SPATIAL VARIATION OF THE ABUNDANCE OF THE SOFT-BOTTOM FAUNA ON THE CONTINENTAL-SHELF OFF JALISCO AND COLIMA, MEXICO (SPRING 1995)

Spatial distribution of the abundance of the soft-bottom fauna on the continental shelf: off Jalisco and colima (Pacific coast of Mexico) wa s investigated through a survey with shrimp trawl nets. Samples were t aken at seven sites with mean depths of 20, 40, 60 and 80 m during Map and June 1995. Abundance indexes are given as number of individuals a nd total weight per unit of area swept in hectares. The values obtaine d showed a very high variance, with ranges from 30 to 1,952 ind/ha and 0.6 to 110.3 kg/ha for the fishes, and from 121 to 6,536 ind/ha and 1 .0 to 64.5 kg/ha for the invertebrates. Differences in mean abundance indexes between sites were found, but the cause for these was not dete rmined. Mean abundance indexes changed with depth, probably due to cha nges in the temperature of the water near the bottom. Al the depth of 60 m, a high number of small fishes, mainly of the families Batrachoid idae, Scorpaenidae and the order Pleuronectiformes, were found. At 20 and 40 m: a lesser mean number of individuals but a higher total weigh t per unit area were found as a consequence of the predominance in the se levels of species with a higher mean individual weight, such as tho se of the family Diodontidae and the order Rajiformes. Invertebrates h ad a more uniform size throughout the depth gradient and were more abu ndant at the depth of 60 m. The species of the family Portunidae were dominant.