Optic-acoustic Analysis of Fish Assemblages at Petroleum Platforms

Petroleum platforms provide high-relief reef habitat in several ocean basins and are important to fishes and fishers alike. To determine which variables were important for shaping platform-associated fish assemblages on a basin-wide scale in the U.S. Gulf of Mexico, we employed optic and acoustic methods to measure fish distribution (geographic and water-column), abundance, biomass, density, size, diversity, and richness at 54 platforms. We found that variables related to freshwater inflow and meso-scale circulation patterns (e.g., salinity) affected more metrics than platform characteristics (e.g., platform depth). Platform fish assemblages varied gradually along gradients of these variables instead of exhibiting distinct assemblage groupings in non-metric multidimensional scaling space. These effects contributed to the presence of biomass, density, diversity, and richness "hotspots" at platforms offshore of the Atchafalaya River. Our findings underscore the importance of freshwater inflow and circulation patterns in explaining variation in reef fish assemblages in the U.S. Gulf of Mexico.