Population dynamics of the squid Loligo duvaucelii D'orbigny (Cephalopoda) in Saurashtra waters

Age and growth, gear selection, instantaneous total mortality co-efficient (Z) and instantaneous natural mortality co-efficient (M) were estimated for the squid Loligo duvaucelii from catch, effort and length frequency data collected from trawl net operations at Veraval from 1979 to 1983. Estimated yield per recruit at different combinations of age at first capture, fishing mortality co-efficient (F) and cod end mesh size are given in the form of yield isopleth diagrams for two different M/K ratios. Optimum effort was found to be just higher than the present average effort expended indicating that the squid fishery does not presently suffer from overfishing. For better management of this fishery, it is observed that the prevailing mesh size be increased to 35 mm so as to realise higher yield and to cope with the impending increase in effort. This observation is valid only when the fishery is aimed mainly at L. duvaucelii as the squid is only a by-catch in the trawl net