Stock assessment of the Chokka Squid : Loligo vulgaris reynaudii

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.

Grantor dc:publisher.institution

Department of Biological Sciences

Year dc:date.issued

1998

Author dc:creator

• Roel, Beatriz Adelaida

Advisors dc:contributor.advisor

• Field, John G
• Butterworth, Doug S
• Cochrane, K L

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/19576

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/19576