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Shark nets in KwaZulu-Natal : an evaluation of catches and alternatives
Bibliography: p. 147-160.
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2014
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| _version_ | 1867613148741107712 |
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| access_status_str | Open Access |
| author | Dudley, Sheldon Francis John |
| author2 | Griffiths, Charles L |
| author_browse | Dudley, Sheldon Francis John Griffiths, Charles L |
| author_facet | Griffiths, Charles L Dudley, Sheldon Francis John |
| author_sort | Dudley, Sheldon Francis John |
| collection | Thesis |
| description | Bibliography: p. 147-160. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/9269 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:31:31.816Z |
| 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:11427/9269 Shark nets in KwaZulu-Natal : an evaluation of catches and alternatives Dudley, Sheldon Francis John Griffiths, Charles L Zoology Bibliography: p. 147-160. Protective gillnets (shark nets) have been successful in reducing the frequency of shark attacks on the coast of KwaZulu-Natal (KZN), South Africa. This is achieved primarily through a reduction in numbers of large sharks. The nets also take a by-catch of dolphins, sea turtles, batoids and teleosts.Catch rates of most shark species declined initially but have shown no trend since the mid-1970s. Turtle and teleost stocks do not appear to be threatened by net mortalities, but there is concern about the sustainability of catches of the humpback dolphin. Certain batoids may have declined despite a high release rate. A published contention that shark netting has resulted in a proliferation of small sharks through reduced predation is re-examined and considered to be exaggerated. Reduced predation on dolphins, as a result of shark netting, is estimated. Considerably less fishing effort is applied in the shark control programs of New South Wales and Queensland, Australia, than in that of KZN. On the basis of a comparison of factors such as the nearshore physical environments and trends in shark catch and catch rate, it is concluded that the number of nets used in KZN could be reduced. To test whether a 70 cm mesh would continue to capture potentially dangerous sharks, while at the same time reducing by-catch, a gamma distribution model was used to determine length-specific selectivities in 50.8 cm and 70 cm mesh nets respectively. A reduction in relative selectivity from 81 to 25 for a shark of 1.6 m PCL would result from an increase in mesh size from 50.8 to 70 cm. Despite a probable reduction in catch of dolphins .and certain other by-catch species, the introduction of the larger mesh would constitute an unacceptable reduction in levels of bather safety. Baited lines, or drumlines, were tested as possible alternatives to gillnets. They demonstrated greater species selectivity for sharks, including a higher catch of two of the target species, Carcharhinus leucas and Galeocerdo cuvier, and also a reduced by-catch of nonshark animals. The probability of the bait being scavenged, or a shark being caught, was modelled in relation to a number of physical factors. Although there were insufficient data for a quantitative comparison of catch rates between nets and drumlines, the results indicated that an optimal solution may be to deploy a combination of nets, using the existing 50.8 cm mesh, and drumlines, using 14/0 shark hooks. 2014-11-05T17:41:12Z 2014-11-05T17:41:12Z 1996 Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/9269 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Zoology Dudley, Sheldon Francis John Shark nets in KwaZulu-Natal : an evaluation of catches and alternatives |
| thesis_degree_str | Doctoral |
| title | Shark nets in KwaZulu-Natal : an evaluation of catches and alternatives |
| title_full | Shark nets in KwaZulu-Natal : an evaluation of catches and alternatives |
| title_fullStr | Shark nets in KwaZulu-Natal : an evaluation of catches and alternatives |
| title_full_unstemmed | Shark nets in KwaZulu-Natal : an evaluation of catches and alternatives |
| title_short | Shark nets in KwaZulu-Natal : an evaluation of catches and alternatives |
| title_sort | shark nets in kwazulu natal an evaluation of catches and alternatives |
| topic | Zoology |
| url | http://hdl.handle.net/11427/9269 |
| work_keys_str_mv | AT dudleysheldonfrancisjohn sharknetsinkwazulunatalanevaluationofcatchesandalternatives |