Towards a better understanding of small-scale fishing decisions and their consequences in Northern Mozambique
- Authors: Heckendorn, Katrina Ann
- Date: 2023-10-13
- Subjects: Fishery management Mozambique , Small-scale fisheries Mozambique , Collective action , Functional diversity , Fishes Effect of human beings on Mozambique , Socioecology
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/431797 , vital:72805 , DOI 10.21504/10962/431797
- Description: This study investigates the relationship between the interacting social and ecological systems within the Pemba Bay fishery, in Northern Mozambique, as mediated by fishing decisions. All ecosystems in the world are affected by human behaviours in some way. In many cases, human effects on ecosystems are detrimental to many other species and can cause shifts in the entire system. In fisheries, the connections between human behaviours and ecosystems are obvious, as fishers extract wild populations of marine species. Human behavioural plasticity and sometimes rapid cultural evolution allow human behaviours to change and adapt faster than many other species can respond which often allows fishers to overexploit marine ecosystems. Many fisheries in the world are fully, or over exploited. Managing these fisheries often focuses on changing those highly adaptable human behaviours. Fishers’ motivations for making different fishing decisions as well as attitudes towards the fishery can be used to understand human interactions with ecosystems when the dependence between the two is direct, as well as allowing managers to tailor interventions that account for fishers’ motivations and attitudes. Most fisheries’ management projects assume that behaviours are motivated by profit maximization. This study investigates this assumption by comparing the compatibility of interview responses and fishing behaviours with rational actor theory, which assumes profit maximization is the only goal. Responses are also compared with prospect theory, which emphasizes reliability of outcomes; descriptive norms, which focuses on social interactions; habitual behaviour, which assumes most decision are automatic based on habit; and theory of planned behaviour, which allows attitudes to be shaped by economic or non-economic motivations, as well as peer opinion and incorporates perceived behavioural control in making decisions. These behavioural theories span a variety of potential fisher motivations which could affect fishing decisions. The study then investigates the state of the social and ecological systems which have resulted, at least in part, from those fishing decisions, and makes recommendations on possible interventions to improve the system based on better understanding of fishers’ attitudes and motivations. The study tests the hypothesis that fishers are motivated primarily by profit maximization and, therefore, rational actor theory is most compatible with fishers’ stated motivations for fishing, or alternatively, that one of the other behavioural theories better explains fisher responses. This section used categorized interview responses based on their agreement, or not, with assumed responses if a particular behavioural theory were compatible. The results indicate that four of the five theories are most compatible with responses for at least one fisher, but that the theory of planned behaviour is the most consistent with the data overall, not rational actor theory. Specifically, fishers seem concerned with behavioural control as well as some non-catch related characteristics of the fishery, such as collective action and sustainability. The second hypothesis is that prospect theory is more compatible with current fishing behaviours than rational actor theory. Prospect theory states that people prefer more reliable outcomes, even if slightly less profitable, than outcomes which are more profitable on average, but also more variable. This section used catch data, and changes in relative use of different fishing methods to address this hypothesis. This hypothesis is confirmed for some aspects of fishery data, but not all. Fishers prefer methods which are more reliable and these methods are increasing in relative use. However, neither catch value nor reliability increases fishers’ opinions of their fishing method, but fisher characteristics which increase options do. This again indicates that behavioural control is important in determining fishers’ attitudes towards fishing. The third question addresses the social system within the fishery. It investigates whether fishing in Pemba Bay is a chosen profession or a livelihood of desperation from the poorest individuals. The study hypothesizes that fishers are as well-off as their non-fishing neighbours, and fishers who use more reliable or profitable methods are better off than those using less reliable/profitable methods and, as such, are more committed to fishing as a way of life. This section used fisher interview responses and household surveys to compare subjective and material wellbeing of fishers and non-fishers around Pemba Bay. The first part of the hypothesis is partly supported. Fishers using most methods have material standards of living comparable to non-fishers. However, they report lower subjective well-beings. Most measures of wellbeing are not affected by the reliability or profitability of the fishing method used, which does not support the second part of the hypothesis. Additionally, fishers using more profitable or reliable methods do not indicate more commitment to fishing as a way of life. The fourth and final section investigates the marine ecosystem. Based on conversations with fishers and local researchers, it is assumed that the Pemba fishery is overexploited. As such, the study hypothesizes that marine biomass, individual size of marine species, and functional diversity are lower in Pemba Bay than in other sites around Northern Mozambique, Vamizi Island, Situ Island, and Nuarro, due to high fishing pressure, and that direct removal of species by fishing has a dominant effect. This final section used baited remote underwater videos (BRUVs) to compare species composition and indices of abundance from the different locations. Again, there is support for part of this hypothesis. Marine species biomass and sizes are lower in Pemba Bay than other sites in Northern Mozambique; however, functional diversity is not different. In these data, changes in biomass and size are not correlated with amount of catch, so direct removal by fishing may not be the dominant source of change in the Pemba fishery. Together, these data indicate that the Pemba fishery may be unsustainable based on social and ecological indications. The importance of behavioural control in understanding fishing decisions indicates that any interventions to mitigate problems in the fishery will need to work with fishers to increase empowerment and allow experimentation to find locally relevant solutions to problems. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-10-13
- Authors: Heckendorn, Katrina Ann
- Date: 2023-10-13
- Subjects: Fishery management Mozambique , Small-scale fisheries Mozambique , Collective action , Functional diversity , Fishes Effect of human beings on Mozambique , Socioecology
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/431797 , vital:72805 , DOI 10.21504/10962/431797
