Abundance and Distribution of Sharks in Northeast Florida Waters and Identification of Potential Nursery Habitat

Michael Mccallister,Ryan Ford,James Gelsleichter

doi:10.1080/19425120.2013.786002

Abstract

AbstractSharks are considered top predators in many marine ecosystems and can play an important role in structuring community ecology. As a result, it is necessary to understand the factors that influence their abundance and distribution. This is particularly important as fishery managers develop management plans for sharks that identify areas that serve as essential fish habitat, especially nursery habitat. However, our understanding of shark habitat use in northeast Florida waters is limited. The goal of this study was to characterize the abundance and distribution of sharks in northeast Florida estuaries and to examine the effect of abiotic factors on shark habitat use. A bottom longline survey conducted from 2009 to 2011 indicated that 11 shark species use the estuarine waters of northeast Florida during the summer months. Atlantic Sharpnose Sharks Rhizoprionodon terraenovae, Blacktip Sharks Carcharhinus limbatus, and Bonnetheads Sphyrna tiburo were the most abundant species and made up 81.4% of the total catch. Site, month, and bottom water temperature were the most important factors determining the presence and abundance of sharks and suggest both regional and seasonal variations in the use of northeast Florida waters. Depth, salinity, and dissolved oxygen were also important factors. Our data show that these waters serve as a nursery for Atlantic Sharpnose and Blacktip Sharks, with young‐of‐the‐year and juveniles being present in the summer months. Limited tag–return data reveal that juvenile sharks remain in these waters throughout the summer and that some return in subsequent summers. This is the first study to characterize the abundance and distribution of sharks and identify potential nursery areas in northeast Florida estuaries.Received October 10, 2012; accepted March 7, 2013

Highlights

Sharks are considered top predators in many marine ecosystems and can play an important role in structuring community ecology
More recently, the shark nursery concept was reexamined by Heupel et al (2007), who proposed a definition with three criteria that could be used to quantitatively identify shark nursery habitat: (1) juvenile sharks are more commonly encountered in these areas than in others, (2) juvenile sharks will remain or return to these areas over an extended period of time, and (3) the areas will be utilized repeatedly across years
Eleven species were caught from 2009 to 2011, including species in both the small and large coastal shark management units. This suggests that the estuarine waters of Cumberland and Nassau sounds support a wide variety of shark species

Summary

Introduction

Sharks are considered top predators in many marine ecosystems and can play an important role in structuring community ecology. It is necessary to understand the factors that influence their abundance and distribution This is important as fishery managers develop management plans for sharks that identify areas that serve as essential fish habitat, especially nursery habitat. Limited tag–return data reveal that juvenile sharks remain in these waters throughout the summer and that some return in subsequent summers This is the first study to characterize the abundance and distribution of sharks and identify potential nursery areas in northeast Florida estuaries. Of particular importance in their role as EFH are nearshore estuarine and marine ecosystems (e.g., seagrass meadows, marshes, and mangroves) that serve as nursery habitats, providing a selective advantage for juveniles This may include increased prey abundance and decreased risk of predation (Branstetter 1990; Castro 1993), both of which would have obvious benefits for survival and overall population growth. There have been no studies examining the presence of shark nursery habitat in northeast Florida

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