An Analysis of Artificial Reef Fish Community Structure along the Northwestern Gulf of Mexico Shelf: Potential Impacts of “Rigs-to-Reefs” Programs

Artificial structures are the dominant complex marine habitat type along the northwestern Gulf of Mexico (GOM) shelf. These habitats can consist of a variety of materials, but in this region are primarily comprised of active and reefed oil and gas platforms. Despite being established for several decades, the fish communities inhabiting these structures remain poorly investigated. Between 2012 and 2013 we assessed fish communities at 15 sites using remotely operated vehicles (ROVs). Fish assemblages were quantified from standing platforms and an array of artificial reef types (Liberty Ships and partially removed or toppled platforms) distributed over the Texas continental shelf. The depth gradient covered by the surveys (30-84 m) and variability in structure density and relief also permitted analyses of the effects of these characteristics on fish richness, diversity, and assemblage composition. ROVs captured a variety of species inhabiting these reefs from large transient piscivores to small herbivorous reef fishes. While structure type and relief were shown to influence species richness and community structure, major trends in species composition were largely explained by the bottom depth where these structures occurred. We observed a shift in fish communities and relatively high diversity at approximately 60 m bottom depth, confirming trends observed in previous studies of standing platforms. This depth was also correlated with some of the largest Red Snapper captured on supplementary vertical longline surveys. Our work indicates that managers of artificial reefing programs (e.g., Rigs-to-Reefs) in the GOM should carefully consider the ambient environmental conditions when designing reef sites. For the Texas continental shelf, reefing materials at a 50-60 m bottom depth can serve a dual purpose of enhancing diving experiences and providing the best potential habitat for relatively large Red Snapper

Impacts of Deep Oil Spills on Fish and Fisheries

The Gulf of Mexico (GoM) total fishery production varies around one million metric tons per year. Fishery production is based on a diverse set of invertebrate and finfish species, including estuarine, continental shelf, and open-ocean species. The GoM has been subjected to two large oil spills in the Southern (Ixtoc 1, 1979–1980) and in the Northern GoM (Deepwater Horizon 2010) that caused serious concern about impacts on the abundance and seafood safety of fishery resources. Scientific evidence does not indicate a collapse or a clear impact on long-term fishery productivity related to either the Ixtoc 1 or DWH oil spills. Fishery landings in the Northern GoM returned quickly to pre-spill levels, and short-term declines could be attributed to the extensive fishery closure in the US exclusive economic zone. In the Southern GoM, fishery production post-Ixtoc 1 decreased dramatically over time attributed primarily to overharvesting of the main target species. Although no oil spill impact on the fishery resources was apparent at the population level, there is considerable evidence of impacts at the organismal and sub-individual levels, and there is concern how these effects could impact fishery resources in the long term. The responses of fish and shellfish populations are analyzed in relation to reproductive strategies, distribution of nursery grounds and critical habitats, exploitation status, oil spill distribution, and overall pollution levels. Fish and shellfish populations show a high capacity to withstand/recover from natural and anthropogenic impacts by taking advantage of favorable environmental conditions and by evolving life history strategies robust to seasonal and interannual variability. Stock resiliency is affected by several factors but mainly overharvesting that may reduce reproductive potential and compromise fishery resource resiliency in the eventual case of another large-scale oil spill disaster