A spatial perspective of the population structure and connectivity of two small tuna species, Katsuwonus pelamis (Skipjack tuna) and Euthynnus affinis (Kawakawa), in the Southwest Indian Ocean
- Authors: Taylor, Christopher John
- Date: 2024-10-11
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/467116 , vital:76816
- Description: Katsuwonus pelamis and Euthynnus affinis are two small tuna species of socio-economic and fisheries importance across the Southwest Indian Ocean (SWIO). There is currently a dearth of data and information around various aspects of their biology in the SWIO, including their population structure and connectivity. The availability of such data, including spatially represented biological data, has the potential to address current management discrepancies through the provision of more robust assessments into the stock structure and connectivity of these species and their stocks. This study explored a spatial perspective of the population structure and connectivity of K. pelamis and E. affinis fisheries in the SWIO to determine the suitability of current Indian Ocean Tuna Commission (IOTC) management measures for the species. It employed two primary data sources: a) Western Indian Ocean Marine Science Association’s (WIOMSA) Marine and Coastal Science for Management (MASMA) Project and b) IOTC. WIOMSA MASMA and IOTC data was collected throughout many countries and small island states in the SWIO, and pertained to genetic diversity, catch-weight, length-at-maturity, and morphometrics. Such data were combined and analysed to conduct geospatial analysis. Spatially illustrated genetic divergence, length-at-maturity, catch-weight, and morphometric data supported the presence of three reproductively isolated subpopulations of K. pelamis in the SWIO (Dar es Salaam, Tanzania, and Kenya; Mtwara, Tanzania, Mozambique, and Eastern Cape, South Africa; Seychelles). Only spatially depicted genetic divergence data, and morphometrics, supported that E. affinis populations were not panmictic in the SWIO, with genetic divergence data supporting the presence of three reproductively isolated subpopulations of E. affinis (Northern Mozambique and Kenya; Tanzania; Seychelles). Spatially illustrated length-at-maturity and catch-weight data however did not provide sufficient evidence supporting spatial structuring among E. affinis populations in the SWIO. Whilst the present analyses are not definitive to delineate exact stock boundaries, findings supported the contention of current IOTC management policy, indicating spatial population complexity for both species. Future research must increase representation of fishery independent samples and must investigate oceanographic variables driving potential stock separation to further support effective management reform. Until available, a precautionary approach should be adopted for the management of these species across the SWIO, considering the presently proposed distribution of their stocks separate for management. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Taylor, Christopher John
- Date: 2024-10-11
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/467116 , vital:76816
- Description: Katsuwonus pelamis and Euthynnus affinis are two small tuna species of socio-economic and fisheries importance across the Southwest Indian Ocean (SWIO). There is currently a dearth of data and information around various aspects of their biology in the SWIO, including their population structure and connectivity. The availability of such data, including spatially represented biological data, has the potential to address current management discrepancies through the provision of more robust assessments into the stock structure and connectivity of these species and their stocks. This study explored a spatial perspective of the population structure and connectivity of K. pelamis and E. affinis fisheries in the SWIO to determine the suitability of current Indian Ocean Tuna Commission (IOTC) management measures for the species. It employed two primary data sources: a) Western Indian Ocean Marine Science Association’s (WIOMSA) Marine and Coastal Science for Management (MASMA) Project and b) IOTC. WIOMSA MASMA and IOTC data was collected throughout many countries and small island states in the SWIO, and pertained to genetic diversity, catch-weight, length-at-maturity, and morphometrics. Such data were combined and analysed to conduct geospatial analysis. Spatially illustrated genetic divergence, length-at-maturity, catch-weight, and morphometric data supported the presence of three reproductively isolated subpopulations of K. pelamis in the SWIO (Dar es Salaam, Tanzania, and Kenya; Mtwara, Tanzania, Mozambique, and Eastern Cape, South Africa; Seychelles). Only spatially depicted genetic divergence data, and morphometrics, supported that E. affinis populations were not panmictic in the SWIO, with genetic divergence data supporting the presence of three reproductively isolated subpopulations of E. affinis (Northern Mozambique and