Quantitative and qualitative assessment of exploitation of juvenile cephalopods from the Arabian Sea and Bay of Bengal and determination of minimum legal sizes

Abstract

Using the minimum size at maturity (MSM) as a biological reference point and relatively low reproductive loads and generation times of the studied animals, the minimum legal sizes (MLS) for the Indian squid Loligo duvauceli, the pharaoh cuttlefish Sepia pharaonis and for the webfoot octopus Octopus membranaceous was fixed at 80, 115 and 45 mm Dorsal Mantle Length (DML) respectively with corresponding minimum legal weights at 25, 150 and 15 g. For L. duvauceli, during 1997-2001, 12.8% of the average catch was constituted by juveniles, the proportion being higher along the west coast. In 2002-05, the proportion of juveniles was lower at 5.3% and the total weights were also much less (1817 t as compared to 5354 t). In the case of S. pharaonis, 6.9% (2281 t) of the catch was constituted by juveniles, but the proportion was very high (22.4%) along the east coast. In O. membranaceous during 2002-04, an estimated 527 t (5.9%) of the total catch comprised of juveniles. The present Lmean in the fishery is lower than the Lopt and their difference is considerably high at 60 mm for L. duvauceli. However, in the case of S. pharaonis this difference is only 10 mm and in the case of O. membranaceous the Lmean is higher than the Lopt. If the juveniles are permitted to grow to Lmean by implementing the MLS, the estimated economic gain is to the tune of Rs. 426 crores per annum. The present study shows that harvest weights can be improved by up to 34 times and would result in higher incomes to trawl fishers.