Population structure and seasonal variation of molluscs associated with the artisanal lobster fishery in the Tropical Pacific

Mollusks associated to the spiny lobster fishery during 1997-1998 in the Tr opical Pacific were surveyed. A total of 1 081 specimens of 11 species were collected. The greatest captures were in autumn 1997 (28.16%) and summer 1 998 (25.58%). Dominant species were Hexaplex nigritus (Philippi 1845) (83.1 0%), Chi coreus regius (Swainson 1821) (8.04%), Vasum caestus (Broderip 183 3) (2.12%), C. brassica (Lamarck 1822) (1.85%) and C. erythrostomus (Swains on 1831)(1.75%), which have commercial importance. Weight-height ratio, sex ratio and height frequency histograms were done for dominant species. Sex ratio was 1:1, except for C. erythrostomus and H. nigritus (2 males:1 femal e); C. regius, C. erythrostomus and V. caestus presented an allometric grow th while H. nigritus and C. brassica grew isometrically. Only H. nigritus m ales were larger than conspecific females. There were significative differe nces in species distribution in relation with depth; C erythrostomus occurr ed in deepest layers while H. nigritus was more superficial; H. nigritus si ze differed with depth, temperature and locality.