- Description: This study investigates the relationship between the interacting social and ecological systems within the Pemba Bay fishery, in Northern Mozambique, as mediated by fishing decisions. All ecosystems in the world are affected by human behaviours in some way. In many cases, human effects on ecosystems are detrimental to many other species and can cause shifts in the entire system. In fisheries, the connections between human behaviours and ecosystems are obvious, as fishers extract wild populations of marine species. Human behavioural plasticity and sometimes rapid cultural evolution allow human behaviours to change and adapt faster than many other species can respond which often allows fishers to overexploit marine ecosystems. Many fisheries in the world are fully, or over exploited. Managing these fisheries often focuses on changing those highly adaptable human behaviours. Fishers’ motivations for making different fishing decisions as well as attitudes towards the fishery can be used to understand human interactions with ecosystems when the dependence between the two is direct, as well as allowing managers to tailor interventions that account for fishers’ motivations and attitudes. Most fisheries’ management projects assume that behaviours are motivated by profit maximization. This study investigates this assumption by comparing the compatibility of interview responses and fishing behaviours with rational actor theory, which assumes profit maximization is the only goal. Responses are also compared with prospect theory, which emphasizes reliability of outcomes; descriptive norms, which focuses on social interactions; habitual behaviour, which assumes most decision are automatic based on habit; and theory of planned behaviour, which allows attitudes to be shaped by economic or non-economic motivations, as well as peer opinion and incorporates perceived behavioural control in making decisions. These behavioural theories span a variety of potential fisher motivations which could affect fishing decisions. The study then investigates the state of the social and ecological systems which have resulted, at least in part, from those fishing decisions, and makes recommendations on possible interventions to improve the system based on better understanding of fishers’ attitudes and motivations. The study tests the hypothesis that fishers are motivated primarily by profit maximization and, therefore, rational actor theory is most compatible with fishers’ stated motivations for fishing, or alternatively, that one of the other behavioural theories better explains fisher responses. This section used categorized interview responses based on their agreement, or not, with assumed responses if a particular behavioural theory were compatible. The results indicate that four of the five theories are most compatible with responses for at least one fisher, but that the theory of planned behaviour is the most consistent with the data overall, not rational actor theory. Specifically, fishers seem concerned with behavioural control as well as some non-catch related characteristics of the fishery, such as collective action and sustainability. The second hypothesis is that prospect theory is more compatible with current fishing behaviours than rational actor theory. Prospect theory states that people prefer more reliable outcomes, even if slightly less profitable, than outcomes which are more profitable on average, but also more variable. This section used catch data, and changes in relative use of different fishing methods to address this hypothesis. This hypothesis is confirmed for some aspects of fishery data, but not all. Fishers prefer methods which are more reliable and these methods are increasing in relative use. However, neither catch value nor reliability increases fishers’ opinions of their fishing method, but fisher characteristics which increase options do. This again indicates that behavioural control is important in determining fishers’ attitudes towards fishing. The third question addresses the social system within the fishery. It investigates whether fishing in Pemba Bay is a chosen profession or a livelihood of desperation from the poorest individuals. The study hypothesizes that fishers are as well-off as their non-fishing neighbours, and fishers who use more reliable or profitable methods are better off than those using less reliable/profitable methods and, as such, are more committed to fishing as a way of life. This section used fisher interview responses and household surveys to compare subjective and material wellbeing of fishers and non-fishers around Pemba Bay. The first part of the hypothesis is partly supported. Fishers using most methods have material standards of living comparable to non-fishers. However, they report lower subjective well-beings. Most measures of wellbeing are not affected by the reliability or profitability of the fishing method used, which does not support the second part of the hypothesis. Additionally, fishers using more profitable or reliable methods do not indicate more commitment to fishing as a way of life. The fourth and final section investigates the marine ecosystem. Based on conversations with fishers and local researchers, it is assumed that the Pemba fishery is overexploited. As such, the study hypothesizes that marine biomass, individual size of marine species, and functional diversity are lower in Pemba Bay than in other sites around Northern Mozambique, Vamizi Island, Situ Island, and Nuarro, due to high fishing pressure, and that direct removal of species by fishing has a dominant effect. This final section used baited remote underwater videos (BRUVs) to compare species composition and indices of abundance from the different locations. Again, there is support for part of this hypothesis. Marine species biomass and sizes are lower in Pemba Bay than other sites in Northern Mozambique; however, functional diversity is not different. In these data, changes in biomass and size are not correlated with amount of catch, so direct removal by fishing may not be the dominant source of change in the Pemba fishery. Together, these data indicate that the Pemba fishery may be unsustainable based on social and ecological indications. The importance of behavioural control in understanding fishing decisions indicates that any interventions to mitigate problems in the fishery will need to work with fishers to increase empowerment and allow experimentation to find locally relevant solutions to problems. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-10-13
Long-term trends in fish length-at-age, catch-at-length and condition of the Namibian and South African commercially exploited species
- Authors: Iyambo, Elago Martha
- Date: 2022-10-14
- Subjects: Fishery management South Africa , Fishery management Namibia , Fishes Growth , Fisheries Fishing effort , Climatic changes , Fishes Climatic factors
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362872 , vital:65370
