Method for estimating relative abundance and species composition around oil and gas platforms in the northern Gulf of Mexico, U.S.A.

Abstract

We used hydroacoustics and video data collected contemporaneously at three standing and two toppled oil and gas platforms located ∼130 km off the coast of Louisiana. Stereo-video and GoPro® cameras were used to profile the water column to estimate the number, length, and species composition of fishes present on the platforms. Hydroacoustics were used to determine the spatial distribution, both in distance and depth, of relative fish biomass, or mean volume backscatter, within 500 m of the center of each site. Mean volume backscatter (MVBS, SV) was highest near the structure, then declined rapidly with distance. We estimated that background-noise level was obtained at ∼100 m from the structures. Fish MVBS was highest in the lower water column (>60 m depth), compared to 0–30 m and 30–60 m depth zones. Fish communities differed among depth layers, seasonally, and between structure types (standing/toppled), though red snapper (Lutjanus campechanus) was the dominant species present at both structure types. Coupled video sampling revealed that MVBS changed little seasonally, but different species contributed to community structure seasonally and among layers in the water column. This study is one of several studies to use video data combined with acoustics to describe species contribution to acoustic biomass at standing and toppled platforms. We contend that integrating these non-destructive sampling methods is an important step in understanding the efficacy of artificial structures as ecological valuable habitat.