Variations in the fish catch composition in the Bay of St. Vincent, New Caledonia, as determined by experimental trawling

Abstract

An experimental trawl survey was conducted in the Bay of St Vincent between December 1984 and April 1986. In all, 85 hauls were performed during four cruises. The trawled fish represented 233 species and 59 families. Biomass and density estimates declined 13-fold between the first and last cruises. This decline is not due to the survey catch (less than 2% of the biomass of the bay), nor is it likely to be due to trawling-induced changes in habitat. Natural causes are the most likely reason for the decline. The r-type species (Leiognathidae, Lethrinus nematacanthus) had the largest population fluctuations, whilst longer living and later reproducing species (Saurida undosquamis, large Upeneus spp.) had the smallest. Trophic structure is studied using three expressions: number of species, biomass and density per trophic group. Number of species per trophic group was the most insensitive to changes in time and place, with density being the most sensitive. Study of the variations in trophic structure could help with the monitoring of major changes in fish populations caused by fishing or environmental changes.