Use of Human‐Altered Habitats by Bull Sharks in a Florida Nursery Area

Tobey H Curtis,Daryl C Parkyn,George H Burgess

doi:10.1080/19425120.2012.756438

Abstract

AbstractBull Sharks Carcharhinus leucas in the Indian River Lagoon, Florida, have been documented to frequently occur in human‐altered habitats, including dredged creeks and channels, boat marinas, and power plant outfalls. The purpose of this study was to examine the short‐term movements of age‐0 and juvenile Bull Sharks to quantify the extent to which those movements occur in altered habitats. A total of 16 short‐term active acoustic tracks (2–26 h) were carried out with 9 individuals, and a 10th individual was fitted with a long‐term coded transmitter for passive monitoring by fixed listening stations. Movement and activity space statistics indicated high levels of area reuse over the span of tracking (hours to days). All but one shark usedaltered habitat at some point during tracking, such that 51% of all tracking positions occurred in some type of altered habitat. Of the sharks that used altered habitat, the mean (±1 SD) percent of positions within altered habitat was 66 (±40)%. Furthermore, tracks for 3 individuals indicated selection for altered habitats. The single passively monitored Bull Shark was detected in power plant outfalls almost daily over a 5‐month period, providing the first indication of longer‐term fidelity to thermal effluents. Use of one dredged creek was influenced by local salinity, the tracked sharks dispersing from the altered habitat when salinity declined. The affinity of young Bull Sharks to altered habitats in this system could help explain their reported accumulation of a variety of harmful contaminants, which could negatively affect their health and survival.Received July 27, 2012; accepted November 28, 2012

Highlights

Florida, have been documented to frequently occur in humanaltered habitats, including dredged creeks and channels, boat marinas, and power plant outfalls
Short-term active tracking and preliminary long-term passive tracking both indicate that (1) Bull Sharks in this system typically show restricted movements, and (2) those movements are frequently tied to habitats that have been altered and degraded by human activity, including dredged estuarine creeks, marinas, dredged channels, and power plant outfalls
Downloaded From: https://bioone.org/journals/Marine-and-Coastal-Fisheries:-Dynamics,Management,and-Ecosystem-Science on 02 Nov 2021 Terms of Use: https://bioone.org/terms-of-use has been observed in other active tracking studies of Bull Sharks (Steiner and Michel 2007; Ortega et al 2009), but these studies occurred in comparatively less developed regions

Summary

Introduction

Florida, have been documented to frequently occur in humanaltered habitats, including dredged creeks and channels, boat marinas, and power plant outfalls. This niche expansion into freshwater environments is hypothesized to benefit Bull Sharks by providing nursery habitat with high prey availability and refuge from predation by larger sharks or by otherwise allowing Bull Sharks to exploit resources not accessible to shark species intolerant of low salinity (Branstetter 1990; Pillans and Franklin 2004; Heupel and Simpfendorfer 2011) This inshore distribution could make neonate and juvenile Bull Sharks disproportionately vulnerable to the effects of estuarine habitat degradation (Curtis et al 2011). Knowledge of these movement patterns is essential to acquiring a better understanding of the use by Bull Sharks of potentially harmful habitats

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