Hammerheads prefer a shark-eat-shark diet

While many sharks hunt for small, abundant prey when looking for a meal, great hammerheads have a supersized strategy with some big payoffs — eat other sharks.

For a long time, scientists have observed great hammerheads hunting other sharks, including blacktips during their seasonal migrations off Florida. But the energetic benefits of this high-risk, high-reward strategy were unclear until now.

New research published in the journal Oecologia reveals great hammerheads may gain significant energetic advantages by preying on large targets like large fish, rays and other sharks, according to lead author and FIU alumna Erin Spencer.

“In order to help protect critically endangered species like great hammerheads, we need to understand their underlying biology and how they interact with their environment,” Spencer said. “It’s important that we continue to study these big questions, especially in the face of a changing ocean.”

Spencer conducted the research alongside FIU’s Yannis Papastamatiou, one of the world’s leading shark behavioral ecologists, and a team of international researchers. They used advanced biologging technology to understand the foraging behaviors of great hammerhead sharks, known for their distinctive hammer-shaped heads and impressive size, sometimes reaching up to 20 feet in length as adults. The scientists mounted data-collecting devices on hammerheads that recorded speed, sonar and video data to reveal swim speeds, metabolic rates and prey encounters.

The team then used this data to build detailed computer models, comparing the energetic costs and benefits of hunting different prey types. The findings were striking. The models predicted that a 250-pound great hammerhead would only need to consume one 55-pound blacktip shark roughly every three weeks to meet its energy demands. This single large meal could sustain the hammerhead for up to two months during periods when blacktip shark populations are scarce. In stark contrast, if the hammerhead were to rely on smaller reef-associated fish, it would need to catch one or two 2.2-pound fish every single day to sustain itself.

“Animals must make careful decisions regarding how and what to hunt,” Papastamatiou said. “Do you go after large prey that have more energy but are harder to catch? Or should you just go after any potential prey you encounter? Here we apply these ideas to an incredible predator, the great hammerhead, and provide insight into why they might target large prey like other sharks or rays.”

Great hammerhead sharks are classified as critically endangered globally by the International Union for Conservation of Nature, facing threats from overfishing and habitat loss. Knowing their specific dietary needs and preferred hunting grounds is vital for developing effective conservation strategies that ensure their long-term survival, Papastamatiou said. The study also showcases the power of modern biologging and modeling techniques in studying large, difficult-to-observe marine animals.