Investigation into the declining trend in chokka squid Loligo vulgaris reynaudii catches made by South African trawlers

The trawl fishery, which targets Cape hake Merluccius spp. and Agulhas sole Austroglossus pectoralis, takes chokka squid Loligo vulgaris reynaudii as by-catch. Catch and effort data from the trawl fishery for the period 1978- 1996 are used to obtain annual estimates of catch rate (catch per unit effo rt cpue) for that period. Examination of the cpue trend shows a sharp decli ne in the early 1980s and, in order to identify factors that could have inf luenced that decline, the distribution of fishing effort is investigated bo th temporally and spatially. There is a possible change in the incidence of squid-directed catches over lime, but their overall scarcity could have ha d only a small impact on the annual cpue trend. Further, using distribution of fishing effort to evaluate the effects of possible changes in fishing p atterns, rather than changes in resource abundance. on the trend in trawl c pue, it became clear that there had been a contraction of the trawling grou nds and changes in fishing patterns in relation to depth over lime. Finally , a general linear model (GLM) is developed to quantify the effect on cpue of factors such as vessel characteristic, depth and position of the drag, s eason and target species, so obtaining a standardized trawl cpue index of c hokka abundance. Analysis of that trend reveals a mean 7.7% annual decline for the period investigated, which should be interpreted as a strong sign o f resource decline.