Kenya; Tanzania; Seychelles). Spatially illustrated length-at-maturity and catch-weight data however did not provide sufficient evidence supporting spatial structuring among E. affinis populations in the SWIO. Whilst the present analyses are not definitive to delineate exact stock boundaries, findings supported the contention of current IOTC management policy, indicating spatial population complexity for both species. Future research must increase representation of fishery independent samples and must investigate oceanographic variables driving potential stock separation to further support effective management reform. Until available, a precautionary approach should be adopted for the management of these species across the SWIO, considering the presently proposed distribution of their stocks separate for management. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
Assessing the vulnerability of inland fisheries to human-induced perturbation in Lake Kariba fishery, Zambia
- Authors: Imikendu, Imbwae
- Date: 2024-10-11
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466725 , vital:76774 , DOI https://doi.org/10.21504/10962/466725
- Description: Inland fisheries play a critical role in providing nutrition, employment, and ensuring food security among vulnerable groups in Lake Kariba. However, their value is usually undermined in developmental plans, and their contribution to a broader economic development is often undervalued. Over the past two decades, inland fisheries have stagnated. Simultaneously, there have been wide reports of increased fishing effort and declining trends in commercially valuable fish species. This has resulted into a wide socio-economic and environmental problems in various fishing communities. Lake Kariba Zambia, exemplifies this sustainability challenge, where fisheries resources and livelihoods are interlinked. A systematic peer review paper on this topic was documented, published and used for analytical work, focusing on governance and how it affects the utilization of the fisheries resources for food security and biodiversity conservation. This study had four major objectives: (i) to identify threats to fisheries’ productivity in Lake Kariba; (ii) to understand the socio-economic and environmental conditions of small-scale fisheries in Lake Kariba; (iii) to determine adaptation strategies adopted by small-scale fishers in light of the changing socio-economic and environmental conditions in Lake Kariba; (iv) to determine how management of fisheries has to change in response to the wide socio-economic and environmental challenges in the region. Using Ostrom’s framework for analysing socio-ecological systems, various socioeconomic and environmental problems faced by fishing communities in Lake Kariba were examined to devise a sustainable fisheries management plan. The study employed explorative surveys, household questionnaires, key informant interviews, focus group discussions, observations, and a review of literature to elicit secondary data. A proportional quota sampling technique was used to draw a representative sample of 300 small-scale fishers and a typology was developed using a bivariate analysis. Chi-square was used to determine fishing effort over time. Using a curve fitting estimation regression test, a trend analysis in fish production for the past thirteen years (13) years was performed. Results did not show a significant decline in fish production over the past 13 years, yet experts and the fishers reported declining trends in valuable fish species. The finding of this study provides both practical and theoretical lessons that can enhance adaptive capacity and support sustainable livelihoods in the region. A fisheries sector policy is urgently required to guide governance process and coordinate a multi-sectoral perspective to fisheries management if socio-economic progression is to be attained. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Imikendu, Imbwae
- Date: 2024-10-11
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466725 , vital:76774 , DOI https://doi.org/10.21504/10962/466725
- Description: Inland fisheries play a critical role in providing nutrition, employment, and ensuring food security among vulnerable groups in Lake Kariba. However, their value is usually undermined in developmental plans, and their contribution to a broader economic development is often undervalued. Over the past two decades, inland fisheries have stagnated. Simultaneously, there have been wide reports of increased fishing effort and declining trends in commercially valuable fish species. This has resulted into a wide socio-economic and environmental problems in various fishing communities. Lake Kariba Zambia, exemplifies this sustainability challenge, where fisheries resources and livelihoods are interlinked. A systematic peer review paper on this topic was documented, published and used for analytical work, focusing on governance and how it affects the utilization of the fisheries resources for food security and biodiversity conservation. This