Where to dive with hammerhead sharks

What they are

The hammer-shaped head, called a cephalofoil, is the trait that sets these sharks apart. In the great hammerhead the front edge of the head is straight and square to the body.^1,4

NOAA Fisheries gives the scalloped hammerhead's size as up to 11 feet and 335 pounds, and an Australian fisheries report gives a maximum of 346 cm total length. The great hammerhead is much bigger, reaching 550 to 610 cm, though about 400 cm is more typical for a mature adult.^1,2,3

Where and when divers see them

Scalloped hammerheads live in coastal warm temperate and tropical seas worldwide, from the intertidal zone to at least 275 metres deep. The species is known for gathering in large schools, a habit that also makes it more vulnerable to fisheries.^1,2

A tracking study at Cocos Island in the eastern Pacific found that scalloped hammerheads form large aggregations around the island, mostly by day, leaving around dusk and returning near dawn, presumably to feed in open water at night. Sharks there regularly pass through permanent cleaning stations, and fewer were present early in the year, especially in March.⁵

The great hammerhead is a coastal-pelagic and semi-oceanic shark found in warm temperate and tropical waters, from near the surface to over 80 metres. It is generally solitary, and some populations migrate seasonally towards cooler waters.^3,4

Conservation status

Both main species are listed as Critically Endangered globally on the IUCN Red List, according to Australian government shark reports that cite the assessments; the scalloped hammerhead assessment is credited to Rigby and colleagues in 2019. In Australian waters both are assessed as Endangered.^2,3

In the United States, the Eastern Pacific and Eastern Atlantic populations of the scalloped hammerhead are listed as endangered under the Endangered Species Act, and two other populations as threatened.¹

How to behave around them

We found no code of conduct written specifically for hammerheads. General guidelines for diving with sharks from the ReefQuest Centre for Shark Research advise letting a shark approach on its own terms, keeping still, ideally on or near the bottom, and staying close to your buddy.⁶

• Do not chase, corner, grab or touch a shark in any way.⁶
• Avoid staring straight at a shark if you want it to come closer.⁶
• Do not use bait or try to feed sharks underwater.⁶
• Great hammerheads are large and unpredictable, and the Florida Museum advises treating them with caution.⁴