Population dynamics of three commercially important bivalve species (Family: Veneridae) in Puttalam lagoon and Dutch bay, Sri Lanka

The present study was carried out to investigate the population dynamics of three bivalve species, viz, Gafrarium tumidum, Marcia hiantina and Marcia opima in Dutch bay and Puttalam lagoon, Sri Lanka, in order to make recommendations for sustainable exploitation of these resources. The growth performance index (Ø) for the three species calculated from asymptotic length and growth constant, which were estimated using Compleat ELEFAN software package, ranged from 3.19 to 3.48 in Dutch bay and from 3.18 to 3.40 in Puttalam lagoon. The slightly better growth performance in Dutch bay may be due to more favourable environmental conditions than in Puttalam lagoon.

In Dutch bay, M. hiantina and M. opima which were less abundant, were heavily exploited, as opposed to the most abundant G. tumidum, which was least exploited. Exploitation rates of G. tumidum, M. hiantina and M. opima were 0.30, 0.83, and 0.73 respectively. Two recruitment pulses occurred in the three bivalve populations in Puttalam lagoon while a single recruitment pulse occurred in Dutch bay. As such, the three bivalve populations in Puttalam lagoon appear to be "r - selected" while those in Dutch bay appear to be “K- selected". This study revealed that the three bivalve species occurring in Dutch bay could support a small-scale fishery.