Growth and population dynamics of short-neck clam Paphia malabarica from Dharmadom estuary, North Kerala, southwest coast of India

Abstract

Growth and population dynamics of the short-neck clam Paphia malabarica from Dharmadom estuary in north Kerala was studied for one year (December 2003-November 2004). The age and growth of P. malabarica were studied by continuous sampling of the population and analyzing the changes in size frequency distribution. The growth parameters of the von Bertalanffy growth function was L∞ = 59 mm, annual K= 0.92, and t0 = -0.1596. The life span was estimated as 2.5 to 3 years. P. malabarica in the estuary attains a length of 35.5 mm and 49.6 mm respectively at the end of the first and second year. The length at first maturity (Lm) was estimated as 22 mm and 50% of the clams matured at the age of 7 months. All the clams above 22 mm were mature i.e., before reaching the first year. The total mortality coefficient (Z) was 4.65, natural mortality coefficient (M) was 1.82 and fishing mortality coefficient (F) was 2.83. Virtual Population Analysis showed that F was the maximum in the largest size group (35– 38 mm). The mean numbers and catch by length showed that the maximum catch (16.5 t) consisted of 35-38 mm length group. Average yield of P. malabarica for the period 2003-2004 calculated from the length-based Thompson and Bell prediction model was 115 t and the maximum sustainable yield (MSY) was 69.3 t. It was found that 80% of the present effort is sufficient to arrive at the MSY.