Investigating Georgia's shark nurseries
Belcher, Carolyn Niles
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Many shark species along the Atlantic coast of the United States have been fished to unsustainable population levels over the past 30 years. There is a direct relationship between the numbers of adults and young in a population for most shark species, but data about the immature portion of stock is scarce. Neonate and small juvenile sharks use near shore waters and inshore embayments as nursery areas where they are protected from predators and prey are abundant. However, neonate sharks are susceptible to human influences on habitat as well as increased rates of fishing mortality associated with recreational and commercial fisheries. In this dissertation, I present the results of work that examined: 1) potential sources of bias that could affect longline estimates of abundance estimates for common shark species; 2) the utility of a fishery-independent trawl survey for assessing the distribution and abundance of sub-adult sharks; 3) the relative importance of mesohabitat characteristics in defining habitat use for common species; and 4) the effects of the shrimp trawl fishery on sub-adult sharks. My findings demonstrate that bait type can bias longline catch rates and species selection. My examination of gear efficacy revealed that although longline and trawl surveys provide similar information, the trawl provides the distinct advantage of being able to sample offshore waters and currently is the only gear that captures neonate bonnethead sharks. Results from the mesohabitat evaluation indicate that bonnethead and sandbar sharks do have unique water chemistry preferences; however, mesohabitat characteristics better explain the absence of these species from sampling areas. Finally, my investigation of the effects of commercial shrimp trawls reveal that although sub-adult sharks are captured in trawls, the current management regime for this fishery may be already be sufficiently conservative to offer moderate protection from fishing mortality. Sub-adult sharks in Georgia’s estuaries are apex predators that play a critical part in maintaining the health of the ecosystem. Protecting shark nursery areas is one mechanism to rebuild the severely depleted stocks of sharks and a means to ensure the continued health of Georgia’s coastal ecosystems.