, with the most effective component of the intervention being the use of rule changes (structural approach). These findings suggest that proenvironmental strategies hold potential for improving the C&R behaviour of anglers and the health of released fishes. It is suggested that interventions to improve C&R behaviour should aim to develop long-term relationships, and implement a broad range of well communicated strategies based on reliable data and sound rationality. Key words: marine shore-based fisheries; community engagement; pro- environmental behaviour; behavioural intervention.
- Full Text:
- Date Issued: 2021
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