- Description: Fish growth rate is a flexible trait that can evolve in response to fishing or environmental change. Therefore, knowledge of fish growth rate patterns, long-term and short-term responses to fishing effort and environmental change is important for fisheries management in the Benguela. Historical and current age length keys have been used as indicators of annual fish growth in the Benguela, the growth rate study on Merluccius paradoxus demonstrated long-term changes in growth over three decades as a response to fishing. However, the fish growth rate patterns, in relation to fishing effort and environmental change patterns are still not known for the many commercially important stocks in the Benguela. The specific objectives of the project were to determine the annual variability and long-term trends, in annual mean lengths-at-age, catch-at-length and fish condition of 17 commercially exploited resources, targeted and bycatch in Namibia and South Africa in relation to environmental changes (sea surface temperature). The results showed that there was a significant decrease in mean length at age 7 for Merluccius capensis (Namibian stock), a significant decrease in mean length at ages 3 to 7 for South African M. capensis and a significant increase in mean length at ages 2 to 6 for South African M. paradoxus Fishery-induced evolution may be the reason for the increase in mean length in the early stages of hake. A regime shift was detected in the mean length at age 1 for Etrumeus whiteheadi (South African stock) caused by changes in water temperatures. A decrease in mean length of the catch was observed for Namibian M. capensis and the reason for this could have been the stock being overexploited during the years of the observed trend (1968 to 1987). Historically both the Namibian Lophius vomerinus and Helicolenus dactylopterus were bycatch of the hake fishery, therefore, the decrease in their mean length of the catch may be due to increased bycatch mortalities due to increased hake catches. The improvement in the management measures of the Jasus lalandii fishery and possible favourable oxygen fluctuation might have caused the stock to increase in mean length of the catch between 1977 and 1982. Fish condition showed a significant difference in stocks between years. Fish condition of M. capensis, M. paradoxus and T. capensis were analysed. The rest of the commercial stocks were omitted because there was limited length-weight data. For Namibian M. capensis the spawning season may have caused fish to have the best condition in 1987 and while higher temperatures in 1983 may have led to the worst condition in 1983. Higher prey availability in 1979 for Namibian M. paradoxus could have been the reason for fish with best condition being found in 1979. T. capensis had the highest condition index in 1986 when cooler summer SST prevailed that may have been more favourable for T. capensis to live in. July, September and January SSTs were significantly negatively correlated with the mean length of M. capensis at age 3. This was perhaps due to upwelling intensity and plankton productivity which increases in winter and decreases in summer. A separate study of the impacts of fishery-induced changes and density-dependence on fish growth rate, as well as the effects of other environmental variables is recommended. Since data for some species was outdated, it is suggested to update biological variables and assessment for future work. This study can be used to understand the key life history characteristics of Namibian and South African exploited resources, targeted and bycatch. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Iyambo, Elago Martha
- Date: 2022-10-14
- Subjects: Fishery management South Africa , Fishery management Namibia , Fishes Growth , Fisheries Fishing effort , Climatic changes , Fishes Climatic factors
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362872 , vital:65370
- Description: Fish growth rate is a flexible trait that can evolve in response to fishing or environmental change. Therefore, knowledge of fish growth rate patterns, long-term and short-term responses to fishing effort and environmental change is important for fisheries management in the Benguela. Historical and current age length keys have been used as indicators of annual fish growth in the Benguela, the growth rate study on Merluccius paradoxus demonstrated long-term changes in growth over three decades as a response to fishing. However, the fish growth rate patterns, in relation to fishing effort and environmental change patterns are still not known for the many commercially important stocks in the Benguela. The specific objectives of the project were to determine the annual variability and long-term trends, in annual mean lengths-at-age, catch-at-length and fish condition of 17 commercially exploited resources, targeted and bycatch in Namibia and South Africa in relation to environmental changes (sea surface temperature). The results showed that there was a significant decrease in mean length at age 7 for Merluccius capensis (Namibian stock), a significant decrease in mean length at ages 3 to 7 for South African M. capensis and a significant increase in mean length at ages 2 to 6 for South African M. paradoxus Fishery-induced evolution may be the reason for the increase in mean length in the early stages of hake. A regime shift was detected in the mean length at age 1 for Etrumeus whiteheadi (South African stock) caused by changes in water temperatures. A decrease in mean length of the catch was observed for Namibian M. capensis and the reason for this could have been the stock being overexploited during the years of the observed trend (1968 to 1987). Historically both the Namibian Lophius vomerinus and Helicolenus dactylopterus were bycatch of the hake fishery, therefore, the decrease in their mean length of the catch may be due to increased bycatch mortalities due to increased hake catches. The improvement in the management measures of the Jasus lalandii fishery and possible favourable oxygen fluctuation might have caused the stock to increase in mean length of the catch between 1977 and 1982. Fish condition showed a significant difference in stocks between years. Fish condition of M. capensis, M. paradoxus and T. capensis were analysed. The rest of the commercial stocks were omitted because there was limited length-weight data. For Namibian M. capensis the spawning season may have caused fish to have the best condition in 1987 and while higher temperatures in 1983 may have led to the worst condition in 1983. Higher prey availability in 1979 for Namibian M. paradoxus could have been the reason for fish with best condition being found in 1979. T. capensis had the highest condition index in 1986 when cooler summer SST prevailed that may have been more favourable for T. capensis to live in. July, September and January SSTs were significantly negatively correlated with the mean length of M. capensis at age 3. This was perhaps due to upwelling intensity and plankton productivity which increases in winter and decreases in summer. A separate study of the impacts of fishery-induced changes and density-dependence on fish growth rate, as well as the effects of other environmental variables is recommended. Since data for some species was outdated, it is suggested to update biological variables and assessment for future work. This study can be used to understand the key life history characteristics of Namibian and South African exploited resources, targeted and bycatch. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
Stock structure of Patagonian toothfish Dissostichus eleginoides (Smitt 1898, family Nototheniidae) in the Southwest Atlantic
- Authors: Lee, Brendon
- Date: 2022-10-14
- Subjects: Otoliths , Patagonian toothfish Geographical distribution , Fish tagging , Biogeography , Microstructure , Microchemistry
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365599 , vital:65763 , DOI https://doi.org/10.21504/10962/365599
