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 Karwar; 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.)
pelagic us. 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 103 boat days) which would
prevent overexploitation of the stocks of crabs in the coastal fishery sector of
Karnataka.