A general approach to length-weight relationships for New Caledonian lagoon fishes
Most studies involving Pacific reef fishes use underwater visual censusing techniques to estimate their biomass and stock. This requires to know the length-weight relationships of all the species censused. Currently, only a small proportion of these relationships (15.4%) are available for reef fish species in the Pacific area. In the present article we propose length-weight relationships at four organisation levels: species, genera, families and morphological groups. A data base of 53,800 specimens belonging to 788 species from New Caledonia were used to estimate the relationships for 396 species, 185 genera, 75 families. At the genus level, the length-weight relationships cover 76% of the Pacific reef species and the coverage is nearly 85% at the family level. A study of the morphology of 1,100 specimens belonging to 311 species allowed to define 30 morphological groups, for which length-weight relationships were then estimated using 32,551 specimens belonging to these species. Using 3 classes of body thickness, a second clustering of these species defined 20 groups allowing length-weight relationships to be estimated from 2D pictures. These relationships allow to estimate weight from length data for most of the species not covered by the relationships at the species, genus or family level. The error levels increase from the species (average error 9.4%) to the family level (13.5%), the morphological groups yielding errors equivalent to those from the family level equations (13.2%). A graphical analysis of the coefficients from 396 length-weight relationships suggests that there are physical limits to fish shapes.