Diversity and Abundance of a Tropical Fishery on the Pacific Shelf of Michoacán, México

This study was undertaken on the Pacific coast of Mexico. Some 22 523 individual fish were sampled, representing two classes, 154 genera, 64 families and 257 species in a total area of 50 km2. The speciesLutjanus guttatus, Scomberomorus sierra, Cynoscion reticulatus, Sphyrna lewini, Arius platypogonandCaranx caninuswere the most numerically abundant, amounting to 53•2% of the whole sample. Two models for sample size analysis and richness prediction were used. From these, the forecast for a theoretical doubling of the level of sampling effort (90 days) was 297 and 331. The Shannon diversity indexes in summer (June–August) and winter (December–February) were significantly different (pairedt-test,P<0•0005). Of four families compared, three gave significant differences in the summer and winter periods (the Carangidae, the Haemulidae and the Sciaenidae). The classification (Euclidean Distance and UPGMA) indicated two climatic periods and three species assemblages. In addition, the nodal fidelity analysis agreed with the importance of the winter season in the study area. Two El Niño/southern oscillation incidences from 1986–87 and 1991–93 occurred during the sampling period.