Abstract

Growth, age and somatic production of the benthic predator Odontocymbiola magellanica were studied in Golfo Nuevo (42� S6 5� W), on the South American Atlantic shelf. Stable oxygen isotope ratios confirmed semiannual formation of internal and external shell growth marks. Mean shell length (SL) of females was 115 and 112 mm for males, while popu- lation modal shell-free wet mass (SFWM) was 62.8 g. A Gompertz growth function (SL¥ = 200 mm, K = 0.197, t0 = 5.486) fitted 113 pairs of size-at-age data (12 shells) best. O. magellanica is a long-lived species, reaching up to 20 years of age. The maximum individual somatic production of 29.3 g SFWM per year is attained at 145 mm SL, which corresponds to about 12 years of age. The life span of this volutid seems to be twice compared with other large gastropods. O. magellanica is a valuable and exploitable resource regarding its large size and somatic production, but on the other hand, its slow growth, late maturity and direct devel- opment makes it extremely vulnerable to overexploi- tation.

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