Differential distribution pattern of native Ruditapes decussatus and introduced Ruditapes philippinarum clam populations in the Bay of Santander

Abstract

The aim of the present study is to provide a first characterization of the grooved carpet shell clam Ruditapes decussatus (native) and the Manila clam Ruditapes phillippinarum (nonindigenous) populations in the Bay of Santander in order to improve the management of these commercially exploited resources. For this purpose a field survey was carried out in different fishing areas where samples were taken on transects, following artisanal shellfisher exploitation techniques. Biometric relationships, size frequency distributions, densities and stocks were evaluated for different fishing zones. In addition, a hydrodynamic model was applied in order to understand larval transport and recruitment patterns associated to the tidal currents and water flow. Within this context, the first evaluation of the clam populations in the Bay of Santander showed: (a) that fishing activity is performed on individuals under the minimum legal size (40 mm) and in closed areas, (b) a significant differences on density by zone (c) a distribution pattern with areas where both species coexist and areas where one of them dominates, (d) R. decussatus occurs at relatively low density in stations near the culture parks and (e) a limited recruitment in the inner parts of Cubas tidal fresh for R. phillippinarum and in the southern zones for R. decussatus. Based on this study, some managing guidelines are presented mainly focused on avoiding the overfishing of the native clam R. decussatus.