Structure of the soft bottom fish assemblages of the North Lagoon of New Caledonia.

The soft bottom fish communities of the North Lagoon of New Caledonia were studied by trawling. In all, 185 species belonging to 54 families were recorded. The density was 2.08 10(-2) fish/m(2) and the biomass was 8.29 10(-1) g/m(2). The communities were dominated by a small number of species, in particular Saurida undosquamis, Nemipterus peronii and Engyprosopon grandisquama. Three different communities were identified along an inshore-offshore gradient. They were characterized by different species associations and linked to depth, bottom characteristics and benthos. The first fish community (type A) was diversified but density and biomass were low. Lethrinus genivittatus, Upeneus sp.2 and Paramonacanthus japonicus characterized this assemblage. This community was found on the shallowest stations, with the less silted and coarsest sediment. On these stations, the megabenthos was rich and diversified. The second fish community (type B) was less diversified with low density and biomass. Synodus hoshinonis, Saurida undosquamis, Onigocia macrolepis et Nemipterus peronii characterized this assemblage. This community was found on the deepest stations where oceanic influence was the most important. The third fish community (type C) was diversified and density and biomass were the most important. Upeneus tragula was one of the fish species characterizing this assemblage. This community was found at intermediate depth silted stations where the megabenthos was scarce. These results give unique information on pristine fish communities. They confirm the importance of the links between the fish community structure, the biotope and benthos characteristics. These links could explain the shift in the fish species composition that had been recorded in several Indo-Pacific soft bottom trawl fisheries.