- Description: The identification of discrete self-sustaining productive units in marine populations is essential for achieving sustainable fisheries objectives. Marine fish populations frequently exhibit dynamic characteristics across their life-histories, displaying variability in spatial structure and mixing patterns, both within and among populations. The incoherent application of management boundaries on biological populations can bias stock assessment results and have important implications on sustainable fisheries management. Patagonian toothfish (Dissostichus eleginoides) is a long-lived, slow-growing, late-maturing, deep-sea, benthopelagic species. It forms the basis of important and highly lucrative industrial and artisanal fisheries across its distribution. Patagonian toothfish have complex life-histories characterised by high dispersal potential during the egg and larval phase, a wide depth range because of their ontogenetic migratory behaviour, and large adult size that is capable of undertaking long-distance active movements (>200 km). These characteristics provide opportunities for high levels of connectivity, and as such, the stock structure is not well understood. We applied an integrated, multidisciplinary approach to provide an improved understanding of the complex stock structure dynamics for Patagonian toothfish on the Patagonian Shelf, specifically in relation to the shelf, slope, and deep-sea plains around the Falkland Islands. Research results were focused on aspects pertaining to (1) geographic variation in phenotypic characters (otolith shape); (2) a description of the spatial-temporal distribution patterns; (3) the active movements of deep-sea adults (tag-recapture study); and (4) the identification of early life-history dispersal through otolith microstructure and microchemical chronologies. Results from the study indicate high regional connectivity during the early life-history stages derived from at least two spawning contingents into spatially discrete nursery areas (cohort groups) on the Falklands Shelf. Fish followed distinct ontogenetic pathways into deeper waters adjacent to the areas wherein juvenile settlement into a demersal habitat occurred. There is little to no evidence of mixing among cohort groups during their ontogenetic migration into deep-sea adult habitats, reflecting a mixed population based on oceanographically defined egg and larval dispersal. The majority of the adult component of the population continue to display high site fidelity. However, between 9 and 25% of the population, consisting predominantly of larger reproductively capable adults undertake long-distance dispersal behaviour, identified as home-range relocations from the adult deep-sea habitats towards three of the known southern spawning grounds in the region. Results are suggestive of a requirement for improved collaborative efforts for regionally-based management approaches with careful consideration of local stock contingents. Future monitoring and research priorities should focus on the identification of reproductive potential, dispersal pathways and settlement patterns of stock contingents to inform the dynamics of mixed stock origins across the Patagonian region. While many aspects regarding the stock structure remain unresolved, results derived from the current studies can be used to inform the development of management measures to ensure the continued recovery and sustainable management of Patagonian toothfish within the region. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Lee, Brendon
- Date: 2022-10-14
- Subjects: Otoliths , Patagonian toothfish Geographical distribution , Fish tagging , Biogeography , Microstructure , Microchemistry
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365599 , vital:65763 , DOI https://doi.org/10.21504/10962/365599
- Description: The identification of discrete self-sustaining productive units in marine populations is essential for achieving sustainable fisheries objectives. Marine fish populations frequently exhibit dynamic characteristics across their life-histories, displaying variability in spatial structure and mixing patterns, both within and among populations. The incoherent application of management boundaries on biological populations can bias stock assessment results and have important implications on sustainable fisheries management. Patagonian toothfish (Dissostichus eleginoides) is a long-lived, slow-growing, late-maturing, deep-sea, benthopelagic species. It forms the basis of important and highly lucrative industrial and artisanal fisheries across its distribution. Patagonian toothfish have complex life-histories characterised by high dispersal potential during the egg and larval phase, a wide depth range because of their ontogenetic migratory behaviour, and large adult size that is capable of undertaking long-distance active movements (>200 km). These characteristics provide opportunities for high levels of connectivity, and as such, the stock structure is not well understood. We applied an integrated, multidisciplinary approach to provide an improved understanding of the complex stock structure dynamics for Patagonian toothfish on the Patagonian Shelf, specifically in relation to the shelf, slope, and deep-sea plains around the Falkland Islands. Research results were focused on aspects pertaining to (1) geographic variation in phenotypic characters (otolith shape); (2) a description of the spatial-temporal distribution patterns; (3) the active movements of deep-sea adults (tag-recapture study); and (4) the identification of early life-history dispersal through otolith microstructure and microchemical chronologies. Results from the study indicate high regional connectivity during the early life-history stages derived from at least two spawning contingents into spatially discrete nursery areas (cohort groups) on the Falklands Shelf. Fish followed distinct ontogenetic pathways into deeper waters adjacent to the areas wherein juvenile settlement into a demersal habitat occurred. There is little to no evidence of mixing among cohort groups during their ontogenetic migration into deep-sea adult habitats, reflecting a mixed population based on oceanographically defined egg and larval dispersal. The majority of the adult component of the population continue to display high site fidelity. However, between 9 and 25% of the population, consisting predominantly of larger reproductively capable adults undertake long-distance dispersal behaviour, identified as home-range relocations from the adult deep-sea habitats towards three of the known southern spawning grounds in the region. Results are suggestive of a requirement for improved collaborative efforts for regionally-based management approaches with careful consideration of local stock contingents. Future monitoring and research priorities should focus on the identification of reproductive potential, dispersal pathways and settlement patterns of stock contingents to inform the dynamics of mixed stock origins across the Patagonian region. While many aspects regarding the stock structure remain unresolved, results derived from the current studies can be used to inform the development of management measures to ensure the continued recovery and sustainable management of Patagonian toothfish within the region. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
Towards an improved understanding of episodic benthic turbidity events (Benthic Nepheloid Layer) on the Eastern Agulhas Bank, South Africa
- Authors: Johnstone, Brett Mordaunt
- Date: 2022-10-14
- Subjects: Nepheloid layer , Turbidity , Loligo reynaudii , Fisheries South Africa , Oceanography , Remote sensing , Altimetry , Climatic changes
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362883 , vital:65371
