"First, you see is a stout round tower built by the British in 1844 - it was to help sailors navigate the reef. Then the bird smell hits. There's nothing like being down wind from thousands of nesting seabirds to invigorate the nasal senses," laughs Deb Maynard, crew member from Undersea Explorer, an adventure dive and research vessel based in Port Douglas.

Raine Island is a windswept, treeless, sand and coral cay located on the Great Barrier Reef about 60 miles north-east of Cape York Peninsula. "It's small and flat so you can't immediately see the land as the boat approaches," says Deb. "It's well known among researchers for the crowded breeding colonies of boobies, frigate birds, night herons and seagulls but we came to collect data on the annual sea turtle nesting and observe the tiger sharks.

"About 2000 female turtles struggle ashore each night. Incredibly, every one of them was born on the island - at least 50 years before; and they are guided back to breed by some kind of homing instinct.

"They stay in waters around the island with the males for about three months - mating, feeding and resting; and coming ashore about every 13 days to lay between 75 to 200 eggs.

"The eggs hatch in two to three months but very few hatchlings will survive to adulthood. Most are eaten by the nesting herons or other predators."

As National Parks prohibit people from going onto the island, Undersea's divers and researchers focus their efforts on offshore activity.

"We think there could be up to 20,000 sea turtles in the surrounding waters during the breeding season between October and November each year," says Deb, "and that they've probably traveled around 2,500 kilometres to get here.