Evaluation du stock de palourdes du bassin d'Arcachon

As part of a larger project financed by the European Union programme "Community initiative PESCA" on the study of "small scale fisheries" in Aquitaine (France), an estimation of the stock of clams in the Bassin d'Arcachon has been conducted. A two-stage stratified random sampling survey has been designed. Samples have been collected using a Hamon bottom sampler in 237 locations distributed over 24 km2. The clam Tapes philippinarum, which appeared in the basin following a series of aquaculture experiments in the mid eighties, is now the main species accounting for more than 90% of the abundance and the biomass, largely overcoming the European species Tapes decussata. The mean abundance and biomass (26 clams / m2 et l28g / m2) are above those estimated in other regions (Golfe du Morbihan and Etang de Thau) where similar studies have been conducted. Although this study does not cover the whole area of extension of the stock, the total biomass estimated is quite high with more than 2900 tonnes. The size distributions of Tapes philippinarum are in the range 8 - 42mm with a main mode around 28-30mm and the exploitable fraction of the stock (L >= 35 mm) is less than 10% in numbers and 23% (i .e. 690 tonnes) in biomass. This size distribution observed reflects probably a high exploitation rate and it is to be feared that a large proportion of small clams are present in the catch. Thus, an important recommendation would be to reduce the proportion of small clams in the catch. The closure of three areas decided from July 2000 should also allow the stock of exploitable biomass to rebuilt in those zones.