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Early sightings of a dugong, or sea cow, were probably responsible for the myth of the mermaids. But their numbers are declining rapidly. The expedition headed to the Bazaruto archipelago, nine miles off the coast of Mozambique, to investigate the very last sustainable population of dugongs - which are related to elephants - in the western Indian Oceanhttp://i.dailymail.co.uk/i/pix/2008/10/17/article-1078507-0224CEC8000005DC-117_634x405.jpg
One of the team's divers observes a shoal of jacks circling with balletic precision. This behaviour is a source of much debate, but is thought to be a defence mechanism against predators
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A giant manta ray, known to have the biggest brains of all fish, spotted off the south coast of Mozambique. In the background lurks a shark
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Despite the size of male sperm whales - which can reach up to 16 metres in length - sightings are rare. But when you see one, it's worth the wait
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Huge sunfish are indigenous to the Sea of Cortez, a strip between the Baja California peninsula and mainland Mexico, 60-130 miles wide and 995 miles long. These giants can grow up to six metres long
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None of the dive team had ever seen a weedy sea dragon, found only in kelp forests. But Philippe Cousteau and Tooni Mahto struck lucky at Fortescue Bay, on the east coast of Tasmania
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