Publication Abstract

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

B.A. Roel, K.L. Cochrane and J.G. Field

The trawl fishery, which targets Cape hake Merluccius spp. andAgulhas sole Austroglossus pectoralis, takes chokka squid Loligo vulgaris reynaudii asby-catch. Catch and effort data from the trawl fishery for the period 1978-1996 are usedto obtain annual estimates of catch rate (catch per unit effort cpue) for that period.Examination of the cpue trend shows a sharp decline in the early 1980s and, in order toidentify factors that could have influenced that decline, the distribution of fishingeffort is investigated both temporally and spatially. There is a possible change in theincidence of squid-directed catches over time, but their overall scarcity could have hadonly a small impact on the annual cpue trend. Further, using distribution of fishingeffort to evaluate the effects of possible changes in fishing patterns, rather thanchanges in resource abundance, on the trend in trawl cpue, it became clear that there hadbeen a contraction of the trawling grounds and changes in fishing patterns in relation todepth over time. Finally, a general linear model (GLM) is developed to quantify the effecton cpue of factors such as vessel characteristic, depth and position of the drag, seasonand target species, so obtaining a standardized trawl cpue index of chokka abundance.Analysis of that trend reveals a mean 7.7% annual decline for the period investigated,which should be interpreted as a strong sign of resource decline.

Reference:

B.A. Roel, K.L. Cochrane and J.G. Field, 2000. Investigation into the declining trend inchokka squid Loligo vulgaris reynaudii catches made by South African trawlers. SouthAfrican Journal of Marine Science, BI: 121-135.