POPULATION-DYNAMICS OF THE BIVALVES GARI-SOLIDA, SEMELE SOLIDA AND PROTOTHACA-THACA FROM A SMALL BAY IN CHILE AT 36-DEGREES-S

Gari Solida (Gray, 1828), Semele solida (Gray, 1828) and Protothaca thaca (Molina, 1782) are dominant members of the shallow-water, soft-bottom communities of the Peruvian-Chilean upwelling system. They are exploited commercially all over their distribution range. Reproduction, growth, mortality, and production of these species were studied from a small bay in Chile at 36 degrees S. Results indicate an annual reproductive cycle with a short spawning season. The growth parameters of the non-oscillating von Bertalanffy function were: G. solida: L(infinity) = 89.6 mm, K = 0.307 yr(-1), t(0) = 0.354 yr(-1); S. solida: L(infinity) = 78.0 mm, K = 0.297 yr(-1), t(0) = 0.374 yr(-1); P. thaca: L(infinity) = 82.2 mm, K = 0.174 yr(-1), t(0) = 0.069 yr(-1). Production estimates agree very well with data of other members of the Tellinacea and Veneracea taken from the literature. Annual somatic and gonad production amounted to 27.6 and 56.0 (G. solida), 4.8 and 8.6 (S. solida) and 16.9 and 14.5 (P. thaca) g AFDW m(-2). The following production/biomass (P/(B) over bar) ratios were obtained: for G. solida 0.334, for S. solida 0.188 and for P. thaca 0.269. Total mortality was estimated as 0.842 (G. solida), 0.924 (S. solida) and 0.584 yr(-1) (P. thaca). The influence of latitudinal gradients on reproductive strategies is related to the results on reproduction cycles. Production and mortality estimates are discussed in relation to the influence of the fishery.