Seasonal and spatial variation in the abundance and size distribution of fishes associated with a petroleum platform in the northern Gulf of Mexico

Abstract

Stationary dual-beam hydroacoustics and visual point count surveys were used in tandem to measure the density, target strength, and species composition of fishes associated with a petroleum platform in the northern Gulf of Mexico. Fish densities ranged from 0 to 10.5 fish m^-3 during monthly sampling trips from January 1991 to May 1992. Density and target strength were spatially and temporally variable. Target strengths varied significantly with side of the platform, month, and east and north current vectors. Density varied significantly with platform side, month, east current vector, and depth. Density and target strength did not change over 24 h periods or with water temperature. Fish densities were highest adjacent to the platform and decreased significantly beyond 16 m. Approximately 1990 - 28,100 fish were associated with the platform depending on the month. A total of 19 species were observed at the platform, with Chaetodipterus faber, Caranx fusus, Seriola dumerili, Balistes capriscus, Lutjanus campechanus, and Archosargus probatocephalus constituting 97% of observed fishes. Based on our results, we conclude that the fishes associated with a petroleum platform conform with the open nonequilibrium hypothesis proposed for fishes in coral reef habitats.