HCAS Research on Hammerhead Shark Migrations Identifies their Seasonally Resident Areas
Hammerhead sharks are some of the most iconic and unique-looking creatures in our oceans. While some may think they look a bit “odd,” one thing researchers agree on is that little is known about them. Many of the 10 hammerhead shark species are severely overfished worldwide for their fins and in need of urgent protection to prevent their extinction.
To learn more about a declining hammerhead species that is data poor but in need of conservation efforts, a team of researchers from NSU’s Save Our Seas Foundation Shark Research Center (SOSF SRC) and Guy Harvey Research Institute (GHRI), Fish Finder Adventures, the University of Rhode Island and University of Oxford (UK), embarked on a study to determine their migration patterns in the western Atlantic Ocean.
The research team satellite tagged sharks off the US Mid-Atlantic coast and then tracked the sharks for up to 15 months. The sharks were fitted with fin-mounted satellite tags that reported the sharks’ movements in near real time via a satellite link to the researchers.
“Getting long-term, high resolution tracks was instrumental in identifying not only clear seasonal travel patterns but also the times and areas where the sharks were resident in between their migrations – key information for management action to help build back this depleted species,” said Ryan Logan, a Ph.D., student at the Halmos College of Arts & Sciences and Guy Harney Oceanographic Research Center (HCAS), GHRI and SOSF SRC, and first author of the newly published research.
The researchers found that the sharks acted like snowbirds, migrating between two seasonally resident areas – in coastal waters off New York in the summer and off North Carolina in the winter.
“The high resolution movements data showed these focused wintering and summering habitats off North Carolina and New York, respectively, to be prime ocean “real estate” for these sharks and therefore important areas to protect for the survival of these near endangered animals,” said Mahmood Shivji, Ph.D., professor in the HCAS and director of the GHRI and SOSF SRC, who oversaw the study.
Identifying such areas of high residency provides targets for designation as “Essential Fish Habitat” – an official title established by the US Government, which if formally adopted can subsequently be subject to special limitations on fishing or development to protect such declining species. The tracking data also revealed a second target for conservation. The hammerheads spent a lot of resident time in the winter in a management zone known as the Mid-Atlantic Shark Area (MASA) – a zone already federally closed for seven-months per year (January 1 to July 31) to commercial bottom longline fishing to protect another endangered species, the dusky shark. However, the tracking data showed that the smooth hammerheads arrived in the MASA earlier in December, while this zone is still open to fishing.
“Extending the closure of the MASA zone by just one month, starting on December 1 each year, could reduce the fishing mortality of juvenile smooth hammerheads even more”, said Shivji.
The tracks of the smooth hammerheads (and other shark species) can be found at