A Royal Marine from Devon has joined a multi-service team undertaking a daring mission off the coast of Costa Rica.
Sgt Gareth Thomas from Plymouth is in the Cocos Islands with divers from the Army, Royal Navy and Royal Air Force to electronically tag hammerhead sharks.
The major in charge of the expedition says the team will gain experience working in threatening situations, as well as helping a conservation project.
Sgt Thomas has been a professional diver for 20 years.
"Sharks are in dramatic decline around the world and this is our chance to make a difference "
"They want us to put GPS transmitters on the fins of the hammerheads and hopefully that's what we're going to do.
"I've dived with sharks before. A lot of them are actually scared of humans, but of course there's some apprehension because with any wild animal, they can turn round and bite you at any stage."
Major Andy Reid says the aim of Exercise Jurassic Shark is to develop leadership, teamwork, courage and co-operation which is vital to military operational capability.
Once the hammerhead sharks have been successfully tagged, their movements will be tracked to help determine their migratory routes.
Major Reid said: "Sharks are in dramatic decline around the world and this is our chance to make a difference by establishing those parts of the shark's habitat that most need protection."
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