Stock assessment and management options for whelks along south-eastern Arabian Sea

Abstract

Two species of whelks viz., Babylonia spirata and Babylonia zeylanica belonging to the family Buccinidae are commercially fished from Kollam, south-west coast of India, since early 1990’s and are exported from India under the trade name ‘Baigai’. The species is present all through the year in the fishing grounds, caught as by-catch in shrimp trawlers and is a targeted fishery from April to June, when more than 50% of the annual whelk catch is taken. B. zeylanica dominates the whelk catch (61% of the annual catch). The average catch rate in the modified trawlers for whelk was 400 kg unit-1 day-1. Following the von Bertalanffy growth function, asymptotic length and growth rate were estimated as 68.7 mm and 1.08 respectively for B. spirata and as 76 mm and 1.15 respectively for B. zeylanica. The L50 estimated for B. spirata and B. zeylanica were 35.2 and 41.7 mm respectively. The optimum length of capture and mean generation time were 40 mm and 0.55 years for B. spirata and 44 mm and 0.48 years for B. zeylanica respectively. The annual mean length of B. spirata showed an increase from 37.4 mm in 2001 to 40.1 mm in 2002 and multiple cohorts have been observed. The relative yield-per-recruit analysis shows that, present rate of exploitation of B. spirata has reached the optimum and that of B. zeylanica has nearly attained the optimum. The faster growth rate, early maturity and continuous breeding behaviour explain the sustained fishery of B. spirata and B. zeylanica under a high fishing pressure along Kollam coast.