New Research Uncovers Residency Patterns of Great Hammerhead Sharks
A groundbreaking study has revealed that some great hammerhead sharks (Sphyrna mokarran) prefer to stay in one place rather than migrate. Researchers studying these apex predators around Andros Island, located within the Bahamas Shark Sanctuary, found that while some individuals undertake long migrations, others remain in a single area—likely due to the availability of ample resources. These findings could play a vital role in the conservation of this critically endangered species.
Declining Populations and Conservation Significance
“The global population of great hammerheads has declined by more than 80% over the past three generations,” said Dr. Tristan Guttridge of Saving the Blue, lead author of the study published in Frontiers in Marine Science. “Genomic studies indicate low genetic diversity and significant inbreeding, making conservation efforts even more crucial.”
Understanding movement patterns is key to protecting these sharks. The study highlights that some great hammerheads exhibit year-round residency in the Bahamas, providing them protection from fishing pressures within the sanctuary.
Tracking the Movement of Great Hammerheads
Great hammerheads are known to travel distances of up to 3,000 km. However, they also favor specific regions, such as Bimini, where they overwinter before leaving in the summer. The potential role of other Bahamian islands, such as Andros, in supporting these sharks remains less understood.
To bridge this knowledge gap, researchers focused on Andros Island, the largest in the Bahamas, known for its pristine reef systems and expansive flats habitat. “There was minimal data on great hammerheads in the central Bahamas, and no information on their habitat use in Andros,” explained Guttridge. “We didn’t even know what they primarily ate.”
Using a combination of electronic tagging and observational data collected between 2018 and 2024, the research team studied 22 sharks, attaching satellite trackers to seven individuals. By integrating this data with 78 recorded sightings, the researchers identified key behavioral trends.
Andros Island: A Prime Habitat for Great Hammerheads
Findings revealed that great hammerheads prefer specific regions off the eastern coast of north and central Andros. They showed long-term site fidelity, especially within a 400 km² zone rich in prey species. Some sharks returned to the same locations over several years, reinforcing the idea of site loyalty.
Sharks that ventured beyond the southern or northern tip of the island were more likely to migrate. Those that left Bahamian waters primarily traveled toward the U.S. East Coast, suggesting they are part of the broader western Atlantic population.
The study also found evidence of recent mating activity in the area, indicating its potential significance for reproduction. Half of all recorded sightings occurred between January and March, though a notable number were also spotted in June and July.
What’s on the Menu? Insights from Isotope Analysis
To better understand feeding habits, scientists conducted isotope analysis of muscle biopsies. Results showed that barracudas and stingrays accounted for about two-thirds of the sharks’ diets, with smaller sharks comprising the rest. However, individual dietary preferences varied—one shark’s diet was nearly 66% silky sharks.
This availability of prey, coupled with deep, cooler waters, may enable certain hammerheads to remain in the Bahamas year-round. However, not all sharks opt to stay, raising questions about the factors driving migratory behavior.
“Food abundance is a major factor in habitat selection, but individual dietary preferences may influence whether a shark stays or migrates,” said Guttridge. “There could also be a genetic component to migration, similar to what we see in species like salmon.”
The Future of Great Hammerhead Conservation
This study underscores the significance of Bahamian waters as a critical refuge for great hammerheads. While some individuals benefit from year-round protection, others travel beyond these safe zones, highlighting the necessity of international cooperation for their conservation.
“Our research emphasizes the need for expanded conservation efforts,” Guttridge concluded. “A key next step is understanding how these sharks fit within the broader Northwest Atlantic population and ensuring protective measures extend beyond the Bahamas.”
Reference:
Stay or go? Space and resource use of the great hammerhead (Sphyrna mokarran) off Andros Island, The Bahamas, Frontiers in Marine Science (2025). DOI: 10.3389/fmars.2025.1544482