- Description: The harvest of Loligo reynaudii, or "chokka," represents a critical source of revenue and job creation in the historically impoverished Eastern Cape Province of South Africa. Due to the importance of visual stimuli in the reproductive processes, it has been hypothesized that a primary driver of successful reproduction is the clarity of the water column. The presence of increased particulate matter concentrations within the water column generates turbid conditions near the seafloor (visibility < 1m), that are proposed to restrict spawning activity. This benthic nepheloid layer (BNL) contains both organic and inorganic components, with the BNL intensity a function of bottom turbulence, substratum type, and detritus level. However, the spatial and temporal resolution of BNL intensity on the Eastern Agulhas Bank (EAB) and the environmental drivers thereof remain unknown. Here we show that benthic turbidity events are a common but highly variable occurrence on the EAB. Results from a 17-month time-series of in-situ and remote sensing data between 2002 – 2004 in Algoa Bay, supplemented by experiments in other bays important for spawning, show that turbid conditions existed for ∼ 30 % of the sample period. Exploration of environmental drivers, including the influence of wind, altimeter-derived significant wave height (Hs), sea surface temperature (SST), and chlorophyll-a (Chl-a) concentrations indicate that BNL intensity does not conform to a "one-size-fits-all" approach. Rather, complex local hydrological and physiochemical parameters control the BNL characteristics on the EAB. Global warming is likely to increase the frequency and intensity of extreme westerly-wind and storm events, promoting BNL events on the Eastern Agulhas Bank and possibly causing a shift in the reproductive strategy of chokka squid to the cooler mid shelf region. This is likely to have consequences for both the species in terms of reproductive success and the fishery, which is concentrated on inshore spawning aggregations. Future research needs to quantify and characterize the constituents, source particles and spatial-temporal variability of BNL events in order to build a predictive capacity. Through incorporating the qualitative analysis of the dynamics of nepheloid layers on the EAB into Regional Oceanographic Models (ROMS), General Linear Models (GLM) and particle distribution models such as DELFT-3D, it is possible to move toward predicting the timing and intensity of these events. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Johnstone, Brett Mordaunt
- Date: 2022-10-14
- Subjects: Nepheloid layer , Turbidity , Loligo reynaudii , Fisheries South Africa , Oceanography , Remote sensing , Altimetry , Climatic changes
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362883 , vital:65371
- Description: The harvest of Loligo reynaudii, or "chokka," represents a critical source of revenue and job creation in the historically impoverished Eastern Cape Province of South Africa. Due to the importance of visual stimuli in the reproductive processes, it has been hypothesized that a primary driver of successful reproduction is the clarity of the water column. The presence of increased particulate matter concentrations within the water column generates turbid conditions near the seafloor (visibility < 1m), that are proposed to restrict spawning activity. This benthic nepheloid layer (BNL) contains both organic and inorganic components, with the BNL intensity a function of bottom turbulence, substratum type, and detritus level. However, the spatial and temporal resolution of BNL intensity on the Eastern Agulhas Bank (EAB) and the environmental drivers thereof remain unknown. Here we show that benthic turbidity events are a common but highly variable occurrence on the EAB. Results from a 17-month time-series of in-situ and remote sensing data between 2002 – 2004 in Algoa Bay, supplemented by experiments in other bays important for spawning, show that turbid conditions existed for ∼ 30 % of the sample period. Exploration of environmental drivers, including the influence of wind, altimeter-derived significant wave height (Hs), sea surface temperature (SST), and chlorophyll-a (Chl-a) concentrations indicate that BNL intensity does not conform to a "one-size-fits-all" approach. Rather, complex local hydrological and physiochemical parameters control the BNL characteristics on the EAB. Global warming is likely to increase the frequency and intensity of extreme westerly-wind and storm events, promoting BNL events on the Eastern Agulhas Bank and possibly causing a shift in the reproductive strategy of chokka squid to the cooler mid shelf region. This is likely to have consequences for both the species in terms of reproductive success and the fishery, which is concentrated on inshore spawning aggregations. Future research needs to quantify and characterize the constituents, source particles and spatial-temporal variability of BNL events in order to build a predictive capacity. Through incorporating the qualitative analysis of the dynamics of nepheloid layers on the EAB into Regional Oceanographic Models (ROMS), General Linear Models (GLM) and particle distribution models such as DELFT-3D, it is possible to move toward predicting the timing and intensity of these events. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
Baseline description of the Benthic Biotopes for two Long-Term Ecological Research (LTER) stations in Algoa Bay, Agulhas ecoregion, South Africa
- Authors: Parker-Nance, Shirley
- Date: 2021-10-29
- Subjects: Benthic ecology South Africa Algoa Bay , Long-Term Ecological Research Program , Marine invertebrates South Africa Algoa Bay , Reef ecology South Africa Algoa Bay , Coastal zone management South Africa Algoa Bay , Reef fishes South Africa Algoa Bay , Ecological mapping South Africa Algoa Bay
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191680 , vital:45147 , 10.21504/10962/191680
- Description: Shallow coastal marine ecosystems provide important resources to society but are increasingly under threat from anthropogenic impacts. These systems form an interface between land and sea, providing valuable resources. Global environmental change, overexploitation, habitat transformation, pollution and policies aimed at short-term socio-economic gains are driving the loss of natural resources, productivity and biodiversity. Consequently, a comprehensive and holistic understanding of the current and future states of marine ecosystems is essential. This requires insight into the processes involved in maintaining genetic, species, habitat, community and biotope diversity at an ecosystem level. An understanding of ecosystem processes and the ability to detect changes in biodiversity, biotopes, seascape composition and ecosystem functioning require observation made over time and space. In response to this need, Long-Term Ecological Research (LTER) programmes such as those established by the South African Environmental Observation Network (SAEON) supported by the Department of Science and Innovation’s (DSI) Shallow Marine and Coastal Research Infrastructure (SMCRI) collect long–term observational data from different environments and systems. This study aimed to evaluate data collected as part of the developmental phase of a newly established benthic research platform. The datasets constructed are used to develop a baseline description of the benthic biotopes of two study areas within Algoa Bay. It aimed to gain insight into the feasibility of the methods used and the value of the data and derived essential biological variables (EVB). Assessing the sustainability of the programme over time was done through a practical evaluation of the methodology to be used and the technical feasibility of data collection and analysis. It furthermore aimed to assess the data usefulness in describing biodiversity at various scales and its sensitivity in reporting change. This pilot study provides valuable insight into data collection methodologies and introduces new sampling platforms. The baseline dataset consisted of data collected during the first 18 months of the SAEON Benthic Ecosystem Long-Term Ecological Research (BELTER) platform in Algoa Bay, Agulhas ecoregion, Western Indian Ocean, South Africa. This comprised of the collection of images for 150 m2 of the researched benthic seascape