LB 25-214 - Utilization of offshore oil platforms by fish as artificial reefs in the Northern Gulf of Mexico

Large offshore structures, such as platforms for petroleum extraction and wind turbines, can function as artificial reefs andbecome habitats for many fish species. However, theirimportance for fish depends on location, surrounding environmental conditions, and other factors that characterize thestructures. Here, we analyze fish counts at oil platforms in the northern Gulf of Mexico to find their association with the environmental characteristics that exist at oil platforms. The data were collected with the combination of hydroacoustic and submersible rotating video surveys and consisted of counts of 38 species of fish at various depths at 70 oil platforms. We exploredhow two abundant species (Red snapper, Lutjanus campechanus; and Greater amberjack, Seriola dumerili) were associated with 62 explanatory variables at these sites. These variables included temperature, salinity, dissolved oxygen, distance from the shelf edge, bottom type, distance from the nearest port, depth of the structure, and distance from reefs orstructures. Because many of these variables are co-linear, random forest analysis was used. The dissimilarity of total fish species composition among sampling occasions was also investigated using a Bray-Curtis dissimilarity measure and ordination analysis (nonmetric multidimensional scaling analysis). The results from the analysis of the two species suggest their incidences are highly predictable (AUC of 0.923 for Red snapper and 0.926 for Greater amberjack based on the 20% test-data set). Red snapper incidence was explained mostlyby the distance to the shelf edge and temperature whereas Greater amberjack incidence was explained most by latitude. On the other hand, the counts of the two species were not predictable according to the pseudo R2 of the test data set. The results of total fish species composition suggest that one of the ordination axes was explained by temperature, which changes the most along vertical layers of sampling, and that the other ordination axis was explained by the distance to the shelf edge. Both results consistently suggest the relative location to the shelf edge is one of the important factors determining how oil platforms may function as artificial reefs. These findings contribute to the understanding of artificial reef ecology and can be used when attempting to find synergies between fisheries and offshore energy siting.