SEASONAL AND SPATIAL VARIATION IN THE ABUNDANCE AND SIZE DISTRIBUTIONOF FISHES ASSOCIATED WITH A PETROLEUM PLATFORM IN THE NORTHERN GULF-OF-MEXICO

Stationary dual-beam hydroacoustics and visual point count surveys wer e used in tandem to measure the density, target strength, and species composition of fishes associated with a petroleum platform in the nort hern Gulf of Mexico. Fish densities ranged from 0 to 10.5 fish.m(-3) d uring monthly sampling trips from January 1991 to May 1992. Density an d target strength were spatially and temporally variable. Target stren gths varied significantly with side of the platform, month, and east a nd north current vectors. Density varied significantly with platform s ide, month, east current vector, and depth. Density and target strengt h did not change over 24 h periods or with water temperature. Fish den sities were highest adjacent to the platform and decreased significant ly beyond 16 m. Approximately 1990 - 28 100 fish were associated with the platform depending on the month. A total of 19 species were observ ed at the platform, with Chaetodipterus faber, Caranx fusus, Seriola d umerili, Balistes capriscus, Lutjanus campechanus, and Archosargus pro batocephalus constituting 97% of observed fishes. Based on our results , we conclude that the fishes associated with a petroleum platform con form with the open nonequilibrium hypothesis proposed for fishes in co ral reef habitats.