Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Migrations of spiny rock-lobsters, Jasus Lalandii, at Luderitz : environmental causes, and effects on the fishery and benthic ecology
Includes bibliographical references.
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
Department of Biological Sciences
2014
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613212317319169 |
|---|---|
| access_status_str | Open Access |
| author | Tomalin, Bruce John |
| author2 | Branch, George M |
| author_browse | Branch, George M Tomalin, Bruce John |
| author_facet | Branch, George M Tomalin, Bruce John |
| author_sort | Tomalin, Bruce John |
| collection | Thesis |
| description | Includes bibliographical references. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/9665 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:32:33.381Z |
| 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:11427/9665 Migrations of spiny rock-lobsters, Jasus Lalandii, at Luderitz : environmental causes, and effects on the fishery and benthic ecology Tomalin, Bruce John Branch, George M Zoology Includes bibliographical references. A dispute arose in the Luderitz rock-lobster, Jasus lalandii, fishery as to whether declines in CPUE were due to changes in rock-lobster migration patterns or a reduction in fishable biomass. Rock-lobster migrations were studied at two sites by estimating in situ density in the 10-12m and 15-20m depth zones. Water temperature and dissolved oxygen concentration profiles were obtained at several sites at approximately monthly intervals. Observations over a period of six years indicated that rock-lobster underwent seasonal in- offshore migrations and that marked interannual variation in those migration patterns did, indeed, occur. The movements and their interannual variation were directly related to the inshore presence of water with very low dissolved oxygen concentrations. CPUE was closely related to the density of legal sized rock-lobster on the fishing grounds (observed by SCUBA diving) and hence it is feasible that at least a part of the decline in CPUE at Luderitz was due to an alteration in the "normal" pattern of in-offshore migration. The hypothesis that environmental change caused the major decline in rock-lobster catches at Luderitz was examined by time series analysis of 21 years of CPUE, wind, SST and sea-level data. Luderitz rocklobster CPUE was found to be negatively correlated with the southerly component of summer wind stress at Diaz Point six years previously. On this basis it was hypothesised that variable settlement of puerulus larvae is an important factor driving changes in recruitment to the fishable population. The mechanism may be increased mortality of larvae as they attempt to cross the continental shelf (due to greater northward and offshore drift during periods of strong southerly wind). The dramatic interannual changes in rock-lobster density provided an opportunity to carry out a "natural" experiment on the interaction between rock-lobsters and the associated benthic species assemblage. It was found that, although there were changes in the benthos (notably an increase and subsequent decline in whelk density), these were unrelated to variation in rock-lobster density. In addition, no relationship between per capita food availability and rock-lobster growth on four grounds, was apparent. As regards temporal changes in food supply and subsequent effects on rock-lobster growth rates; there was no temporal reduction in food supply at the main study site which could be related to the reduction in CPUE since 1988. 2014-11-15T19:43:37Z 2014-11-15T19:43:37Z 1993 Master Thesis Masters MSc http://hdl.handle.net/11427/9665 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Zoology Tomalin, Bruce John Migrations of spiny rock-lobsters, Jasus Lalandii, at Luderitz : environmental causes, and effects on the fishery and benthic ecology |
| thesis_degree_str | Master's |
| title | Migrations of spiny rock-lobsters, Jasus Lalandii, at Luderitz : environmental causes, and effects on the fishery and benthic ecology |
| title_full | Migrations of spiny rock-lobsters, Jasus Lalandii, at Luderitz : environmental causes, and effects on the fishery and benthic ecology |
| title_fullStr | Migrations of spiny rock-lobsters, Jasus Lalandii, at Luderitz : environmental causes, and effects on the fishery and benthic ecology |
| title_full_unstemmed | Migrations of spiny rock-lobsters, Jasus Lalandii, at Luderitz : environmental causes, and effects on the fishery and benthic ecology |
| title_short | Migrations of spiny rock-lobsters, Jasus Lalandii, at Luderitz : environmental causes, and effects on the fishery and benthic ecology |
| title_sort | migrations of spiny rock lobsters jasus lalandii at luderitz environmental causes and effects on the fishery and benthic ecology |
| topic | Zoology |
| url | http://hdl.handle.net/11427/9665 |
| work_keys_str_mv | AT tomalinbrucejohn migrationsofspinyrocklobstersjasuslalandiiatluderitzenvironmentalcausesandeffectsonthefisheryandbenthicecology |