Hammerheads in the shallows

Bimini in The Bahamas has become world famous for providing the opportunity to dive with – and photograph – great hammerhead sharks in provisioned dives to the west of the island. The sandy seabed at a depth of 10 metres (30 feet), seen through crystal-clear water, is immediately recognisable in the images posted by hundreds of photographers who flock to dive with the hammerheads.

When they are not spending afternoons posing for photos at the provisioning site, the great hammerheads of Bimini are more reclusive, shying away from boaters and snorkellers as they cruise the shallow flats looking for their natural prey. Our teams come across them only two or three times a year in the course of their standard research, but thanks to transect flights off the south of our island we know that these chance encounters are nowhere near indicative of the real number of hammerheads. In the space of a month, flying 20 minutes per day and three or four times a week, we sighted eight hammerheads in a two-square-kilometre area. The fact that these sharks routinely swim along underwater ledges looking for prey and at depths of only 0.5–1 metre (2–3 feet) indicates a more natural reason for the time they spend at Bimini and gives us insight into their habitat use. Having followed up by deploying receivers in three new locations, we expect to learn more…