study had four major objectives: (i) to identify threats to fisheries’ productivity in Lake Kariba; (ii) to understand the socio-economic and environmental conditions of small-scale fisheries in Lake Kariba; (iii) to determine adaptation strategies adopted by small-scale fishers in light of the changing socio-economic and environmental conditions in Lake Kariba; (iv) to determine how management of fisheries has to change in response to the wide socio-economic and environmental challenges in the region. Using Ostrom’s framework for analysing socio-ecological systems, various socioeconomic and environmental problems faced by fishing communities in Lake Kariba were examined to devise a sustainable fisheries management plan. The study employed explorative surveys, household questionnaires, key informant interviews, focus group discussions, observations, and a review of literature to elicit secondary data. A proportional quota sampling technique was used to draw a representative sample of 300 small-scale fishers and a typology was developed using a bivariate analysis. Chi-square was used to determine fishing effort over time. Using a curve fitting estimation regression test, a trend analysis in fish production for the past thirteen years (13) years was performed. Results did not show a significant decline in fish production over the past 13 years, yet experts and the fishers reported declining trends in valuable fish species. The finding of this study provides both practical and theoretical lessons that can enhance adaptive capacity and support sustainable livelihoods in the region. A fisheries sector policy is urgently required to guide governance process and coordinate a multi-sectoral perspective to fisheries management if socio-economic progression is to be attained. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
Fishery characteristics, genetic structure, population demography and value chain of Skipjack and Kawakawa exploited in coastal waters of the Western Indian Ocean
- Authors: Mzingirwa, Fatuma Ali
- Date: 2024-10-11
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466759 , vital:76776 , DOI https://doi.org/10.21504/10962/466759
- Description: Tuna represents a highly valuable global fishery, comprising 7.9% of the total 67.9 million metric tons (MT) of marine finfish catch. Among tuna species, Katsuwonus pelamis, skipjack and Euthynnus affinis, kawakawa are commercially important, particularly for artisanal fisheries. Skipjack is the most dominant tuna species globally, contributing over 60% to total tuna production. In the Indian Ocean (IO), skipjack catches approximately 420,000 MT annually. Kawakawa, the second most abundant neritic tuna in the IO, accounting for roughly 12% of neritic tuna landings, is primarily harvested by artisanal fleets, with annual catches of around 160,000 MT. While current assessments indicate that skipjack and kawakawa stocks in the IO are not overfished, maintaining their long-term health is crucial. This research addresses three key areas: genetic diversity, population structure, and connectivity of skipjack and kawakawa tuna in the Western Indian Ocean (WIO); size structure and reproductive characteristics of these species within the WIO; and the value chain of the Kenyan artisanal tuna fishery, focusing on skipjack and kawakawa. To achieve these objectives, skipjack and kawakawa samples were collected from Kenya, Tanzania, Mozambique, and South Africa. A non-random sampling approach was employed to obtain specimens and data from artisanal and recreational fisheries. Biological and genetic sampling were conducted concurrently. The economic value chain of the Kenyan artisanal tuna fishery was examined through questionnaires and catch data. This analysis focused on the socio-demographic profiles of key actors, the value chain structure, and associated economic benefits across four Kenyan landing sites. To investigate stock structure in WIO skipjack and kawakawa tuna, we employed tunable Genotyping-by-Sequencing (tGBS) to generate genome-wide Single Nucleotide Polymorphism (SNP) data. Skipjack analysis revealed 7005 SNPs with an average observed heterozygosity (Ho) of 0.206. While overall genetic differentiation (FST) among samples was low (global FST = 0.003) between samples (FST = 0 – 0.013), significant genetic differences were observed between skipjack samples taken north of Mtwara in southern Tanzania (i.e., northern Tanzania, Kenya and Sri Lanka) and those to the south (i.e., southern Tanzania, Mozambique and South Africa), with Seychelles falling closer to the southern grouping. Kawakawa analysis, based on 14806 SNPs and an average Ho of 0.2585, indicated a patchy distribution of low but significant genetic differentiation among WIO populations (global FST = 0.018) between-sample (FST = 0.003 – 0.036) but with no obvious geographically-based pattern. However, unlike skipjack, a clear geographic pattern in genetic structure was not evident for kawakawa. Skipjack and kawakawa populations in the WIO exhibited