Seasonal growth, stock-recruitment relationship and predictive yield of the Indian squid Loligo duvauceli (Orbigny) exploited off Karnataka coast

Abstract

A seasonally oscillating version of the von Bertalanffy growth function was fitted to explain growth in the Indian squid Loligo duvauceli (Orbigny) exploited from the Arabian Sea off Karnataka State. The parameters estimated were L_ = 371 mm; K=1.4 yr'; C=0.5 and WP=0.56, considering that the AT (5°C) in annual mean seawater temperature is sufficient to induce small but significant oscillations in the growth pattern. A retrospective analysis of the data on squid fishery for 1983-'95 was done using length-structured virtual population analysis (VPA) and this indicated that the mean number of survivors was on an average 10 times more than the numbers caught. Further, nearly 6 % of the stock died due to natural causes annually, Ricker's stockrecruitment curve could adequately (R^=0.45) explain the variation in recruitment with respect to spawning stock biomass (SSB). The study indicated that squid SSB is a reasonably good predictor of its recruitment. Predictive yields were assessed using the Thompson and Bell model and it indicated an MSY level of 6,059 t and MSE of Rs. 270.3 million, while the present average catch (1990-'94) amounted to 5,157 t valued at Rs. 234.9 million. The MSY and MSE can be attained by reducing trawl effort to 44 % of the present effort.