Instantaneous total mortality coefficent (Z) in Metapenaeus monoceros has been estimated from the length-frequency distribution estimated to annual catch for the years 1974-1977 for both males and females. The estimates of Z based on Heincke's method, Beverton and Holt method and cohort analysis are closer to each other. The estimates of Z by these methods indicate a gradual increase in the values from 1974 to 1977 corresponding to the increase in fishing effort. The estimates of Z obtained by cumulative catch-curve and catch-curve methods are closer to each other and higher than those obtained by the other three methods. Reasons for these variations are discussed. The estimates of natural mortality coefficient (M) by Cushing's method and Pauly's method are closer to each other. Based on the values of Z obtained by Beverton and Holt method (4.364 for males and 3.664 for females) and the values of M obtained by Cushing's method (2.42 for males and 2.22 for females) fishing mortality coefficient (F) is estimated as 1.944 for males and 1.444 for females during the years 1974-77.

Stock assessment by 'Surplus-yield' model and yield-per-recruit model as well as Baranov's catch equation and cohort analysis indicate that the stock is fished just at the optimum level of exploitation and any further increase in effort will reduce the catch per hour of trawling.