Ecology of red snapper in the western Gulf of Mexico: comparisons among artificial and natural habitats
Streich, Matthew Karl
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Artificial reef development is a popular management tool used to enhance fish stocks, mitigate degradation or loss of natural habitats, and provide additional recreational opportunities. Despite the popularity and support for artificial reef programs, our understanding of how artificial reefs affect marine fisheries is surprisingly limited. Thus, the goal of my study was to use concurrent comparisons of artificial reefs and natural habitats to provide key information to evaluate the utility of artificial reefs for reef fishes, in particular Red Snapper, in the western Gulf of Mexico (GOM). In Chapter 1, I used remotely operated vehicle surveys to show fish communities differ between artificial reefs and natural banks. While Red Snapper density was greater over artificial structures, estimates of total abundance and biomass were much greater on natural banks—approximately 7.6% of the 2012 GOM annual catch limit. In Chapter 2, I examined whether Red Snapper size structure and age and growth differ between artificial and natural habitats. Size and age distributions suggested natural banks supported more large and old individuals, and the logistic growth model suggested fish at artificial reefs reached larger sizes-at-age than those from other habitats. In Chapter 3, I assessed vertical line gear performance and demonstrated differences in gear efficiency between artificial reefs and natural banks. The use of paired video revealed a high prevalence of gear saturation, which should be accounted for if vertical lines are used in providing indices of abundance. In Chapter 4, I examined the effects of a newly created artificial reef using a before-after control-impact study. Following reef construction, juvenile Red Snapper abundance dramatically increased, and cohorts could be identified through time suggesting site fidelity. Because juvenile Red Snapper were present in high densities, appeared to be in good condition and growing quickly, and were no longer exposed to shrimp trawl mortality, the new reef likely enhanced the export of juveniles (i.e., production) to the adult population. Collectively, my findings suggest artificial reefs can be a valuable tool for enhancing the Red Snapper population. Given the large area of natural habitats in the GOM, artificial reefs may also be an effective management option for diverting fishing effort away from a large portion of the stock. Furthermore, fish at artificial habitats appear to grow as well as those on natural habitats, and artificial reefs can provide nursery habitat to juveniles. To increase the role artificial reefs play in supporting the GOM Red Snapper stock, future research should identify reef designs that maximize growth, survival, and production.