Fish stock assessment of the northern New Caledonian lagoons: 2 - Stocks of lagoon bottom and reef-associated fishes

Fish stocks found on lagoon bottoms and near reefs are characterized by a h igh diversity and heterogeneous habitat which make stock estimation difficu lt. In particular, it is necessary to combine several methods in order to e valuate the major components of these stocks. The present study aimed at es timating reef fish stocks in the Northern Province of New Caledonia, a regi on where they represent a major target for the local fishermen. These estim ates were based on experimental fishing with handlines and bottom longlines . Handlines were used to assess the stocks near reefs, and longlines for th ose in areas away from reefs and on lagoon soft bottoms. Handline stations (363) were sampled in three different regions (west, north and east lagoons ) and three biotopes (nearshore, middle lagoon and barrier reef). A total o f 104 species were caught, the major families being Lethrinidae, Lutjanidae and Serranidae. Species composition and catch per unit of effort (CPUE) va ried among regions and biotopes. In particular, the north zone showed chara cteristics of an unexploited area with very high yields. An increase in CPU E and fish size from the coast towards the barrier reef and with increasing depth was observed in all regions. Correlations between CPUE from handline s and the numerical density and biomass estimates from underwater visual ce nsuses (UVC) performed on nearby reefs were significant. A total of 206 lon gline stations were sampled in the west and east regions. A total of 80 spe cies were caught, the major families being the same as those caught in stat ions with handlines with the addition of Carangidae. The CPUE of longlines was significantly correlated with numerical density and biomass estimates m ade by UVC along the longlines. Stock estimates based on the correlations b etween CPUE from handlines or longlines and UVC estimates indicate that 90 % of the lagoon stock were found on soft bottoms and near reefs. Reefs, des pite biomasses that were five times larger than soft-bottom and near-reef a reas, made only a small contribution to total stock. The ratio between dens ity and CPUE was highest for the lowest densities, thus indicating that fis hing efficiency increased with density. Comparison of handline catch perfor med around reefs and UVC data from nearby reefs suggests that there were st rong relationships between the fish assemblages of these two biotopes. (C) 2000 Ifremer/Cnrs/Inra/Ird/Cemagref/Editions scientifiques ct medicales Els evier SAS.