Do Hammerheads Follow Magnetic Highways in Migration?

Brian Handwerk
for National Geographic News
June 6, 2002

Sharks Photo Essay: Go >>

As a young researcher, Peter Klimley decided that it was not only safe but also important to dive freely among hammerhead sharks to acquire a better understanding of the magnificent animals. "I believe you can learn about 80 percent of what's going on in the natural world by observation," he said in a recent interview.

Some people feared disastrous consequences of such a venture. Instead, it put Klimley on the path to becoming a leading shark expert.

Klimley, of the Department of Wildlife, Fish, and Conservation Biology at the University of California–Davis, has been studying hammerheads and their behavior for more than 20 years. His observations of their elaborate social rituals and communication have considerably expanded knowledge of one of the most distinctive sharks.

There are nine species of hammerheads, which range from three to 20 feet (one to six meters) in length. They are found in the tropical and subtropical waters of oceans around the world. Klimley's current research project focuses on hammerhead sharks' little-known migration habits—knowledge that's important for the conservation of the sharks, and perhaps other marine species.

He is looking closely at the curious tendency of hammerheads, as well as other organisms, to school in large groups around underwater mountains. "Since the mid-80s," said Klimley, "I've been arguing that there is a whole assemblage of species that move north and south via stepping stones," or seamounts.

Underwater Schooling

For more than 20 years Klimley has been studying the behavior of scalloped hammerheads at underwater mountains, or seamounts, such as El Baho Espiritu Santo in the Gulf of California. There, he has observed breathtaking numbers of the sharks.

Why they create such a striking spectacle is not completely understood.

One thing that seems clear is that the sharks are not gathering at such locations because seamounts are a source of abundant food. In fact, the hammerheads gather at the seamount during the day but feed elsewhere at night. They leave the area at night—alone or in small groups—and spread out through the ocean for miles to feed on fish and squid.

Using ultrasonic telemetry, Klimley has tracked this feeding behavior. His research showed that at a certain time in the early morning, the sharks return to the seamount, generally following the same paths with remarkable regularity. They seem to use the underwater mountain as a kind of base.

Klimley thinks that the gathering of hammerheads around a seamount and the sharks' movements in the waters beyond may be related to their response to magnetic fields, made possible by the presence of electro-receptors at the bottom of their uniquely shaped heads.

Continued on Next Page >>


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