Fishery and population dynamics of two species of carangids, Decapterus russelli (Ruppell, 1830) and Megalaspis cordyla (Linnaeus, 1758) from Mumbai waters

The population parameters viz., growth, mortality, exploitation ratio and length at first capture of Decapterus russelli and Megalaspis cordyla from Mumbai waters were investigated to derive requisite information for their effective management. The von Bertalanffy growth equations were derived as Lt = 25.6 cm [1-exp {-0.95 year-1 (t-(-0.00095))}] for D. russelli and Lt = 46.8 cm [1-exp {-0.55 year-1(t-(-0.00386))}] for M. cordyla. The annual total instantaneous mortality (Z), natural mortality (M) and fishing mortality (F) were assessed as 4.61, 1.81 and 2.8 for D. russelli and 1.79, 1.07 and 0.72 for M. cordyla respectively. The size at first capture was estimated as 15.78 cm for D. russelli and 25.80 cm for M. cordyla . The exploitation ratio (E) was found to be beyond the optimum level for D. russelli (0.61) while it was below the optimum for M. cordyla (0.40). The average annual MSY estimated was nearly 31 t against the present average annual yield of about 37 t for D. russelli , whereas for M. cordyla , the MSY was higher than the present yield. The results indicate that there is a threat of stock depletion of D. russelli in Mumbai waters.