and 306 stereo video data streams. The 77 760 point dataset allowed the identification of 12 substrate types, 7 biotopes, 44 sub-biotope units, 377 sessile and sedentary benthic species and 51 ichthyofauna species. The described habitat and benthic communities and the defined benthic biotopes allowed for the assessment of biotope heterogeneity and the construction of a provisional distribution map for the broader biotopes. This work includes a study into the infra- and supra-benthic ichthyofauna associated with the defined biotopes and investigates the role habitat and benthic communities play in the distribution of these fish 3 assemblages. Lastly, it assesses the value of morphological traits and diversity indices for describing and comparing abiotic and biotic components of observed systems within the shallow coastal marine seascape. This study shows that species composition differs significantly between biotopes with habitat type playing a key role in the composition of the benthos. Substrate type, consolidated or unconsolidated, depth and the composition of the soft sediment is the most important determining factors. The White Sands Reef station has a higher species diversity than the St Croix Island Complex station with a higher percentage cover associated with the hard substrate. The dissimilarity between biotopes and communities are generally high although similarity within the biotopes or communities was found to be relatively low. This was considered indicative of high heterogeneity within the biotopes and a patch or mosaic-like distribution of communities within the broader biotope. A fine-scale a posteriori analysis of the data collected confirmed the high heterogeneous nature of both habitat and communities within the broader biotope. The description of the abiotic and biotic variables resulted in the identification of a diverse suite of biotope subunits. The character of the biotope hinges not only on the composition of the substrate and biota present but the contribution of smaller distinct biotopes subunits, their distribution and representation within broader biotopes and the degree these are shared with other broader biotopes. The distribution of these biotope units at different scales is believed to be important in understanding inherent diversity, niche partitioning and connectivity within a highly heterogeneous seascape. Ichthyofauna associated with the broader biotopes were indicative of the substrate type. Low profile reef systems with interspaced sandy stretches supported both reef fish and those typically associated with sandy substrates. Benthic biotopes associated characteristically with higher profile reef systems and less sand or soft sediment were mainly utilized by reef-associated fish species. Substrate type, depth and seasonality were found to be important factors in the observed composition and distribution of ichthyofauna over the seascape. Although fish species were found to have a wide distribution and made use of multiple biotopes the average abundance of the species within the observed assemblages differed. Analysis of ichthyofauna species composition indicated that observed fish assemblages were homogeneous within five of the seven biotopes. Broader biotopes that were found to be significantly different between sample locations are characterised by a diverse complement of biotope subunits and are highly heterogeneous. Traits and diversity indices are important tools for assessing and comparing different systems within the seascape, both spatially and temporally. The classification of the biota into broader phylogenetic groups indicated a significant difference between biotopes. This is especially useful when detailed 4 analysis or species identification is not possible or the skill set is not available. Morphological traits included in this study informed on the physical structure of the communities present and in combination with substrate type provided insight into the three-dimensional structure of the biotope. Species diversity, abundance, density estimates and the Shannon-Weiner diversity index were found to be the most useful diversity indices characterising and comparing biotopes. This was less so for ichthyofauna. Significant differences in the number of species observed were evident only between consolidated and unconsolidated dominated substrates. Although there was no significant difference in the number of individuals observed, both the Shannon-Weiner and Simpson Diversity indices were able to highlight differences in the fish assemblages observed for the different biotopes. The data collected, although permitting a comprehensive baseline assessment of the benthic environment for two research stations within the SAEON Algoa Bay LTER Sentinel Site, is temporally limited. The ichthyofauna dataset used was small and it is understood that the addition of length-frequency analysis of observed ichthyofauna will benefit our understanding of the biotope use by infra- and supra-benthic fish species over their life history within the larger seascape. Seasonal differences were evident and it is expected that datasets spanning several years, including LTER stations within different marine ecosystems types, will provide valuable insights on system dynamics in the short and long term both spatially and temporally. This study is the first attempt to evaluate the methodology developed and data collected in the South African Environmental Observation Network’s, Elwandle Coastal Node as part of the Shallow Marine and Coastal Research Infrastructure Benthic Ecosystem Long-Term Ecological Research (BELTER) platform. Newly designed and developed sample equipment and a sampling regime allowed for the collection of data on a long-term basis. The study was successful in the description of the biotope and biotope subunits for two research stations in Algoa Bay. It permitted the construction of comprehensive species lists for both benthic sessile and sedentary biota and the associated ichthyofauna. The subset of data used was successful in reporting on both spatial and temporal change. This work demonstrates that in the absence of detailed species identifications, traits may be used to describe habitat and community structure and report on abiotic and biotic biotope characteristics. This study furthermore allowed for the comparison of a comprehensive suite of diversity indices highlighting indices that may be especially useful in routine BELTER reporting. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Parker-Nance, Shirley
- Date: 2021-10-29
- Subjects: Benthic ecology South Africa Algoa Bay , Long-Term Ecological Research Program , Marine invertebrates South Africa Algoa Bay , Reef ecology South Africa Algoa Bay , Coastal zone management South Africa Algoa Bay , Reef fishes South Africa Algoa Bay , Ecological mapping South Africa Algoa Bay
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191680 , vital:45147 , 10.21504/10962/191680
