COMPARISON OF FISH ASSEMBLAGES SAMPLED BY A SHRIMP TRAWL AND A FISH TRAWL, IN ST-VINCENT BAY, NEW-CALEDONIA

The spatial and temporal patterns of variation of a tropical soft-bott om fish community sampled by a shrimp trawl and a fish trawl were comp ared at two sites, North and South Bay, of St Vincent Bay, New Caledon ia. Results indicated that the species richness and particularly the s pecies composition were related to the type of trawl. However, the ove rall density and biomass, species diversity, and evenness did not vary significantly as a function of gear type. The same species dominated the catches of the two trawl types, but differences appeared between d ensity, biomass and mean weight of particular species, calculated from the shrimp and the fish trawl catches. The spatial variations of the community structure were comparable between the two gear types, though the composition of the species assemblages were not the same. Differe nces appeared for the temporal structures. These differences were insi gnificant in one of the sampled sites (North Bay), but more important in the other site (South Bay), where species diversity, size range of the individuals, and shape diversity of fishes were more important. Ho wever, the major differences between the community structures remained the same, independent of sampling gear type. These results validate s tudies comparing spatial and temporal patterns of variations in genera l characteristics (i.e. number of species per haul, density, biomass, species diversity and evenness) of tropical soft-bottom fish communiti es determined by shrimp and fish demersal otter trawls. This also vali dates the determination of species assemblages especially spatial asse mblages. However, important problems may arise when more particular po ints are studied, such as species composition of the communities, dete rmination of the characteristic species of the assemblages, or study o f a particular species. In such studies, the use of several different trawl types, which give a substantially enlarged perspective of the co mmunity, is an alternative.