Investigating Tiger Shark Movement at Tiger Beach, Bahamas

Investigating Tiger Shark Movement at Tiger Beach

Project Overview

The tiger shark is the largest predatory fish in tropical seas. At Tiger Beach, a popular dive site in the Bahamas, boats lure tiger sharks within close proximity of SCUBA divers so that the dive tourists can see the sharks up-close. The overall goal of this project is to evaluate the behavioral ecology of tiger sharks at Tiger Beach and specifically to determine:

  • Overall residency patterns of sharks within and outside of the Bahamas Shark Sanctuary
  • Movement patterns within and in and out of Tiger Beach
  • Effect of dive tourism on tiger shark behavior and movements
  • Use of Tiger Beach as a mating ground, feeding area, or gestation ground
  • Vulnerability of sharks to fishing exploitation outside of the Bahamas Shark Sanctuary
  • Body condition and health impacts on shark movement patterns 

To address these questions, this study combines acoustic telemetry, satellite tagging, blood-hormone analysis, and ultrasonography to analyze tiger sharks. To implement these methods, tiger sharks are carefully caught using a specialized fishing system and either secured to the side of the boat or placed onto a partially submerged platform where they can be quickly measured, a blood sample taken, tagged, and released. Historically, the reproductive biology of sharks has been studied by sacrificing the animals; however, in this study, in-water ultrasounds are performed while the shark is secured. The blood samples are taken for hormone analysis to determine reproductive status. Coupling these techniques (ultrasonography imaging and blood hormone analysis) allows researchers to determine the reproductive state (e.g., is a female tiger shark pregnant) and length of gestation.

Two types of tags are used to monitor the tiger sharks. To examine the large-scale movement patterns, satellite tags are affixed to their dorsal fins. To examine the fine scale residency patterns at Tiger Beach, acoustic tags are implanted in the abdomen of the sharks. The transmitters within the acoustic tag sends off an ultrasonic signal that is picked up by a series of hydrophones strategically positioned throughout Tiger Beach. These hydrophones record the date and time when an acoustically tagged tiger shark swims within about 500 m of a hydrophone.

Why this matters

Tiger Beach is within the boundaries of the Bahamas Exclusive Economic Zone, where sharks are protected from all harvest due to the establishment of a Shark Sanctuary in 2011. If females spend their entire pregnancy and potentially give birth within Bahamian waters, then the sanctuary would indeed serve as an effective conservation tool for this species. However, if pregnant females spend little time within the sanctuary due to tourism pressure, and/or give birth outside the sanctuary, they may be vulnerable to exploitation when they move out, reducing the efficacy of the protected area.

Lead Organizations

Partners

  • Austin Gallagher, Beneath the Waves Inc.
  • Steve Cooke, Carleton University
  • Mike Heithaus, Florida International University
  • James Sulikowski, Arizona State University

Supported by

Project Status

  • Overall study is ongoing; acoustic telemetry portion has been completed and receivers removed from Tiger Beach

Contact

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