- Description: Shallow coastal marine ecosystems provide important resources to society but are increasingly under threat from anthropogenic impacts. These systems form an interface between land and sea, providing valuable resources. Global environmental change, overexploitation, habitat transformation, pollution and policies aimed at short-term socio-economic gains are driving the loss of natural resources, productivity and biodiversity. Consequently, a comprehensive and holistic understanding of the current and future states of marine ecosystems is essential. This requires insight into the processes involved in maintaining genetic, species, habitat, community and biotope diversity at an ecosystem level. An understanding of ecosystem processes and the ability to detect changes in biodiversity, biotopes, seascape composition and ecosystem functioning require observation made over time and space. In response to this need, Long-Term Ecological Research (LTER) programmes such as those established by the South African Environmental Observation Network (SAEON) supported by the Department of Science and Innovation’s (DSI) Shallow Marine and Coastal Research Infrastructure (SMCRI) collect long–term observational data from different environments and systems. This study aimed to evaluate data collected as part of the developmental phase of a newly established benthic research platform. The datasets constructed are used to develop a baseline description of the benthic biotopes of two study areas within Algoa Bay. It aimed to gain insight into the feasibility of the methods used and the value of the data and derived essential biological variables (EVB). Assessing the sustainability of the programme over time was done through a practical evaluation of the methodology to be used and the technical feasibility of data collection and analysis. It furthermore aimed to assess the data usefulness in describing biodiversity at various scales and its sensitivity in reporting change. This pilot study provides valuable insight into data collection methodologies and introduces new sampling platforms. The baseline dataset consisted of data collected during the first 18 months of the SAEON Benthic Ecosystem Long-Term Ecological Research (BELTER) platform in Algoa Bay, Agulhas ecoregion, Western Indian Ocean, South Africa. This comprised of the collection of images for 150 m2 of the researched benthic seascape and 306 stereo video data streams. The 77 760 point dataset allowed the identification of 12 substrate types, 7 biotopes, 44 sub-biotope units, 377 sessile and sedentary benthic species and 51 ichthyofauna species. The described habitat and benthic communities and the defined benthic biotopes allowed for the assessment of biotope heterogeneity and the construction of a provisional distribution map for the broader biotopes. This work includes a study into the infra- and supra-benthic ichthyofauna associated with the defined biotopes and investigates the role habitat and benthic communities play in the distribution of these fish 3 assemblages. Lastly, it assesses the value of morphological traits and diversity indices for describing and comparing abiotic and biotic components of observed systems within the shallow coastal marine seascape. This study shows that species composition differs significantly between biotopes with habitat type playing a key role in the composition of the benthos. Substrate type, consolidated or unconsolidated, depth and the composition of the soft sediment is the most important determining factors. The White Sands Reef station has a higher species diversity than the St Croix Island Complex station with a higher percentage cover associated with the hard substrate. The dissimilarity between biotopes and communities are generally high although similarity within the biotopes or communities was found to be relatively low. This was considered indicative of high heterogeneity within the biotopes and a patch or mosaic-like distribution of communities within the broader biotope. A fine-scale a posteriori analysis of the data collected confirmed the high heterogeneous nature of both habitat and communities within the broader biotope. The description of the abiotic and biotic variables resulted in the identification of a diverse suite of biotope subunits. The character of the biotope hinges not only on the composition of the substrate and biota present but the contribution of smaller distinct biotopes subunits, their distribution and representation within broader biotopes and the degree these are shared with other broader biotopes. The distribution of these biotope units at different scales is believed to be important in understanding inherent diversity, niche partitioning and connectivity within a highly heterogeneous seascape. Ichthyofauna associated with the broader biotopes were indicative of the substrate type. Low profile reef systems with interspaced sandy stretches supported both reef fish and those typically associated with sandy substrates. Benthic biotopes associated characteristically with higher profile reef systems and less sand or soft sediment were mainly utilized by reef-associated fish species. Substrate type, depth and seasonality were found to be important factors in the observed composition and distribution of ichthyofauna over the seascape. Although fish species were found to have a wide distribution and made use of multiple biotopes the average abundance of the species within the observed assemblages differed. Analysis of ichthyofauna species composition indicated that observed fish assemblages were homogeneous within five of the seven biotopes. Broader biotopes that were found to be significantly different between sample locations are characterised by a diverse complement of biotope subunits and are highly heterogeneous. Traits and diversity indices are important tools for assessing and comparing different systems within the seascape, both spatially and temporally. The classification of the biota into broader phylogenetic groups indicated a significant difference between biotopes. This is especially useful when detailed 4 analysis or species identification is not possible or the skill set is not available. Morphological traits included in this study informed on the physical structure of the communities present and in combination with substrate type provided insight into the three-dimensional structure of the biotope. Species diversity, abundance, density estimates and the Shannon-Weiner diversity index were found to be the most useful diversity indices characterising and comparing biotopes. This was less so for ichthyofauna. Significant differences in the number of species observed were evident only between consolidated and unconsolidated dominated substrates. Although there was no significant difference in the number of individuals observed, both the Shannon-Weiner and Simpson Diversity indices were able to highlight differences in the fish assemblages observed for the different biotopes. The data collected, although permitting a comprehensive baseline assessment of the benthic environment for two research stations within the SAEON Algoa Bay LTER Sentinel Site, is temporally limited. The ichthyofauna dataset used was small and it is understood that the addition of length-frequency analysis of observed ichthyofauna will benefit our understanding of the biotope use by infra- and supra-benthic fish species over their life history within the larger seascape. Seasonal differences were evident and it is expected that datasets spanning several years, including LTER stations within different marine ecosystems types, will provide valuable insights on system dynamics in the short and long term both spatially and temporally. This study is the first attempt to evaluate the methodology developed and data collected in the South African Environmental Observation Network’s, Elwandle Coastal Node as part of the Shallow Marine and Coastal Research Infrastructure Benthic Ecosystem Long-Term Ecological Research (BELTER) platform. Newly designed and developed sample equipment and a sampling regime allowed for the collection of data on a long-term basis. The study was successful in the description of the biotope and biotope subunits for two research stations in Algoa Bay. It permitted the construction of comprehensive species lists for both benthic sessile and sedentary biota and the associated ichthyofauna. The subset of data used was successful in reporting on both spatial and temporal change. This work demonstrates that in the absence of detailed species identifications, traits may be used to describe habitat and community structure and report on abiotic and biotic biotope characteristics. This study furthermore allowed for the comparison of a comprehensive suite of diversity indices highlighting indices that may be especially useful in routine BELTER reporting. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2021