seasonal fluctuations in size distribution, potentially influenced by environmental conditions and fishing practices. Landings of both species were male-biased, with sex ratios of 58% and 53% for skipjack and kawakawa, respectively. Female skipjack reached sexual maturity at a fork length (FL) of 42.0 cm, while males matured at 47.0 cm FL. For kawakawa, female and male maturation lengths were 44.0 cm FL and 45.3 cm FL, respectively. Spawning occurred throughout the year, with peak activity coinciding with the Northeast Monsoon (NEM) season. Our analysis of the artisanal tuna value chain indicates that fishers primarily sell their catch to agents (53%), with the remaining proportions going to traders (20%) and processors (18%). Processors, predominantly women, play a key role in the value chain and realized the highest net profit margin (49.5%). Limited post-harvest infrastructure, inadequate transportation, and poor marketing conditions were identified as key challenges impacting the quality of fish lowering their income. These challenges disproportionately affect fishers with limited access to market information and financial resources. The findings demonstrate the need for multi-level interventions to optimize benefits from the artisanal tuna fishery along the entire value chain taking into consideration the economic, environmental, and social dimensions. This research provides crucial information for effective tuna management in the IO. Current management practices treat skipjack and kawakawa as a single, homogenous population across the entire IO. However, our genetic findings suggest the presence of distinct population groups (stocks) for both species within the WIO. Moreover, seasonal variations in size structure and reproductive characteristics observed support this hypothesis of multiple stocks. These results emphasize the need for a precautionary approach to tuna management in the region. Collaborative efforts among countries are essential to develop sustainable fisheries management strategies that consider biological, economic, and social factors. By integrating these perspectives, we can ensure the long-term health of tuna populations while supporting the livelihoods of fishing communities. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Mzingirwa, Fatuma Ali
- Date: 2024-10-11
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466759 , vital:76776 , DOI https://doi.org/10.21504/10962/466759
- Description: Tuna represents a highly valuable global fishery, comprising 7.9% of the total 67.9 million metric tons (MT) of marine finfish catch. Among tuna species, Katsuwonus pelamis, skipjack and Euthynnus affinis, kawakawa are commercially important, particularly for artisanal fisheries. Skipjack is the most dominant tuna species globally, contributing over 60% to total tuna production. In the Indian Ocean (IO), skipjack catches approximately 420,000 MT annually. Kawakawa, the second most abundant neritic tuna in the IO, accounting for roughly 12% of neritic tuna landings, is primarily harvested by artisanal fleets, with annual catches of around 160,000 MT. While current assessments indicate that skipjack and kawakawa stocks in the IO are not overfished, maintaining their long-term health is crucial. This research addresses three key areas: genetic diversity, population structure, and connectivity of skipjack and kawakawa tuna in the Western Indian Ocean (WIO); size structure and reproductive characteristics of these species within the WIO; and the value chain of the Kenyan artisanal tuna fishery, focusing on skipjack and kawakawa. To achieve these objectives, skipjack and kawakawa samples were collected from Kenya, Tanzania, Mozambique, and South Africa. A non-random sampling approach was employed to obtain specimens and data from artisanal and recreational fisheries. Biological and genetic sampling were conducted concurrently. The economic value chain of the Kenyan artisanal tuna fishery was examined through questionnaires and catch data. This analysis focused on the socio-demographic profiles of key actors, the value chain structure, and associated economic benefits across four Kenyan landing sites. To investigate stock structure in WIO skipjack and kawakawa tuna, we employed tunable Genotyping-by-Sequencing (tGBS) to generate genome-wide Single Nucleotide Polymorphism (SNP) data. Skipjack analysis revealed 7005 SNPs with an average observed heterozygosity (Ho) of 0.206. While overall genetic differentiation (FST) among samples was low (global FST = 0.003) between samples (FST = 0 – 0.013), significant genetic differences were observed between skipjack samples taken north of Mtwara in southern Tanzania (i.e., northern Tanzania, Kenya and Sri Lanka) and those to the south (i.e., southern Tanzania, Mozambique and South Africa), with Seychelles falling closer to the southern grouping. Kawakawa analysis, based on 14806 SNPs and an average Ho of 0.2585, indicated a patchy distribution of low but significant genetic differentiation among WIO populations (global