Population dynamics and fishery of the fresh-water clam Polymesoda solida (Corbiculidae) in Cienaga Poza Verde, Salamanca Island, Colombian Caribbean

The fresh-water clam Polymesoda solida (Philippi, 1846) is the principal fi shery resource in the Cienaga Poza Verde, Salamanca Island, Colombian Carib bean Sea. Between July 1995 and June 1996, samples were taken to study repr oduction, growth, mortality, production and fishery aspects of this populat ion. P. solida is monoecious (hermaphroditic) combined with protogyny. We f ound an arrhythmic reproductive cycle with several spawning events per year , which could be related to the salinity cycle. The growth parameters of th e von Bertalanffy growth equation were: L-infinity = 47.3 mm and K = 0.204 yr(-1). The following mortality rates were estimated: total mortality, Z = 0.748, mean natural mortality, (M) over bar = 0.210 and fishing mortality F = 0.538 yr(-1). Somatic production of the population (in g AFDW m(-2) yr(- 1)), and the productivity(P/(B) over bar) were 0.647 and 0.230 respectively . P. solida is exploited in an artisanal (small-scale) fishery by approxima tely 80 fishermen. During the study period, mean daily catch was calculated as 314.4 kg shell free wet weight, and mean effort as 42 fishermen per day . Maximum exploitation rate, corresponding to the maximum relative yield pe r recruit and calculated with the relative yield per recruit model of Bever ton and Holt, was E-max = 0.445. The observed exploitation rate (E = 0.719) , calculated from fishing mortality, F and total mortality, Z, indicates ov erexploitation. A reduction of the fishing effort therefore is strongly sug gested, to achieve a sustainable exploitation. (C) 1998 Published by Elsevi er Science B.V. All rights reserved.