Mortality and stock assessment of two marine portunid crabs, Portunus (Portunus) sanguinolentus (Herbst) and Portunus (Portunus) pelagicus (Linnaeus) along the southwest coast of India

Abstract

The stock assessment of the marine crabs, Portunus (Portunus) sanguinolentus and Portunus (Portunus) pelagicus exploited by the mechanised trawl fishery was made based on the data collected from the commercial catches landed at Mangalore, Malpe and Kanvar; three important fish landing centres in the Karnataka state along the southwest coast of India during 1992-'94 and the results presented. In P. (P.) sanguinolentus, the mean values of total mortality coefficient (Z), natural mortality coefficient (M) and fishing mortality coefficient (F) were 4.2 + 0.51, 1.6 and 2.6 for males and 3.9 + 0.42, 1.5 and 2.4 for females respectively. In P. (P.) pelagicus, the average values of Z, M and F were 5.6 + 0.71, 1.7 and 3.9 for males and 4.9 + 0.69, 1.6 and 3.2 respectively for females. The standing stocks were 308 tonnes for P (P.) sanguinolentus and 161 tonnes for P. (P.) pelagicus. The annual average stocks were 1,272 tonnes for the former species and 834 tonnes for the latter. The maximum sustainable yield (MSY) was 776 tonnes for P. (P.) sanguinolentus and 567 tonnes for P.(P.) pelagicus. Based on the results obtained, it is felt imperative to increase the cod end mesh size of trawl to 40 mm and also to restrict the level of effort at the present level (1,130 trawlers per day or 234 x lo3 boat days) which would prevent overexploitation of the stocks of crabs in the coastal fishery sector of Karnataka.