Limited gastropod abundances call for selective, small scale artisanal fisheries in a Patagonian marine protected area

Abstract

Marine gastropods are key items in small-scale fisheries worldwide, generating employment and high economic value in international markets. In North Patagonian Gulfs (Southwestern Atlantic), gastropods are landed as by-catch in bivalve artisanal fisheries, and thus no official statistics are reported. Recently, the first regulation of marine gastropod catches was established based on size at maturity for some edible species. However, additional biological-fishery data are necessary for developing a management plan if a regulated small-scale fishery is to be established. We provide the first preliminary estimation of the harvestable stock and other basic biological parameters of gastropods in the San José Gulf (SJG), a Natural Protected Area in Northern Patagonia. Density assessments are usually carried out using dredges or trawl nets that damage marine substrata, and thus we used data from non-destructive, drifting underwater visual census in transects, integrated with a Geographic Information System. We estimated the biomass, density, CPUE and the harvestable stock of Odontocymbiola magellanica and Buccinanops cochlidium, the main species currently landed in SJG. Visual surveys were conducted in 85,000 m2, where both species were present in depths ranging from 5 to 20 m depth. For O. magellanica, the maximum densities were 0.02–0.04 individuals m−2 with maximum CPUE of 12.8 kg diver−1 15 min−1 and estimated harvestable biomass of 837.05 kg (S.D. = 189.96), whereas for B. cochlidium densities were 0.32–0.60 individuals m−2 with maximum CPUE of 9.25 kg diver−1 15 min−1 and 365.12 kg (S.D. = 81.86) of harvestable biomass. The delayed maturity and reproductive strategies of both species, among other biological parameters, require a precautionary approach. The total exploitable biomass estimated in our work clearly highlights the need for a very selective, small-scale fishery, operating under a well enforced management plan regulating their capture to ensure its sustainability in a Natural Protected Area.