Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches
| dc.contributor.advisor | Field, John G | en_ZA |
| dc.contributor.advisor | Leslie, Rob W | en_ZA |
| dc.contributor.advisor | Shin, Yunne-jai | en_ZA |
| dc.contributor.author | Ghebrehiwet, Dawit Yemane | en_ZA |
| dc.date.accessioned | 2014-10-29T10:08:32Z | |
| dc.date.available | 2014-10-29T10:08:32Z | |
| dc.date.issued | 2007 | en_ZA |
| dc.description | Includes bibliographical references (p. 207-227) | en_ZA |
| dc.description.abstract | Currently heavy fishing is recognized as one of the major threats to the structural and functional organization of marine ecosystems in many coastal nations. The threat is mainly the result of the inherent nature of the various fishing activities: size selectivity, habitat destruction, biomass removal, and uncertainty in resource status and management of the resource. Thus this thesis investigates structural changes that result from fishing. This thesis aims to answer whether there were changes in the structure of fish communities off the of South Africa using two case studies, to explore the response of fish communities to the proposed creation of Marine Protected Areas and to investigate the alternate application of spatially uniform and heterogeneous fishing mortalities. The research questions of the thesis are answered through empirical analysis of landing data for the line fishery and analysis of demersal trawl survey data from the south coast of South Africa, and analysis of output of the Individual Based Model OSMOSE applied to the southern Benguela. Structural changes in the landings from the line fishery and south coast survey data are assessed using a variety of ecosystem indicators believed to capture such changes: size-based indicators {mean size, slope and height of the size spectra, mean Lmax7, proportion of size classes), species-based indicators (ordination by multidimensional scaling, and dendrograms, various diversity indices, dominance curves). Inferences are based on the reference directions of the indicators, according to the expected response of indicators to heavy fishing. Structural changes in the fish communities are observed, over the spatial and temporal bounds of the two case studies, to be the most likely cause of the observed changes is heavy fishing, although the influence of environmental factors cannot he ruled out. investigation of alternative implementation fishing mortality using the simulation model OSMOSE showed that the system and species biomass do differ between the two implementations, but the variability in the system remains the same. The modelled response of fish communities to the introduction of Marine Protected Areas is an overall increase in relative biomass of large predatory fishes and a decline in the biomass of prey and competitor species. | en_ZA |
| dc.identifier.apacitation | Ghebrehiwet, D. Y. (2007). <i>Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/8919 | en_ZA |
| dc.identifier.chicagocitation | Ghebrehiwet, Dawit Yemane. <i>"Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2007. http://hdl.handle.net/11427/8919 | en_ZA |
| dc.identifier.citation | Ghebrehiwet, D. 2007. Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches. University of Cape Town. | en_ZA |
| dc.identifier.ris | TY - Thesis / Dissertation AU - Ghebrehiwet, Dawit Yemane AB - Currently heavy fishing is recognized as one of the major threats to the structural and functional organization of marine ecosystems in many coastal nations. The threat is mainly the result of the inherent nature of the various fishing activities: size selectivity, habitat destruction, biomass removal, and uncertainty in resource status and management of the resource. Thus this thesis investigates structural changes that result from fishing. This thesis aims to answer whether there were changes in the structure of fish communities off the of South Africa using two case studies, to explore the response of fish communities to the proposed creation of Marine Protected Areas and to investigate the alternate application of spatially uniform and heterogeneous fishing mortalities. The research questions of the thesis are answered through empirical analysis of landing data for the line fishery and analysis of demersal trawl survey data from the south coast of South Africa, and analysis of output of the Individual Based Model OSMOSE applied to the southern Benguela. Structural changes in the landings from the line fishery and south coast survey data are assessed using a variety of ecosystem indicators believed to capture such changes: size-based indicators {mean size, slope and height of the size spectra, mean Lmax7, proportion of size classes), species-based indicators (ordination by multidimensional scaling, and dendrograms, various diversity indices, dominance curves). Inferences are based on the reference directions of the indicators, according to the expected response of indicators to heavy fishing. Structural changes in the fish communities are observed, over the spatial and temporal bounds of the two case studies, to be the most likely cause of the observed changes is heavy fishing, although the influence of environmental factors cannot he ruled out. investigation of alternative implementation fishing mortality using the simulation model OSMOSE showed that the system and species biomass do differ between the two implementations, but the variability in the system remains the same. The modelled response of fish communities to the introduction of Marine Protected Areas is an overall increase in relative biomass of large predatory fishes and a decline in the biomass of prey and competitor species. DA - 2007 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2007 T1 - Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches TI - Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches UR - http://hdl.handle.net/11427/8919 ER - | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11427/8919 | |
| dc.identifier.vancouvercitation | Ghebrehiwet DY. Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2007 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/8919 | en_ZA |
| dc.language.iso | eng | en_ZA |
| dc.publisher.department | Department of Biological Sciences | en_ZA |
| dc.publisher.faculty | Faculty of Science | en_ZA |
| dc.publisher.institution | University of Cape Town | |
| dc.subject.other | Zoology | en_ZA |
| dc.title | Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches | en_ZA |
| dc.type | Doctoral Thesis | |
| dc.type.qualificationlevel | Doctoral | |
| dc.type.qualificationname | PhD | en_ZA |
| uct.type.filetype | Text | |
| uct.type.filetype | Image | |
| uct.type.publication | Research | en_ZA |
| uct.type.resource | Thesis | en_ZA |
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