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

Effects of a New Artificial Reef Complex on Red Snapper and the Associated Fish Community: an Evaluation Using a Before–After Control–Impact Approach

Artificial reefs are commonly created with the goal of enhancing fish populations. However, many studies evaluating their effects on these populations have been hindered by a lack of preconstruction data from existing natural habitats and temporal comparisons with control areas. Here, we present findings from a before–after control–impact study designed to assess the effects of a new artificial reef on fish populations in the western Gulf of Mexico. Vertical line and fish traps were used to sample the reef site and a paired control site with soft bottom substrates for 1 year before and 2 years after reef construction. Prior to reef construction in October 2013, and over bare substrates in general, infrequent catches of sea catfishes and small coastal sharks were observed. With the exception of rare occurrences of juvenile Gray Triggerfish Balistes capriscus and Red Snapper Lutjanus campechanus, which were observed only during the summer recruitment season, the control site exhibited a lack of reef species. In contrast, we documented dramatic increases in the frequency of occurrence and abundance of multiple reef species at the reef site following the addition of structured habitat. Distinct cohorts of Red Snapper could be followed through time suggesting site fidelity, and few fish greater than age 2 years were captured indicating limited migration of older fish from other areas. Given that the reef supported high densities of juvenile Red Snapper that were in good condition, growing quickly, and protected from potential shrimp trawl mortality, export of juveniles (i.e., production) to the adult population was evident and likely greater on a per-unit-area basis than for the control site. Our study highlights the potential benefits of artificial reefs to species like Red Snapper; however, future studies should investigate the relative roles of emigration and fishing mortality to better understand the effects of these structures on reef fish population dynamics

Reproductive characteristics of Red Snapper Lutjanus campechanus on artificial reefs in different jurisdictions

Reproductive activity of Red Snapper Lutjanus campechanus (Poey, 1860) at artificial reefs (ARs) are only recently being investigated. Yet, the management of the fishery differs on a regional basis with state and federal jurisdictions, and reproductive differences among regions have not been investigated. To compare the reproductive activity of L. campechanus among state (inshore) and federal (offshore) jurisdictions, individuals were collected in the northwestern Gulf of Mexico from four ARs on a quarterly basis for 2 yrs. Inshore sites exhibited fishing pressure year round whereas offshore sites only had fishing season open during a few months of summer. Collected individuals were measured for weight and length, then aged, sexed, and reproductive phase identified using the following metrics: resting, spawning capable, actively spawning, and regressing. Individuals in all reproductive phases were collected at three of the four sites. Spawning season was observed from April to September, with June identified as the induction of the peak spawning period. Hydrated oocytes were observed, which indicated imminent spawning within 12 h. Although 79% of female L. campechanus at all sites combined were mature based on reproductive phase, most fish were small, young, and inshore sites only made up 12% of the mature females. Several individuals were mature at offshore sites compared to only a few at inshore sites, yet fishing pressure was higher at inshore sites. We suggest that L. campechanus were spawning capable and actively spawning when those individuals were several years of age, but younger, barely mature individuals comprised the majority. Thus, L. campechanus include ARs in their life cycle and directly spawn on state and federal ARs when given enough time to achieve reproductive maturity. However, fisheries management should consider enforcing higher restrictions depending on the jurisdiction to allow individuals to mature and spawn before capture in both state and federal jurisdictions

Bubble scatter plot of Red Snapper Mean Total Length (TL) by bottom depth.

<p>Circle size is scaled to the number of individuals contributing to the mean. A second order polynomial (quadratic) curve is fit to the data to demonstrate a potential non-linear relationship with bottom depth.</p

Locations where various taxa were recorded on remotely operated vehicle surveys between 2012 and 2013.

<p>Locations where various taxa were recorded on remotely operated vehicle surveys between 2012 and 2013.</p

CLUSTER diagram showing linkages of assemblages by structure type and bottom depth.

<p>Linkages shown are based on Bray-Curtis similarity matrix. Values next to symbols represent bottom depths (meters).</p

Map of ROV Survey Sites.

<p>Artificial reef sites (red stars) and platforms (yellow circles) surveyed with ROVs between 2012 and 2013. Bathymetric countours are indicated by gray lines in 20 m increments. Inset map indicates location of survey sites relative to Gulf of Mexico.</p

Structural characteristics of artificial reefs and standing platforms surveyed between 2012 and 2013.

<p>Structural characteristics of artificial reefs and standing platforms surveyed between 2012 and 2013.</p

Results from BIO-ENV test examining the reef site characteristics best explaining fish assemblage composition.

<p>Results from BIO-ENV test examining the reef site characteristics best explaining fish assemblage composition.</p

Results from Analysis of Similarity pairwise comparisons.

<p>Results from Analysis of Similarity pairwise comparisons.</p