The Gulf of California has rocky reefs that shelter about 271 species of fish. Previous studies on this fauna have been scarce and regional in coverage or small spatial scale studies. La Paz region has great interest for ornamental fishing and sport diving industries. Therefore, this
study was aimed to investigate the spatial and temporal patterns of reef fish diversity. Sampling was carried out by scuba diving visual censuses at six sites in the region of La Paz, Baja California Sur, Mexico. Timed transects made in the four seasons of 1995, at two depths (6 and 12 m),
found 80 species of fish from 31 families. The number of species was significantly different for each reef and depth. Los Islotes had the highest number of species. According to the Index of Biological Value, 20 species were dominant for all reefs, but the relative importance of each varied
by reef, season, and depth. There were significant differences of diversity both between depths and reefs. There was a latitudinal gradient of diversity, increasing from north to south. Grouping analysis showed three well-defined environments: exposed, sheltered, and 'special' reefs.
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