Spatial variation of the abundance of the soft-bottom fauna on the continental shelf off Jalisco and Colima, Mexico (spring 1995)

Abstract

Spatial distribution of the abundance of the soft-bottom fauna was investigated through a survey with shrimp trawl nets. Differences in mean abundance indexes between sites were found, but the cause for these was not determined. Mean abundance indexes changed with depth, probably due to changes in the temperature of the water near the bottom. At the depth of 60 m, a high number of small fishes, mainly of the families Batrachoididae, Scorpaenidae and the order Pleuronectiformes, were found. At 20 and 40 m, a lesser mean number of individuals but a higher total weight per unit area were found as a consequence of the predominance in these levels of species with a higher mean individual weight, such as those of the family Diodontidae and the order Rajiformes. Invertebrates had a more uniform size throughout the depth gradient and were more abundant at the depth of 60 m. The species of the family Portunidae were dominant.