Seasonal and Spatial Variation in the Biomass and Size Frequency Distribution of the Fish Associated with Oil and Gas Platforms in the Northern Gulf of Mexico
Stanley, David R. and Charles A. Wilson
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The largest artificial reef complex in the world, although unplanned, is composed of the 4,000 petroleum platforms scattered across the outer continental shelf (OCS) of the northern Gulf of Mexico (GOM). Scientists have hypothesized that artificial reefs and platforms improve and/or diversify habitat, increase resources, modify the assemblages of organisms in the region or concentrate existing resources. The placement of these defacto reefs has undoubtedly impacted the regional marine community although little information is available. Only recently have assessment methods been developed to test these and other hypotheses concerning artificial reefs....With the sampling protocol established, the objectives of this research were to use dual beam hydro acoustics in conjunction with visual point count surveys to measure the density and size distribution of fishes associated with three petroleum platforms off the Louisiana coast. The goals of this research were to determine the effect of water depth on fish density, size distribution and species composition and ultimately to measure the fisheries value of platforms of different depths in the same geographical region. The results of this project demonstrate the variability in abundance, size distribution and species composition of fishes associated with petroleum platforms. Similar results from earlier studies have been found with natural and artificial reefs. The variability in density and the size distribution of fishes at petroleum platforms in this project was linked to temporal, spatial and environmental variables.... This research confirms the variability of fish assemblages associated with petroleum platforms and reinforces the need to sample on each side and throughout the water column to obtain an accurate estimate of fish abundance. The high abundance of fishes found at the sites demonstrates the importance of petroleum platforms to the marine environment of the northern GOM. Although some variance was observed, 10,000 to 30,000 fishes were found per site at any one time and since over 1,000 platforms are located in similar water depths it is clear that these structures impact the fisheries of the region. This study continues to demonstrate the utility of margining hydro acoustics and visual survey techniques to study the assemblage of fishes associated with petroleum platforms. The combination of these techniques allows for the measurement of the area of influence of these defacto artificial reefs, as well as estimates of abundance, size distribution and species composition throughout the water column and over long time periods.