Ocean Community News

Migratory Connectivity of the Great Hammerhead Shark in the U.S. and Bahamas

The great hammerhead shark, Sphyrna mokarran, is one of the ocean’s most powerful predators. It is found in inshore and deep waters in tropical, subtropical and temperate regions.

Although small communities treasure the fins and consider dried, salted. and smoked hammerhead meat a delicacy, the sharks are not specific targets for large-scale commercial fishing. However, they are commonly caught as bycatch victims and have recently been categorized as “Endangered” on the Red List for the International Union for the Conservation of Nature (IUCN). According to IUCN, populations of the great hammerhead have declined by around 80 percent in the last 25 years.

Being able to locate key hot spots for these species for their migratory patterns is extremely useful for sustaining a healthy population. A team of scientists have become the first to provide evidence that these sharks are not the “ocean wanderers” experts have previously thought, but undergo long migratory journeys to return to specific areas. Their highly mobile activity suggests these sharks play an important part in ecosystem structure and stability in the ocean.

With the use of biotelemetry techniques such as tagging, laser photogrammetry and photo identification, Dr Tristan Guttridge and his team were able to measure the extent of migratory movements and site dependence for the sharks. The team focused on two sites: Bimini, a small chain of mangrove- fringed islands in the Bahamas; and Jupiter, Florida, a narrow continental drop-off point into the deeper waters of the Gulf Stream.

Scientists suggests that this study provides the first evidence for “philopatric behaviour to overwintering sites in the U.S and Bahamas in the highly mobile great hammerhead shark.”

At both sites, the team were able to capture and equip the sharks with acoustic, satellite and conventional tags. However, exceptionally clear water at Bimini enabled the team to free dive to attach tags, use laser photogrammetry, and photo identification. These photographs were taken to assess individual markings and morphology for each of the sharks for future tracking data.

Improvements in our understanding of the migratory movements of the Great Hammerhead have substantial implications for their management and allow marine planners to improve protection of the great hammerhead shark.

By: Alice Walsh, University of Portsmouth, School of Biological Sciences (Institute of Marine Sciences)

ecoCURRENTS is a joint initiative between ECO and select universities, which benefits science students by recruiting them to summarize the latest marine science research and providing them with a published byline. Currently, the University of Portsmouth, School of Biological Sciences (Institute of Marine Science) and Texas A&M-Corpus Christi participate in the project. Select articles also appear in ECO’s print edition.

ECO expects to add more universities to this initiative during 2017. Interested administrators should contact Greg Leatherman at This email address is being protected from spambots. You need JavaScript enabled to view it..

ECO Magazine is a marine science publication committed to bringing scientists and professionals the latest ground-breaking research, industry news, and job opportunities from around the world.


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