Composition, richness and characterization of the benthic community in a non-fished area at the Patagonian Scallop fishing grounds, Argentina

LAURA SCHEJTER; BREMEC CLAUDIA

Florianopolis

Workshop; 19th. International Pectinid Workshop; 2013

Introduction The Patagonian scallop Zygochlamys patagonica is a very important invertebrate marine resource exploited in Argentina since 1996. Management strategies were applied from the beginning of the fishery and included, among many other regulations, the annual monitoring of the benthic community by means of the by-catch assessment. The total fishing area of the Patagonian Scallop in the SW Atlantic Ocean (subdivided into smaller Management Units) is comprised between 36º43’ and 48º30’S, along the shelf-break frontal area, at depths ranging between 70 and 130 meters, approximately. During January 2011, exploratory cruises were developed in order to assess scallop biomass and benthic community composition at an area comprised in the middle of the fishing grounds area, but with few or no fishing records until 2011. The objective of the present contribution is the characterization of the benthic community in this unfished area and its comparison with nearby fished areas also comprised inside the Patagonian scallop fishing grounds of Argentina. Materials and Methods The non-fished study area (NFA) was located between 39º48’ and 41º05’S (currently Management Unit C). In total, 29 samples (Vol.:10L) were collected in the mentioned area in order to assess benthic community composition. For comparative purposes, we analyzed the composition of 22 samples in a northern area (FN) and 25 in a southern area (FS). These samples were taken during stock assessment cruises developed during 2010. All the samples were collected onboard fishery vessels equipped with non-selective bottom otter trawls with booms (100 or 120mm mesh size, depending on the vessel). Sampling design obeyed to Zygochlamys patagonica biomass evaluation purposes. In each sampling site, trawling activity was conducted for 10 minutes at an average speed of 4 knots. This is the standard procedure not only for monitoring cruises, but also during routine fishing of the scallopers. Once the capture was on the deck, a 10L subsample of the total catch (excluding fishes) was taken for the ecological studies. For the community composition study here developed, porifera, bryozoa and hydrozoa remained as major taxa. Results and Discussion Results showed that taxa richness in the NFA was higher than in the other 2 fished areas (see Table). Moreover, NFA samples presented also a higher number of taxa-per-site. Number of samples Taxa/site (range) Taxa richness/site (average) Total taxa richness FN 22 9-28 18,5 46 NFA 29 13-38 25,69 67 FS 25 9-29 18,6 60 However, the species composition and the assemblage in all the areas were similar. The NFA was characterized by a low scallop yield (in average, 22.88% considering total scallops and 18.44% for commercial scallops*) being the average biomass 27% of the total benthic community; presumably the reason why this area was not preferred by the commercial fleet since the beginning of the fishery. Contribution in biomass of sponges in the NFA is surprisingly high (average: 22%, although it could reach up to 90% in one site) and the main difference with the other two areas (3% and 6.71% in average in the FN and FS, respectively). Sponge species identified until moment are the same previously recorded for the shelf-break area by some authors of the present study, although this taxonomical study is still in progress and it is possible that additional species and new distributional records could be found.