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Guy Harvey

Before I moved to the Cayman Islands 11 years ago, my first close encounter with a great hammerhead shark was in the northern Bahamas. I was shooting a documentary on shark interactive programmes at Walker’s Cay, well known for the number of Caribbean reef sharks, black tip, lemon and bull sharks. We were chumming the bulls and lemons in shallow water at the north side of the cay when a huge dorsal fin came steaming up the shallows with a big bow wave…my first reaction was…Orca! But then common sense prevailed and I saw the unmistakable shape of the head as the 15-foot long animal cruised into the mix to investigate.

I quickly put on my snorkelling gear and headed back into the water. There were already a bunch of students there on a university shark field trip, having the time of their lives, in five feet of water with all these marvellous animals around them… and then a great hammerhead shows up! She came by close and picked up a fish head off the sandy bottom just a few feet from us, turned around and came back for another. In her turn, I could see the great girth of her body. She was carrying pups, nearly fully grown judging from her distended abdomen and her back was black having spent several days in the shallow water looking for the right spot to drop her pups. Yes, sharks in shallow water get sun burned.

It is good hear reports from the dive operators in Grand Cayman of frequent sightings of great hammerheads. This is not a common species, but because of the amount of diving conducted in the Cayman Islands encounters are much talked about. My first was at Tarpon Alley, a location where divers encounter other species on a regular basis such as reef sharks. Diving late in the evening is always the best time for an encounter, particularly near the channels through the reef into North Sound or at East End. Also early in the morning near the Sand Bar where all the stingrays have spent the night buried in the sand. If you are patient, and quiet, great hammerheads will be in the area trying to catch a careless stingray.

The great hammerhead is a cosmopolitan species, occurring in tropical and sub tropical waters worldwide. They are found in shallow coastal habitats as often as in an oceanic environment. I once hooked and released an 800 pound great hammerhead in deep water while trolling for black marlin off the Great Barrier Reef in Australia. Most angling experiences take place in shallow water often in association with fishing for other species. Anglers in Florida targeting tarpon, permit, jack crevalle or bonefish in skinny water have had the fun meter broken by seeing a huge dark shape materialize out of the green water and snatch their fish.

Great hammerheads feed on a variety of fish and rays as well as benthic invertebrates. I saw dramatic photos taken by a fellow Guy Harvey Research Institute researcher in Bimini of a great hammerhead chasing a spotted eagle ray and catching it. It used its horns or cephalofoil to pin the ray to the sand, and then spun its body around and bit off a wing so immobilizing the ray and eating the carcass. I imagine they do they same thing with stingrays.

Their flat, broad head or, the physical feature which distinguishes this family of sharks from all other species, is loaded with an array of sensory organs on the underside. This predator is able to detect hidden prey beneath the sand, and expose it and catch it. The cephalofoil gives them added mobility and the ability to make quick turns. In addition both eyes and nostrils are set far apart and scientists consider this as another advantage in locating prey species.

There are 10 different species of hammerhead shark, of which the great hammerhead grows the largest, reportedly up to 20 feet long. Other similar species such as the scalloped hammerhead and smooth hammerhead have a much more pelagic existence. The scalloped hammerhead is known to form large schools in the day time around seamounts in the tropical eastern Pacific and Sea of Cortez. The sites of these aggregations have been a diver’s Mecca for decades now and there are many studies being conducted on their migrations with a view to protecting these sharks from over-exploitation.

There are only two records of fatal hammerhead shark attacks on humans, but the actual species were not identified. This species is not a threat to humans in spite of their size. Most encounters with great hammerheads involve someone spear fishing, in which case the shark was attracted to the struggling fish and not the snorkeller or diver.

All species of hammerhead are targeted by commercial long lining activity for their large fins and livers. The scalloped hammerhead has taken the brunt of this fishing effort. The less common great hammerhead has been targeted by sports fishermen particularly in South Florida and many people have been shocked by pictures of very large pregnant females hung up for a photo. Hammerheads are known to grow slowly, reach maturity at around 100 pounds and litters can vary from a few pups up to four dozen pups in the very large females. This species is viviparous and gestation lasts 11 months and juveniles are fully formed miniature versions of their parents. The young sharks are born in shallow water to keep them away from their predators such as bull sharks, lemon sharks and reef sharks. It is time to protect these large individuals, which are the brood stock of a dwindling population.

There is a study on sharks in the Cayman Islands being conducted in a joint project by the Department of Environment, the Save Our Seas Foundation and The Guy Harvey Research Institute. Great hammerheads are a target species because so little is known about them. If you encounter this or any other shark species around the Cayman Islands please inform the Department of Environment about your experience and provide details of location and species encountered. More sharks are being tagged so we can learn about their habitat use and migrations.

It is our collective responsibility to conserve the marine environment and maintain the biodiversity of the planet. Fish responsibly, dive safely.

Guy Harvey PhD.   www.guyharvey.com