TAGGING HAMMERHEADS

If facing 3m-long sharks doesn’t quicken your pulse, what will? BSAC diver Major Andy Reid reports on an ambitious project to tag scalloped hammerheads at Cocos Island

You are at 25m, the swell is pushing you violently from side to side, and ahead of you is a small school of hammerhead sharks, slowly circling through a cleaning station marked by a number of bright yellow barberfish. Using all the stealth you can muster you slowly approach the sharks, trying desperately not to spook them. As you get closer you prepare your speargun for firing and position yourself as close to the cleaning station as possible. Suddenly, a 3m-long female passes about a metre in front of you. There is no time to think twice. You fire the gun – hitting her just below the dorsal fin. The shark swims lazily away, seemingly unperturbed by the experience. Little does she know, however, that she is now sporting £3,000 worth of satellite tagging equipment just below her dorsal fin. This was a typical day for divers taking part in Exercise Jurassic Park, a British military expedition to Cocos Island, 330 miles off the Pacific coast of Costa Rica, in July this year. The aim of the expedition was to electronically tag a number of the scalloped hammerhead sharks, which famously gather in their hundreds in these waters. Drawn from across the Armed Forces who are all members of BSAC clubs, our 14-strong Joint Services Shark Tagging Team (JSSTT), worked in association with the Shark Research Institute (SRI) and Costa Rican non-governmental organisation Programa Restauracion Tortugas Marinas (PRETOMA). Our base for three weeks was the Undersea Hunter liveaboard. Scalloped hammerhead numbers at

Cocos are thought to have declined by 70 per cent. Sadly, however, hard scientific evidence is needed before any significant moves can be made to protect them. Juvenile scalloped hammerhead sharks have never been seen at Cocos Island, which means they are almost certainly breeding somewhere completely unprotected – the hammerheads of Cocos could well be in far greater peril than most people realise.

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Aside from the local issue of protecting the sharks of Cocos Island, the results from our tagging project would help inform the scientific basis for the Eastern Pacific Tropical Seascape Initiative, which brings together the islands of the Galáápagos, Gorgona, Malpelo, Cocos and Coiba in a single conservation plan. Five major ocean currents, including cold water from Antarctica, and three tectonic plates converge in the area, creating a migratory

path for a large number of species. The ultimate aim of the conservation groups is to build up complete coverage of the movement of pelagic animals and, of course, afford the areas identified as migratory corridors a degree of protection. Before our team headed off on the expedition, there were many uncertainties about how successful our efforts would be. Many of us thought that the tagging of free-swimming hammerhead sharks simply couldn’t be done. Hammerheads are notoriously nervous animals, and even the team members couldn’t envisage getting close enough to them. Yet the expedition was remarkably successful – our final tally of 15 tagged sharks is thought to be the most hammerhead sharks ever to be tagged on a single expedition. Being close enough to a hammerhead to tag one (as close as 1.5m away) evokes many emotions, but fear is never one of them. Experiences such as this only serve to heighten the sense of frustration that sharks from Cocos and around the world are being killed in order to make nothing more than a bowl of rather tasteless fin soup. Cleaning stations occupied by small yellow barberfish (of the butterflyfish group) were the key to the team’s success. These stations appear to be the main reason for the high levels of hammerhead activity around the island. The sharks spend the night feeding in deep water and then come up to the cleaning stations during the day in order to have their parasites removed by these tenacious little fish. Entering these areas, the sharks slowed and often

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All photographs Major Andy Reid
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Main photograph, left, one of the team sets his sights on a scalloped hammerhead 1 the previously large numbers of hammerheads at Cocos are in decline 2 the expedition team and helpers 3 a new radio receiver and an old one encrusted with marine life 4 hammerheads are killed for their fi ns 5 Cocos Island lies 330 miles off the Pacifi c coast of Costa Rica 6 choppy waters at Cocos

rolled over to one side while waiting to be cleaned, rather like a dog inviting someone to tickle its tummy. The trick was for us to wait for the hammerheads to swim into a cleaning station and then move in slowly to tag them using a speargun. Rebreathers, which produce no bubbles, were used by some of the team in order to get as close to the sharks as possible. The sharks we encountered generally reacted to being tagged with a surprising degree of lethargy. One female, however, took exception to our advances and snapped our spear tip to show her disgust. Later found out she had good reason for her bad temper – the tag had gone straight through her body just below the dorsal fin! Fortunately, she suffered no ill effects and soon went about her usual business without distress. The only other signs of aggression was when Sergeant Gareth Thomas of the Royal Marines found himself fending off a group of sharks with his speargun when approaching one particularly feisty group. As well as the satellite tags, the team also deployed two new radio receivers at different sites and retrieved data from two previously deployed radio receivers. These record the presence of a radio tag when the shark swims past – logging the movements of a tagged shark as it moves around the island. Of the 15 sharks our divers tagged, ten were tagged with radio tags and five with satellite tags. The satellite tags are designed to read the temperature, depth and approximate location experienced by the shark every one to six minutes for periods

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of up to 120 days. The tags eventually release from the shark and download this information to a satellite. The radio receivers provide information about the sharks in relation to specific sites, whereas the satellite tags will indicate where they go to feed and breed. It is vital to know this, because the sharks almost certainly leave the 12-mile protection zone. The team was also able to make a much more immediate and practical difference to the conservation of sharks. An illegal fishing boat was found close to a seamount first discovered by Jacques Cousteau and named after one of his boats, Alcyone. The fishing boat was well inside the 12mile exclusion zone and had clearly set long lines within a few hundred metres of Cocos Island’s best dive site. We photographed the boat, together with the GPS position and subsequently reported it to the national park headquarters on the island. PRETOMA also filed an official complaint. Long lining is an indiscriminate killer of sharks and other animals, which has yet to be completely stopped around the island and is a massive problem for the long-term future of Costa Rica’s shark fishery. Diving conditions varied from benign to extremely challenging, as the requirements

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of the project meant that the team had to dive some of the more seaward sites in bad weather. This resulted in strong currents and difficult surface conditions. Our only real concerns were about the bad conditions. When the waves reached more than 2m in height the boat could not see us at the surface – a worrying thought when you are 330 miles from the Costa Rican mainland! The worst aspect of the weather, however, was undoubtedly the rain. Cocos Island experiences an amazing 900cm of rain per year and most of it seemed to fall during our expedition! Scalloped hammerheads are not the only sharks to be found around Cocos Island and we were given the opportunity to dive without our spears on a few occasions. The night dive on the inside of Manuelita Island must qualify as one of the best night dives in the world. Here, white-tip reef sharks have learned that the lights of divers can be a significant advantage when hunting at night. Such is the population of these sharks that literally hundreds of them converge on the lights carried by divers. These are truly heavyweight sharks in comparison with hammerheads and often passed within touching distance as they swam in figures of eights around their cleaning station. Exercise Jurassic Park was so successful that the diving team is already planning a much bigger expedition to tag sharks at a number of different locations as part of the Eastern Pacific Tropical Seascape Initiative for 2008. We can’t wait to go back. For more information see the expedition website at www.jurassic-shark.org.uk. ■

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