Biology and fishery of the whelk Buccinanops globulosum (Kiener, 1834) in northern coastal waters of the San Matías Gulf, Patagonia, Argentina

The whelk Buccinanops globulosum, a very common prosobranch mollusk in northern Patagonian, is the target of a new fishery in San Matías Gulf. Given certain biological characteristics making this species susceptible to overfishing, a study started in 2000 in order to collect data on demography and growth at age of this species, with the aim to design and to implement a provisional management plan.

Mean density was estimated at 111 individuals m−2 (S.D. = 16.77). Females outnumbered males in most of the months (P < 0.05) and appeared laying egg capsules from November to January. The smallest female carrying egg capsules was 45.2 mm total conch length (n = 36). Recruitment peak was identified in January 2002 and January–February 2003. Early crawling juveniles had a mean size of 4.2 mm conch length (S.D. = 0.51, n = 60).

A total of 450 individuals (263 females and 187 males) were examined for growth at age. Significant differences were found in the growth parameters between sexes (maximum likelihood method; χ = 92.34; gl = 3; P < 0.001). Growth of males was lower than growth of females.

Commercial capture of whelks is done by diving using a bait of fish discarded or open living purple clams. Only adults up 4 cm are retained during the fishing operations in a net bag. During 2000–2004 the annual catch varied from 20 to 9200 kg. Fluctuations in landings have more often reflected market prices rather than changes in the abundance of the resource. If effort for this whelk increases it should be necessary to consider a period of no fishery at all in the reproductive/recruitment period in order to ensure the sustainability of the stock.