Andros, Bahamas – Great hammerhead sharks, renowned for their impressive long-distance migrations across oceans, seemingly have a stay-at-home contingent in the Bahamas. Scientists are now exploring a surprising reason why some of these critically endangered giants embark on epic journeys while others happily remain in the protected, food-rich waters of this island nation: their taste for different prey.
New research published in Frontiers in Marine Science suggests that individual dietary preferences could be a key factor driving the migratory behavior of great hammerheads ( Sphyrna mokarran). While some individuals undertake documented journeys of up to 3,000 kilometers between Bimini, Bahamas, and the coast of Virginia, others appear content to reside year-round in the Bahamian shark sanctuary established in 2011.
“Resource availability is definitely a major factor,” explains shark ecologist Tristan Guttridge, founder of the marine nonprofit Saving the Blue, who led the research in Andros. “The Bahamas offer abundant food. But the question was, if there’s plenty to eat here, why do some hammerheads still feel the urge to leave?”
The answer, Guttridge and his team propose, might be as simple as culinary cravings. Just as a person might travel across town for a specific dish despite having numerous food options nearby, hammerheads may migrate to find their preferred meals.
Between 2018 and 2024, researchers observed and tracked 78 hammerheads in Andros. They collected detailed measurements and tissue samples from 22 sharks, and equipped seven with satellite tags to monitor their movements. As expected, some tagged sharks ventured far beyond the Bahamas, mirroring typical migratory patterns for the species. However, a significant portion opted to stay within the Andros region throughout the year.
Analyzing the isotopic signatures within the sharks’ tissue – a method that reveals the origin of atoms and thus, dietary sources – the team discovered striking differences in individual diets. Astonishingly, one hammerhead appeared to have a strong preference for silky sharks, with this prey species making up nearly two-thirds of its diet. Others primarily consumed barracuda and stingrays.
This dietary divergence, researchers believe, could be directly linked to migration. Silky sharks are predominantly found in open ocean environments, while stingrays are typically bottom dwellers, and barracuda inhabit both coastal and open waters. “We uncovered clear evidence of individual variation in their diets,” Guttridge states. “This suggests that the decision to migrate or stay put might fundamentally depend on what a particular shark prefers to hunt and eat.”
Understanding these dietary nuances carries significant conservation implications for great hammerheads. These magnificent creatures are classified as critically endangered, with global populations estimated to have plummeted by over 80% in the last three generations. Their extensive migrations expose them to perilous encounters with industrial fishing operations in international waters, where they are vulnerable to being caught as bycatch or targeted for their fins.
“While the Bahamas shark sanctuary provides crucial year-round protection for some individuals, it’s clear that not all hammerheads benefit equally,” Guttridge emphasizes. “This research highlights the urgent need for international collaboration in conservation efforts. To effectively protect these highly mobile and endangered animals, we must understand their unique needs and their movements, which are increasingly linked to their individual tastes and dietary choices.” By recognizing that a taste for silky shark versus stingray might be a key to understanding hammerhead behavior, scientists are gaining valuable insights to inform more targeted and effective conservation strategies for these ocean giants.
