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 th aca (Molina, 1782) are dominant members of the shallow-water, soft-bot tom communities of the Peruvian-Chilean upwelling system. They are exp loited commercially all over their distribution range. Reproduction, g rowth, mortality, and production of these species were studied from a small bay in Chile at 36 degrees S. Results indicate an annual reprodu ctive 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(infini ty) = 78.0 mm, K = 0.297 yr(-1), t(0) = 0.374 yr(-1); P. thaca: L(infi nity) = 82.2 mm, K = 0.174 yr(-1), t(0) = 0.069 yr(-1). Production est imates agree very well with data of other members of the Tellinacea an d Veneracea taken from the literature. Annual somatic and gonad produc tion amounted to 27.6 and 56.0 (G. solida), 4.8 and 8.6 (S. solida) an d 16.9 and 14.5 (P. thaca) g AFDW m(-2). The following production/biom ass (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 rela ted to the results on reproduction cycles. Production and mortality es timates are discussed in relation to the influence of the fishery.