Abundance, Distribution, and Habitat Use of Sharks in Two Northeast Florida Estuaries

• Main Author: McCallister, Michael Philip
• Format: Thesis
• Language: unknown
• Published: UNF Digital Commons 2012
• Subjects: University of North Florida; UNF; Dissertations; Academic – UNF – Master of Science in Biology; Academic – UNF – Biology; Thesis; Carcharhiniformes; Atlantic sharpnose shark; Blacktip shark; Hammerhead sharks; Sandbar shark; Estuarine fishes; Estuarine health; Estuarine ecology > Cumberland Sound (Ga. and Fla.); Estuarine ecology > Florida > Nassau River; Biology; Cumberland Sound
• Online Access: https://digitalcommons.unf.edu/etd/352; https://digitalcommons.unf.edu/cgi/viewcontent.cgi?article=1405&context=etd

Sharks are considered top predators in many marine ecosystems, and can play an important role in structuring those communities. As a result, it is necessary to understand the factors that influence their abundance and distribution. This is particularly important as fishery managers develop fishery management plans for sharks that identify areas that serve as essential fish habitat (EFH). This includes nursery habitat where sharks are born and juveniles spend the early part of their life. However, our understanding of shark habitat use in the northeast Florida waters is limited. The goal of this thesis was to characterize the abundance and distribution of sharks in northeast Florida estuaries, and to examine the effect of abiotic and biotic factors affecting shark habitat use. A bottom longline survey conducted from 2009 – 2011 indicated that 11 shark species use the estuarine waters of northeast Florida during summer months. Atlantic sharpnose (Rhizoprionodon terraenovae), blacktip (Carcharhinus limbatus), bonnethead (Sphyrna tiburo), and sandbar sharks (Carcharhinus plumbeus) were the most abundant species and made up 87.1% of the total catch. Month, bottom water temperature, and depth were the most important factors determining the presence and abundance of these species. This study also examined the role of prey abundance in determining the abundance of Atlantic sharpnose sharks. The probability of catching an Atlantic sharpnose shark, and the abundance of Atlantic sharpnose sharks, were most influenced by site. Neither potential prey abundance nor preferred prey abundance were not significant factors effecting Atlantic sharpnose abundance. This may be a result of prey sampling not providing an accurate measure of the true availability of prey resources. Other factors, such as predation risk, may better explain habitat use patterns of Atlantic sharpnose sharks. Continued sampling will give a better understanding of the factors influencing shark habitat use in this area.