Stock assessment of the Chokka Squid : Loligo vulgaris reynaudii

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dc.contributor.advisorField, John G
dc.contributor.advisorButterworth, Doug S
dc.contributor.advisorCochrane, K L
dc.contributor.authorRoel, Beatriz Adelaida
dc.date.accessioned2016-05-11T08:06:45Z
dc.date.available2016-05-11T08:06:45Z
dc.date.issued1998en_ZA
dc.descriptionSummary in English.en_ZA
dc.descriptionBibliography: p. [199]-210.en_ZA
dc.description.abstractThe primary aim of the study was to assess the status and productivity of chokka squid. Main hypotheses examined are the following: that the sharp decline in the trawl fishery catch per unit effort (CPUE) data in the early 1980s, reflects a real decline in the trawlers catch rate; that the decline in the trawl CPUE index is caused by the jig fishery removing the biomass that otherwise would be available to the trawl fishery; that the jig fishery "disturbs" the spawning process and causes a decline in subsequent recruitment. Catch and effort data from the two fisheries, as well as biomass estimates from spring and autumn research surveys, were used. The two main fisheries and the catch and effort data are described. General Linear Modelling (GLM) was performed on the CPUE data from the trawl fishery in order to obtain annual indices of abundance. Further, results from a GLM analysis on two years of monthly jig CPUE data are presented. The dynamics of the stock biomass on the spawning grounds were modelled in order to assess the effects of current levels of effort and the existing closed season on the resource. The dynamics of the stock and the fishery were captured by a simple biomass-based model. Two dynamic methods were used to estimate model parameters: 1. a process-error estimator; 2. an observation-error estimator. All model parameter were estimated by maximum likelihood, and the corresponding confidence intervals were estimated by bootstrapping.en_ZA
dc.identifier.apacitationRoel, B. A. (1998). <i>Stock assessment of the Chokka Squid : Loligo vulgaris reynaudii</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/19576en_ZA
dc.identifier.chicagocitationRoel, Beatriz Adelaida. <i>"Stock assessment of the Chokka Squid : Loligo vulgaris reynaudii."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 1998. http://hdl.handle.net/11427/19576en_ZA
dc.identifier.citationRoel, B. 1998. Stock assessment of the Chokka Squid : Loligo vulgaris reynaudii. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Roel, Beatriz Adelaida AB - The primary aim of the study was to assess the status and productivity of chokka squid. Main hypotheses examined are the following: that the sharp decline in the trawl fishery catch per unit effort (CPUE) data in the early 1980s, reflects a real decline in the trawlers catch rate; that the decline in the trawl CPUE index is caused by the jig fishery removing the biomass that otherwise would be available to the trawl fishery; that the jig fishery "disturbs" the spawning process and causes a decline in subsequent recruitment. Catch and effort data from the two fisheries, as well as biomass estimates from spring and autumn research surveys, were used. The two main fisheries and the catch and effort data are described. General Linear Modelling (GLM) was performed on the CPUE data from the trawl fishery in order to obtain annual indices of abundance. Further, results from a GLM analysis on two years of monthly jig CPUE data are presented. The dynamics of the stock biomass on the spawning grounds were modelled in order to assess the effects of current levels of effort and the existing closed season on the resource. The dynamics of the stock and the fishery were captured by a simple biomass-based model. Two dynamic methods were used to estimate model parameters: 1. a process-error estimator; 2. an observation-error estimator. All model parameter were estimated by maximum likelihood, and the corresponding confidence intervals were estimated by bootstrapping. DA - 1998 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1998 T1 - Stock assessment of the Chokka Squid : Loligo vulgaris reynaudii TI - Stock assessment of the Chokka Squid : Loligo vulgaris reynaudii UR - http://hdl.handle.net/11427/19576 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/19576
dc.identifier.vancouvercitationRoel BA. Stock assessment of the Chokka Squid : Loligo vulgaris reynaudii. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 1998 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/19576en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Biological Sciencesen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherMarine Scienceen_ZA
dc.subject.otherMarine Biologyen_ZA
dc.titleStock assessment of the Chokka Squid : Loligo vulgaris reynaudiien_ZA
dc.typeDoctoral Thesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnamePhDen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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