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Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches
Includes bibliographical references (p. 207-227)
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2014
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| _version_ | 1867613338803896320 |
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| access_status_str | Open Access |
| author | Ghebrehiwet, Dawit Yemane |
| author2 | Field, John G |
| author_browse | Field, John G Ghebrehiwet, Dawit Yemane |
| author_facet | Field, John G Ghebrehiwet, Dawit Yemane |
| author_sort | Ghebrehiwet, Dawit Yemane |
| collection | Thesis |
| description | Includes bibliographical references (p. 207-227) |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/8919 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:34:33.896Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2014 |
| publishDateRange | 2014 |
| publishDateSort | 2014 |
| publisher | Department of Biological Sciences |
| publisherStr | Department of Biological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/8919 Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches Ghebrehiwet, Dawit Yemane Field, John G Leslie, Rob W Shin, Yunne-jai Zoology Includes bibliographical references (p. 207-227) 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. 2014-10-29T10:08:32Z 2014-10-29T10:08:32Z 2007 Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/8919 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Zoology Ghebrehiwet, Dawit Yemane Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches |
| thesis_degree_str | Doctoral |
| title | Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches |
| title_full | Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches |
| title_fullStr | Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches |
| title_full_unstemmed | Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches |
| title_short | Assessing the effects of fishing on fish communities using South African case studies : empirical and theoretical approaches |
| title_sort | assessing the effects of fishing on fish communities using south african case studies empirical and theoretical approaches |
| topic | Zoology |
| url | http://hdl.handle.net/11427/8919 |
| work_keys_str_mv | AT ghebrehiwetdawityemane assessingtheeffectsoffishingonfishcommunitiesusingsouthafricancasestudiesempiricalandtheoreticalapproaches |