FST = 0.018) between-sample (FST = 0.003 – 0.036) but with no obvious geographically-based pattern. However, unlike skipjack, a clear geographic pattern in genetic structure was not evident for kawakawa. Skipjack and kawakawa populations in the WIO exhibited seasonal fluctuations in size distribution, potentially influenced by environmental conditions and fishing practices. Landings of both species were male-biased, with sex ratios of 58% and 53% for skipjack and kawakawa, respectively. Female skipjack reached sexual maturity at a fork length (FL) of 42.0 cm, while males matured at 47.0 cm FL. For kawakawa, female and male maturation lengths were 44.0 cm FL and 45.3 cm FL, respectively. Spawning occurred throughout the year, with peak activity coinciding with the Northeast Monsoon (NEM) season. Our analysis of the artisanal tuna value chain indicates that fishers primarily sell their catch to agents (53%), with the remaining proportions going to traders (20%) and processors (18%). Processors, predominantly women, play a key role in the value chain and realized the highest net profit margin (49.5%). Limited post-harvest infrastructure, inadequate transportation, and poor marketing conditions were identified as key challenges impacting the quality of fish lowering their income. These challenges disproportionately affect fishers with limited access to market information and financial resources. The findings demonstrate the need for multi-level interventions to optimize benefits from the artisanal tuna fishery along the entire value chain taking into consideration the economic, environmental, and social dimensions. This research provides crucial information for effective tuna management in the IO. Current management practices treat skipjack and kawakawa as a single, homogenous population across the entire IO. However, our genetic findings suggest the presence of distinct population groups (stocks) for both species within the WIO. Moreover, seasonal variations in size structure and reproductive characteristics observed support this hypothesis of multiple stocks. These results emphasize the need for a precautionary approach to tuna management in the region. Collaborative efforts among countries are essential to develop sustainable fisheries management strategies that consider biological, economic, and social factors. By integrating these perspectives, we can ensure the long-term health of tuna populations while supporting the livelihoods of fishing communities. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
Economically important cephalopods of southern Angola, with a focus on the artisanal jig fishery
- Vázquez Morán, Chénelle Lesley
- Authors: Vázquez Morán, Chénelle Lesley
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422529 , vital:71955 , DOI 10.21504/10962/422529
- Description: The global decline in marine finfish stocks has been met with a concomitant expansion of fisheries for cephalopods. Despite the increase in the exploitation and commercialization of cephalopods, there is a dearth of scientific information for over 90% of the extant species and this is even more marked in the developing world. Angolan capture fisheries production noted a tenfold increase in cephalopod landings between 1994 and 2003. One of the important fisheries is a cephalopod directed jig fishery that targets the squid Loligo reynaudii and the cuttlefish Sepia vermiculata in southern Angola, however, there is a complete lack of socio-ecological information available for this fishery. Hence the aim of this thesis was to provide basic biological and demographic information on L. reynaudii and S. vermiculata distributed off the coast of southern Angola, assess the importance and dependence of local artisanal fishers on these two species and examine the current management strategies and policies in the region This study found that the artisanal cephalopod jig fishery is critical for the livelihoods of the coastal communities of southern Angola, particularly due to the limited alternative income generating opportunities available. The cephalopod jig fishery is highly labour intensive, with fishers spending a considerable amount of time per day, drifting over known fishing grounds. Catch composition of the artisanal jig fishery indicated that squid is the dominant species within the fishery, in terms of numerical abundance and weight. The productivity and progression of the fishery is hampered by a number of ecological, socio-economic and governance constraints, as highlighted by socio-economic surveys conducted with local squid fishers. Such constraints include, but are not limited to declining catches, increased negative interactions with seals, increased inter-sector competition, lack of infrastructure, poor quality fishing equipment as well as a lack of communication and support from government officials. To examine aspects of the biology and demography of L. reynaudii, whole specimens were collected monthly, from the two primary fishing areas in southern Angola; Namibe and