Hammerhead sharks can be recognized by their flattened, rectangular-shaped heads suggesting a hammer. The nostrils, as well as the eyes, are located on the outer edges of the head. As the hammerhead swims, it swings its head back and forth through the water like a mine sweeper, possibly increasing the chances of detecting food. These sharks are found in tropical and subtropical waters and the favorite food of some species includes stingrays. The dark olive colored great hammerhead, the olive colored brown scalloped hammerhead, and the mouse-gray bonnethead are all types of hammerhead sharks.

Scalloped hammerheads seem to include both migratory and resident populations. In Natal, South Africa, they form schools of migrating individuals that move towards the pole during summer. Others form stable resident populations, such as those located in the East China Sea. While schooling behavior is unusual in sharks in general, scalloped hammerheads have often been observed in schools as large as 40 individuals. This behavior off the El Baja and Las Animas seamounts in the Sea of Cortez was investigated in depth by A. Peter Klimley and Donald R. Nelson of Scripps Institute of Oceanography. They found that as many as 500 hammerheads migrated to congregate off shore over various nearby seamounts during daylight hours, then separated at night, only to return again during the day. The reasons that scalloped hammerheads come together at these seamounts is still basically a mystery. While none has absolutely been ruled out, all of the standard reasons such as feeding, mating, protection and defense, and grouping as a swimming advantage against currents, have all been studied and seem unlikely. One theory is that the sharks are “refuging” – schooling and resting near food sources by day and possibly feeding at night in groups. The sharks also exhibit unusual and distinct social behavior during the daytime, clearly jockeying with each other for dominant social position. Hammerheads are very timid and easily frightened by divers using scuba gear. They are also thought to be moderately dangerous to humans, especially at night. These are some of the reasons that make their behavior so difficult to study.