Reproductive biology and ecology of Adelomelon brasiliana (Mollusca:Gastropoda) off Buenos Aires, Argentina.

Abstract

A. brasiliana is an abundant shallow water volutid distributed from Río de Janeiro, Brazil, to Río Negro, Argentina, SW Atlantic. This species has been commercially exploited in Uruguay by small-scale fishery since the early 90 s. In Argentina is still not systematically exploited. The reproductive biology, and some of the ecologically important aspects of this volutid have been studied at Mar del Plata, Argentina (38° 20 S; 57° 37 W). The reproductive season extends from September to April, showing synchronization with the water temperature cycle. Modal shell length (SL) of the population was 140 mm, while modal shell free wet mass was 255 g. A logistic growth function (SLmax= 186.28 mm, K = 0.185, t0 = 4.601) fitted 131 pairs of size-at-age data (25 shells) best. Somatic production of the individuals (Pi) increased up to 46 g*year-1 (SFWM) at 145 mm shell length, which occurred in the 12th year of life. A. brasiliana has a very long life-span, living for up to 20 years of age. Minimum size for gonad maturity for females was 107 mm (males: 102 mm) in shell length, whereas 50% of the females were mature at 115 mm (males: 107 mm) SL (approx. 7 years of age). All females were mature at 125 mm (males: 115 mm) SL (up to 8 years of age). Imposex penis development in females- was found in over 30 % of the females in the sampled period, however the relative penis size index (RPSI) was very low and the functionality of the reproductive system was not affected. TBT in soft parts decreased from 46 ng/g to 21 ng/g in the study period, while in the sediment it decreased from 240 ng/g to 1.4 ng/g TBT, indicating a major pollution event before the start of the study. A. brasiliana is a species with a long life span, slow growth rate and long maturation size. These features make this species very vulnerable to exploitation. Accurate management rules are needed before starting commercial exploitation, being also very sensitive to pollution.