- Full Text:
- Date Issued: 2021-10-29
Progress in implementing the ecosystem approach to fisheries in South Africa in principle and in practice
- Duna, Elethu Zamandlane Lona
- Authors: Duna, Elethu Zamandlane Lona
- Date: 2017
- Subjects: Fisheries -- Environmental aspects -- South Africa , Sustainable fisheries -- South Africa , Fishery management -- South Africa , South African Sustainable Seafood Initiative
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/44879 , vital:25449
- Description: Over the last century, the population of the world has more than doubled, resulting in an increase in seafood consumption (FAO 2010), and placing strain on fisheries wild stocks, their habitats, and the coastal communities that rely on them for food and survival. The ecosystem approach to fisheries (EAF) differs from other management approaches by combining all aspects of ecosystem management, and strives to conserve ecosystem structure, maintain diversity, productivity, and integrity, and to meet human food and economic needs. This study aims to assess how South Africa is progressing in implementing EAF in principle and in practice, to identify challenges, and suggest solutions, where appropriate. The law sets precedence on governance. An assessment of the Marine Living Resources Act, (MLRA) and the South African Policy for Small-scale Fisheries (SSFP) revealed that, although these instruments recognise and contain elements of EAF, this management approach has not been adequately implemented. In practice, the status of implementation of EAF was assessed through the Southern African Sustainable Seafood Initiative (SASSI) and the Ecological Risk Assessments (ERA). The scores of 65 assessments, conducted in 2013 and 2014, were obtained from SASSI. Of the 65 species assessed; 18.4% were listed as Green, 50.8% were listed as Orange and 30.8% were listed as Red. Two methods were used to analyse the data; non-metric multidimensional scaling (NMDS), and cluster analysis in the statistical program R. Analysis of the SASSI assessments indicates that there has been progress in implementing EAF since the World Summit on Sustainable Development in 2002. The high number of Orange and Red listed species however, indicate that major sustainability issues still exist. Species in commercially important fisheries enjoy the bulk of research and management attention compared to other species, including bycatch species, as reflected by a high proportion of Green-rated commercially important species. Based on these results, four fisheries were chosen for further indepth analysis using additional information found in ecological risk assessments: offshore demersal trawl, inshore demersal trawl, West Coast rock lobster fishery and the line fishery. The documents and published literature of the Department of Agriculture, Forestry and Fisheries Internal Scientific Working Groups provided further information. A Wilcoxon signed rank test conducted in the programme R on the results of the ERAs showed that there was a decline in implementation of EAF and reinforced the earlier conclusion that large commercial fisheries, offshore and inshore demersal trawl, were progressing in implementing EAF faster than West Coast rock lobster and line fisheries, which are examples of smaller-scale fisheries that are more accessible to many resource users. Both progress and challenges appeared to be largely influenced by several common factors, which include the presence or absence of positive incentives, co-management, management plans, access, compliance, economic importance, capacity, and the interests of rights holders and other stakeholders.
- Full Text:
- Date Issued: 2017
- Authors: Duna, Elethu Zamandlane Lona
- Date: 2017
- Subjects: Fisheries -- Environmental aspects -- South Africa , Sustainable fisheries -- South Africa , Fishery management -- South Africa , South African Sustainable Seafood Initiative
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/44879 , vital:25449
- Description: Over the last century, the population of the world has more than doubled, resulting in an increase in seafood consumption (FAO 2010), and placing strain on fisheries wild stocks, their habitats, and the coastal communities that rely on them for food and survival. The ecosystem approach to fisheries (EAF) differs from other management approaches by combining all aspects of ecosystem management, and strives to conserve ecosystem structure, maintain diversity, productivity, and integrity, and to meet human food and economic needs. This study aims to assess how South Africa is progressing in implementing EAF in principle and in practice, to identify challenges, and suggest solutions, where appropriate. The law sets precedence on governance. An assessment of the Marine Living Resources Act, (MLRA) and the South African Policy for Small-scale Fisheries (SSFP) revealed that, although these instruments recognise and contain elements of EAF, this management approach has not been adequately implemented. In practice, the status of implementation of EAF was assessed through the Southern African Sustainable Seafood Initiative (SASSI) and the Ecological Risk Assessments (ERA). The scores of 65 assessments, conducted in 2013 and 2014, were obtained from SASSI. Of the 65 species assessed; 18.4% were listed as Green, 50.8% were listed as Orange and 30.8% were listed as Red. Two methods were used to analyse the data; non-metric multidimensional scaling (NMDS), and cluster analysis in the statistical program R. Analysis of the SASSI assessments indicates that there has been progress in implementing EAF since the World Summit on Sustainable Development in 2002. The high number of Orange and Red listed species however, indicate that major sustainability issues still exist. Species in commercially important fisheries enjoy the bulk of research and management attention compared to other species, including bycatch species, as reflected by a high proportion of Green-rated commercially important species. Based on these results, four fisheries were chosen for further indepth analysis using additional information found in ecological risk assessments: offshore demersal trawl, inshore demersal trawl, West Coast rock lobster fishery and the line fishery. The documents and published literature of the Department of Agriculture, Forestry and Fisheries Internal Scientific Working Groups provided further information. A Wilcoxon signed rank test conducted in the programme R on the results of the ERAs showed that there was a decline in implementation of EAF and reinforced the earlier conclusion that large commercial fisheries, offshore and inshore demersal trawl, were progressing in implementing EAF faster than West Coast rock lobster and line fisheries, which are examples of smaller-scale fisheries that are more accessible to many resource users. Both progress and challenges appeared to be largely influenced by several common factors, which include the presence or absence of positive incentives, co-management, management plans, access, compliance, economic importance, capacity, and the interests of rights holders and other stakeholders.
- Full Text:
- Date Issued: 2017
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