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Bycatch in the South African midwater trawl fishery for horse mackerel (Trachurus capensis) as established from observer records
The South African midwater trawl fishery targets adult horse mackerel (Trachurus capensis) on the Agulhas Bank. The bulk of the catch is taken by a single midwater trawler. The bycatch of this fishery is investigated by analysing observer records from 2004 to 2014 to report on bycatch composition, v...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2016
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| _version_ | 1867613163684364288 |
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| access_status_str | Open Access |
| author | Reed, Jodie Romay |
| author2 | Attwood, Colin |
| author_browse | Attwood, Colin Reed, Jodie Romay |
| author_facet | Attwood, Colin Reed, Jodie Romay |
| author_sort | Reed, Jodie Romay |
| collection | Thesis |
| description | The South African midwater trawl fishery targets adult horse mackerel (Trachurus capensis) on the Agulhas Bank. The bulk of the catch is taken by a single midwater trawler. The bycatch of this fishery is investigated by analysing observer records from 2004 to 2014 to report on bycatch composition, volumes and temporal and spatial patterns. Small fauna were analysed by extrapolation of sample weights and large fauna were counted. The midwater trawl fishery was estimated to have caught 25 415 t annually, with a bycatch rate of 6.9% of the total catch, by weight. Bycatch species with the highest average annual catches were chub mackerel (Scomber japonicus), redeye roundherring (Etrumeus whiteheadi), ribbonfish (Lepidopus caudatus) and hake (Merluccius spp.). Large fauna bycatch species included Cape fur seals (Arctocephalus pusillus), sharks (15 species), sunfish (Mola mola) and cetaceans (two species). Temporal analysis revealed significant differences between day-time and night-time CPUE for nine species, and significant differences in seasonal CPUE for 17 species. Spatial analysis of small fauna species composition and of large fauna species composition identified three groups in each. The 100% observer coverage is high compared to other South African fisheries, and, although the average sampling rate of 1.56% is low, an increase in the sampling rate might not be feasible owing to the size of catches. The bycatch rate in this fishery is low compared to other South African trawl fisheries but similar to global midwater trawl bycatch rates. There are species overlaps with various fisheries, namely the demersal trawl, small pelagic, linefishery, shark longline and squid fisheries, yet the total catch estimates from this fishery are generally small relative to catches taken in the target fisheries. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/19999 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:31:47.142Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| 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:11427/19999 Bycatch in the South African midwater trawl fishery for horse mackerel (Trachurus capensis) as established from observer records Reed, Jodie Romay Attwood, Colin Kerwath Sven Applied Marine Science The South African midwater trawl fishery targets adult horse mackerel (Trachurus capensis) on the Agulhas Bank. The bulk of the catch is taken by a single midwater trawler. The bycatch of this fishery is investigated by analysing observer records from 2004 to 2014 to report on bycatch composition, volumes and temporal and spatial patterns. Small fauna were analysed by extrapolation of sample weights and large fauna were counted. The midwater trawl fishery was estimated to have caught 25 415 t annually, with a bycatch rate of 6.9% of the total catch, by weight. Bycatch species with the highest average annual catches were chub mackerel (Scomber japonicus), redeye roundherring (Etrumeus whiteheadi), ribbonfish (Lepidopus caudatus) and hake (Merluccius spp.). Large fauna bycatch species included Cape fur seals (Arctocephalus pusillus), sharks (15 species), sunfish (Mola mola) and cetaceans (two species). Temporal analysis revealed significant differences between day-time and night-time CPUE for nine species, and significant differences in seasonal CPUE for 17 species. Spatial analysis of small fauna species composition and of large fauna species composition identified three groups in each. The 100% observer coverage is high compared to other South African fisheries, and, although the average sampling rate of 1.56% is low, an increase in the sampling rate might not be feasible owing to the size of catches. The bycatch rate in this fishery is low compared to other South African trawl fisheries but similar to global midwater trawl bycatch rates. There are species overlaps with various fisheries, namely the demersal trawl, small pelagic, linefishery, shark longline and squid fisheries, yet the total catch estimates from this fishery are generally small relative to catches taken in the target fisheries. 2016-06-10T07:39:06Z 2016-06-10T07:39:06Z 2015 Master Thesis Masters MSc http://hdl.handle.net/11427/19999 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Applied Marine Science Reed, Jodie Romay Bycatch in the South African midwater trawl fishery for horse mackerel (Trachurus capensis) as established from observer records |
| thesis_degree_str | Master's |
| title | Bycatch in the South African midwater trawl fishery for horse mackerel (Trachurus capensis) as established from observer records |
| title_full | Bycatch in the South African midwater trawl fishery for horse mackerel (Trachurus capensis) as established from observer records |
| title_fullStr | Bycatch in the South African midwater trawl fishery for horse mackerel (Trachurus capensis) as established from observer records |
| title_full_unstemmed | Bycatch in the South African midwater trawl fishery for horse mackerel (Trachurus capensis) as established from observer records |
| title_short | Bycatch in the South African midwater trawl fishery for horse mackerel (Trachurus capensis) as established from observer records |
| title_sort | bycatch in the south african midwater trawl fishery for horse mackerel trachurus capensis as established from observer records |
| topic | Applied Marine Science |
| url | http://hdl.handle.net/11427/19999 |
| work_keys_str_mv | AT reedjodieromay bycatchinthesouthafricanmidwatertrawlfisheryforhorsemackereltrachuruscapensisasestablishedfromobserverrecords |