Hammerhead sharks are a group of nine species within the shark family; obviously named for their flattened, hammer shaped heads. Different hammerhead species are found worldwide; mostly preferring warmer waters along deep continental shelves. While most sharks tend to be fairly solitary creatures, hammerheads are normally solitary hunters at night only. During daylight hours, particularly at sunrise and sunset, they often swim in schools which can be encountered at a variety of locales, with popular hammerhead dive sites being located primarily in the Indo-Pacific and Caribbean regions.
Hammerhead Shark Facts
Hammerheads range in size from less than a meter to about 6 meters long, and can sometimes weigh more than half a ton. With white bellies and greenish-grey dorsal sides that are capable of tanning for protection from the sun’s rays, they have better vision than most other shark species and can see along a 360 degree plane. They are capable of seeing everything above and below them at all times, a trait that very few animals possess.
Like the rest of the shark family, hammerhead species have electroreceptory sensory pores; but these are spread out over a wider area than they are on most other species. This allows them to hunt more effectively, as do their nostrils, which are positioned further apart from one another. Besides having the capacity to detect tiny electrical signals as small as half a billionth of a volt, hammerhead sharks have a superb sense of smell and are capable of detecting and localizing various chemical components found in decaying matter and bodily fluids.
Hammerheads have small mouths for their size, often scooping up prey from the bottom rather than rising from beneath prey for a powerful attack as many of their cousins do. Favorite foods include squid, octopus, crustaceans, and stingrays, which they stun by pinning down onto the ocean floor with their heads before eating. Great Hammerheads are more aggressive than other hammerhead species, and have been known to cannibalize other hammerheads, including their own young.
Like some other sharks, hammerheads are viviparous, with females giving birth to live young after a violent mating ritual and a gestation period that lasts between 8 and 10 months. Litters of hammerhead pups usually number between 12 and 15, although great hammerheads usually give birth to 20-40 pups at a time. After birth, the pups school together and swim away from their mothers; there is no parental care provided. Baby hammerheads can be encountered in warmer, shallower water than adults can – but be cautious, as they will bite if provoked.
Pregnant female hammerheads are often very large, making them a target for trophy hunters. Recently, deceased pregnant sharks have washed ashore in Florida, with J-hooks still lodged in their mouths and gills. Necropsy revealed that one of these sharks was carrying 35 pups that were ready to be born, translating to a single sport fisherman causing the unnecessary death of 36 hammerhead sharks. Another fisherman caught a 1,300 pound female hammerhead with a 3 foot head span, which was later autopsied and found to be carrying 55 developing pups. While catch and release would have been the kinder, and more sensible option, the shark “had to be killed” to check to see whether her weight would break records. While the shark’s body was handed over to researchers for study, many wildlife activists are outraged that she was ever caught at all.
Diving With Hammerheads
Only three of the nine known species of hammerheads pose any danger to humans; these are Great Hammerheads, Scalloped Hammerheads, and Smooth Hammerheads. If confronted, they may respond by dropping their pectoral fins and swimming with stiff, jerking motions. As of 2011, the International Shark Attack File listed only 34 hammerhead attacks with one fatality. Less than half of those attacks listed were unprovoked.
Most hammerhead dives take place with schooling hammerheads being seen in the distance. These sharks prefer deep water and with the exception of juveniles, rarely come up into water shallower than thirty meters. In most places where schooling hammerheads are seen, divers position themselves along seamounts or reefs above the schooling sharks, and watch from above. In some places, the hammerheads will come into shallower water, but this is rare.
During seasonal migrations, schools of hammerheads can include hundreds of individual sharks. One of the best places to see huge schools of hammerheads is in the Galapagos, where migration patterns tend to be predictable and encounters are almost guaranteed. In the Cocos Islands, hammerheads can be seen all year, with sightings increasing during the rainy months of June-November; here, they are often encountered up close as they tend to visit cleaning stations in shallower water. During El Nino years, hammerhead sightings decrease, as the sharks head for deeper, cooler waters.
Other top sites for diving with hammerheads include Japan’s Yonaguni Monument, and Taiwan’s Green Island, where hammerheads can be seen schooling between January and March. During April and May they are seen in Malaysia at Layang Layang and other sites, and in the Bahamas, spectacular hammerhead sightings occur between December and April each year. You can see them in the Maldives, and if you go to La Paz, Mexico, you may be fortunate enough to encounter hundreds of hammerheads at the El Bajo seamount site. There are just a few of the best places to find and dive with these magnificent creatures; most of the sites are deep and are washed by strong currents.
Unfortunately, hammerhead sharks are overfished in some countries where they are targeted for their fins, de-finned, and thrown back into the water to die a slow, painful death. While they are not the only species to suffer this inhumane treatment, some hammerheads are now listed as vulnerable, while others are endangered species. Our oceans rely on these and other top predators, and humanity relies on our oceans; even for the air that we breathe. With careful conservation and education efforts, we can help to increase hammerhead shark numbers and pull them back from the brink. Shark fin soup? No thanks.