Juvenile Density, Fishing Mortality, and Habitat use of Red Snapper, Lutjanus campechanus, on Artificial and Natural Reefs in the Northern Gulf of Mexico.
Type of DegreePhD Dissertation
Fisheries and Allied Aquacultures
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The Red Snapper, Lutjanus campechanus, fishery in the Gulf of Mexico has been intensively regulated as managers attempt to rebuild the fishery. This has led to a need for improved data collection, and a better understanding of Red Snapper biology. This study examined three aspects of the biology and fishery of Red Snapper. First, patch-reefs were examined as a novel method for estimating Red Snapper juvenile density as an index of year-class strength, which could improve fishery management efforts if years of strong or weak year classes can be measured before they enter the directed fishery. The timeframe examined also included years before and after the 2010 Deepwater Horizon oil spill, allowing for an evaluation of the spill’s effects on juvenile Red Snapper. Second, the present study estimated tagging mortality, natural mortality and fisher nonreporting from acoustic telemetry of Red Snapper to calibrate a conventional mark-recapture study to improve fishing mortality estimates, which can increase the accuracy of management efforts. Finally, while many artificial reefs have been deployed in the northern Gulf of Mexico to improve fishing opportunities, it is unclear if these artificial reefs function differently than natural reefs. Fine scale telemetry methods were used to compare Red Snapper home range, diel and seasonal behaviors, site fidelity, and mortality on natural reefs and artificial reefs to help improve our understanding of how Red Snapper use these different habitats. High densities of age-0 Red Snapper in 2009, 2011, and 2013 on patch-reefs indicated years of higher potential year classes of Red Snapper. The density of age-0 Red Snapper in 2010 was low at an offshore location, but similarly low densities were also observed in other years. The density of age-0 Red Snapper in 2010 at an inshore location, and the density of age-1 Red Snapper in June 2011 were similar to other years. Thus, the present study detected little effect of the 2010 Deepwater Horizon oil spill on the density of age-0 Red Snapper on patch-reefs. Mean fishing mortality for Red Snapper greater than 406 mm total length was F = 0.22 in 2015 and 2016, with an estimated annual harvest of 212,237 fish per year. These results were based on estimates of tagging mortality, natural mortality, tag shedding, and fisher nonreporting from telemetry that were applied to the conventional tagging effort, and accounting for Red Snapper distributions on different reef types. Red Snapper living on both natural and artificial reefs had similar mortality rates, site fidelity and movement patterns, and similar relations to changing seasons and temperature on these two reef types. These observed similarities indicated that these two reef types have similar ecological functions for Red Snapper. Importantly, fishing mortality rates were nearly identical on both reef types and provided little evidence that artificial reefs disproportionally concentrate Red Snapper and increase exploitation compared to natural reefs. Red Snapper are closely tied to reef structure, even at the youngest ages. The present study used this association to measure year-class strength, and to estimate fishing mortality in this valuable fishery. Importantly, this study indicated little difference in Red Snapper behavior and exploitation between natural and artificial reefs. This supports the idea that artificial reefs benefit, rather than harm, Red Snapper populations. Thus, further artificial reef deployments have the potential to increase Red Snapper habitat, even at early life stages.