Tombua, during two main sampling periods, June 2008 – May 2009 (Period 1) and June 2014 – May 2015 (Period 2). Male L. reynaudii were found to be significantly larger in size and weight than females, however both the average and maximum dorsal mantle length (DML) decreased between sampling periods. Length-at-50% maturity was larger for male L. reynaudii (170.47 mm DML – 1st period, 165.44 mm DML – 2nd period) than female L. reynaudii (114.71 mm DML – 1st period, 109.43 mm DML – 2nd period). Gonadosomatic indices (GSI) varied significantly during month and season for both sexes. Peak GSI coincided with a low catches in the artisanal jig fishery suggesting that the population may undergo a spawning migration away from fishing grounds, during late spring and summer. The theory of a seasonal spawning migration is further supported in this study by the low abundance of juvenile and sub-adult L, reynaudii collected during the study, along with the inability to detect egg beds in known fishing grounds. Stomach content analysis indicated that teleosts were the most important dietary item (66.3% F of the stomach contents). Trachurus capensis and Engraulis encrasicolus are both highly abundant small pelagic fishes in the cold nutrient rich waters of the Benguela Current and dominated the diet of sampled squid during autumn and winter months. It is likely that the prevalence of large, adult squid off the coast of Angola, as observed within the current study, may be ascribed to the suitable environmental conditions and the abundance of suitable prey. The results from the current study indicate that the southern Angolan subpopulation reveals similarities to that of the West Coast subpopulation of squid in South Africa, with regards to demographics and reproductive characteristics. It is likely that the population in southern Angola is an extension of the South African subpopulation of L. reynaudii on the western extremities. To examine the basic population biology and ecology of S. vermiculata off southern Angola whole specimens were collected from the fishery between December 2014 and April 2015. Morphological results indicate clear sexual dimorphism in soft part characteristics, cuttlebone and beak morphometry. Length-at-50% maturity was smaller in male S. vermiculata (217.53 mm DML) than female S. vermiculata (231.13 mm DML), although these differences were not significant. Stomach content analysis indicated that S. vermiculata predominantly fed on teleost species which were found within 64.5% of stomachs. Teleosts were more dominant in the diet of male S. vermiculata (78.6% F) than female S. vermiculata (53.0% F), which ate a more varied diet including crustaceans (41.2% F) and cephalopods (17.7% F). Availability and abundance of cuttlefish in Namibe indicates that the species may undergo a spatio-temporal shift in distribution, with majority of the artisanal catches of S. vermiculata occurring during summer months. The results from the current study highlights the fisheries potential of L. reynaudii and S. vermiculata and the dependence of artisanal fishers in southern Angola on cephalopods, and more specifically squid. The development of sustainable fisheries management strategies for the artisanal cephalopod jig fishery is critical, particularly as the global exploitation of cephalopods continues to increase with declining finfish populations. Failure to implement management strategies may remove this critical economic safety net for vulnerable coastal communities which have little alternative livelihood opportunities. Ongoing ecological research, a co-management approach and an increased consideration of local ecological knowledge will assist in designing appropriate management plans for the southern Angolan cephalopod jig fishery. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-31
- Authors: Vázquez Morán, Chénelle Lesley
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422529 , vital:71955 , DOI 10.21504/10962/422529
- Description: The global decline in marine finfish stocks has been met with a concomitant expansion of fisheries for cephalopods. Despite the increase in the exploitation and commercialization of cephalopods, there is a dearth of scientific information for over 90% of the extant species and this is even more marked in the developing world. Angolan capture fisheries production noted a tenfold increase in cephalopod landings between 1994 and 2003. One of the important fisheries is a cephalopod directed jig fishery that targets the squid Loligo reynaudii and the cuttlefish Sepia vermiculata in southern Angola, however, there is a complete lack of socio-ecological information available for this fishery. Hence the aim of this thesis was to provide basic biological and demographic information on L. reynaudii and S. vermiculata distributed off the coast of southern Angola, assess the importance and dependence of local artisanal fishers on these two species and examine the current management strategies and policies in the region This study found that the artisanal