OTN-supported shark tracking in the Bahamas and Florida

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Dr. Neil Hammerschlag is an OTN international project lead and marine ecologist based at the University of Miami Rosenstiel School of Marine and Atmospheric Science. His research focuses on the behaviour, conservation and movement of sharks. Hammerschlag’s shark-tracking work is conducted through OTN’s global acoustic tracking infrastructure—bottom-moored tracking stations in the Bahamas and off the coast of Miami, Florida. Small, implantable acoustic tags carried by the sharks emit a unique ID code (“ping”) picked up by the bottom-moored acoustic receivers. Data from the tags allow researchers to understand where sharks move and how they use their environment.

A tiger shark passes one of OTN’s bottom-moored acoustic receivers. These devices detect unique ID codes emitted from tags carried by marine life (photo: Jim Abernethy)

Tiger shark behaviours in the Bahamas — night & day

The Bahamas is a group of more than 700 islands stretching southwest, 300 kilometres east of Florida. Within the northwest edge of Little Bahama Bank, an area nicknamed “Tiger Beach” attracts sharks (and shark enthusiasts) in great numbers due to the shallow, warmer waters. Hammerschlag’s team uses this area to conduct research on sharks’ movements and behaviour.

A map of the acoustic tracking array/study area in the northern Bahamas. Hammerschlag et al. (2017, JEMBE)

The project uses an array of acoustic receivers in Little Bahama Bank—32 units over 102 square-kilometres, of which OTN provided 20. The research team collected tracking data from June 2014 to May 2015 from 42 acoustically tagged tiger sharks at Tiger Beach and the surrounding area. Surprisingly, within the Tiger Beach dive sites and the surrounding area, tiger shark movements were similar by day and night. Tiger sharks were shown to swim the entire area of the acoustic array, with activity spaces in the array averaging more than six kilometres during both day and night, with little spatial differences in habitat use. Most of the tagged sharks also left the array during summer months. Interestingly, the movements of tagged tiger sharks did not show any obvious signs of habituation to the dive sites, a phenomenon common in other parts of the world where sharks are lured by tour operators.

Two tiger sharks glide along the ocean floor.

“Our team has really been amazed by what this acoustic tracking technology has allowed us to learn about these animals,” said project leader, Neil Hammerschlag. “One of the coolest aspects is seeing where else the sharks go by collaborating with other research groups using acoustic receivers in the region.”

Hammerschlag’s research tracking tiger sharks was published in the Journal of Experimental Marine Biology and Ecology in June. You can learn more about this project here.

Acoustically tracking “urban” sharks in Miami & Biscayne Bay, Florida

A map of the acoustic array in Miami.

With the expansion of human settlements, many animals are appearing in urban centres. Though some species have flourished as scavengers in these environments, for others, man-made habitat may not be an ideal survival strategy.

As more people continue moving to coastal urban centres, the oceans become more heavily impacted by habitat alteration, boat traffic, fishing as well as noise and chemical pollution. The effects of this urbanization on marine and coastal species, especially predators, remains poorly understood. To address this knowledge gap, Hammerschlag and his team are investigating the effects of coastal urbanization on the health and behaviours of sharks off of Miami and Biscayne Bay in Florida.

As part of the study, Hammerschlag and the research team are using 32 acoustic receivers, 20 provided by OTN, dispersed from the skyscraper-laden shorelines of Miami’s highly urbanized downtown to the relatively pristine mangrove lined shorelines of Biscayne National Park. Bull sharks, nurse sharks, blacktip sharks and great hammerhead sharks are being tracked as part of this study.

A tagged nurse shark being released by the research team in downtown Miami. (Robbie Roemer, University of Miami Shark Research & Conservation Program)

The project was funded by a Key Stone Grant from the Save Our Seas Foundation, with additional support from the Disney Conservation Fund and through collaboration with the National Oceanic and Atmospheric Association.

Hammerschlag and his team capture and tag sharks in the urbanized waterways. The team, which includes long-term collaborator Dr. Austin Gallagher and graduate student Robbie Roemer, will compare this data to that of the sharks occupying more untouched areas. This study is ongoing with plans to analyze tracking data early next year.

Graduate student, Robbie Roemer performs surgery on a blacktip shark to insert an acoustic tag.

For more information on urban shark tracking in Miami, visit Save Our Sea’s website, or check out Shark Research and Conservation Program at the University of Miami’s project page.

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