cephalopod jig fishery is critical for the livelihoods of the coastal communities of southern Angola, particularly due to the limited alternative income generating opportunities available. The cephalopod jig fishery is highly labour intensive, with fishers spending a considerable amount of time per day, drifting over known fishing grounds. Catch composition of the artisanal jig fishery indicated that squid is the dominant species within the fishery, in terms of numerical abundance and weight. The productivity and progression of the fishery is hampered by a number of ecological, socio-economic and governance constraints, as highlighted by socio-economic surveys conducted with local squid fishers. Such constraints include, but are not limited to declining catches, increased negative interactions with seals, increased inter-sector competition, lack of infrastructure, poor quality fishing equipment as well as a lack of communication and support from government officials. To examine aspects of the biology and demography of L. reynaudii, whole specimens were collected monthly, from the two primary fishing areas in southern Angola; Namibe and Tombua, during two main sampling periods, June 2008 – May 2009 (Period 1) and June 2014 – May 2015 (Period 2). Male L. reynaudii were found to be significantly larger in size and weight than females, however both the average and maximum dorsal mantle length (DML) decreased between sampling periods. Length-at-50% maturity was larger for male L. reynaudii (170.47 mm DML – 1st period, 165.44 mm DML – 2nd period) than female L. reynaudii (114.71 mm DML – 1st period, 109.43 mm DML – 2nd period). Gonadosomatic indices (GSI) varied significantly during month and season for both sexes. Peak GSI coincided with a low catches in the artisanal jig fishery suggesting that the population may undergo a spawning migration away from fishing grounds, during late spring and summer. The theory of a seasonal spawning migration is further supported in this study by the low abundance of juvenile and sub-adult L, reynaudii collected during the study, along with the inability to detect egg beds in known fishing grounds. Stomach content analysis indicated that teleosts were the most important dietary item (66.3% F of the stomach contents). Trachurus capensis and Engraulis encrasicolus are both highly abundant small pelagic fishes in the cold nutrient rich waters of the Benguela Current and dominated the diet of sampled squid during autumn and winter months. It is likely that the prevalence of large, adult squid off the coast of Angola, as observed within the current study, may be ascribed to the suitable environmental conditions and the abundance of suitable prey. The results from the current study indicate that the southern Angolan subpopulation reveals similarities to that of the West Coast subpopulation of squid in South Africa, with regards to demographics and reproductive characteristics. It is likely that the population in southern Angola is an extension of the South African subpopulation of L. reynaudii on the western extremities. To examine the basic population biology and ecology of S. vermiculata off southern Angola whole specimens were collected from the fishery between December 2014 and April 2015. Morphological results indicate clear sexual dimorphism in soft part characteristics, cuttlebone and beak morphometry. Length-at-50% maturity was smaller in male S. vermiculata (217.53 mm DML) than female S. vermiculata (231.13 mm DML), although these differences were not significant. Stomach content analysis indicated that S. vermiculata predominantly fed on teleost species which were found within 64.5% of stomachs. Teleosts were more dominant in the diet of male S. vermiculata (78.6% F) than female S. vermiculata (53.0% F), which ate a more varied diet including crustaceans (41.2% F) and cephalopods (17.7% F). Availability and abundance of cuttlefish in Namibe indicates that the species may undergo a spatio-temporal shift in distribution, with majority of the artisanal catches of S. vermiculata occurring during summer months. The results from the current study highlights the fisheries potential of L. reynaudii and S. vermiculata and the dependence of artisanal fishers in southern Angola on cephalopods, and more specifically squid. The development of sustainable fisheries management strategies for the artisanal cephalopod jig fishery is critical, particularly as the global exploitation of cephalopods continues to increase with declining finfish populations. Failure to implement management strategies may remove this critical economic safety net for vulnerable coastal communities which have little alternative livelihood opportunities. Ongoing ecological research, a co-management approach and an increased consideration of local ecological knowledge will assist in designing appropriate management plans for the southern Angolan cephalopod jig fishery. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-31
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