Reef and Beyond

Tiger time

Every summer Raine Island becomes the world’s largest nesting site for green sea turtles. Up to 26,000 turtles have been recorded nesting in one night. This huge concentration of prey attracts a large number of tiger sharks. But they have a cunning tactical approach. The tigers attack surprisingly few turtles; instead they simply wait for the tide to bring them an easy meal.

Every night a few turtles die on the beach – falling over cliffs, being buried alive or simply dying of heat exposure. As the tide rises tigers swim across the reef flat circling the island – waiting for turtle carcasses to drift off.

Over twenty tiger sharks were observed here, all feasting on a single dead turtle – they all show amazing table manners – each takes a turn to feed on the carcass with their massive serrated jaws. Entering the water without a cage, team cameraman and marine biologist Richard Fitzpatrick filmed this spectacular feeding event demonstrating the social etiquette amongst large predators.
On one occasion the tigers became so persistent that Richard and his safety divers were forced to leave the water leaving their camera behind them.

'I’ve filmed tigers feeding on carcasses before but six at once was my new record. It was a challenge to keep track of the sharks while trying to film and as time went on, the sharks got bolder and would make the odd approach. Luckily I had a big camera between them and me. The trick with filming a feeding event like this is knowing when it is time to get out of the water,' recalls Richard Fitzpatrick

In addition to filming tiger sharks Richard has also been researching the annual migration of the tiger sharks to Raine Island for the past seven years. He has a unique way of catching these sharks to minimise stress – he catches them by the tail using a device he invented called the ‘claw’. This way a shark can be immobilised in a few minutes, tagged and released.

The tracking data shows that once the turtles leave Raine Island so do the tigers – they migrate thousands of kilometres in all directions of the compass. During the off-season they regularly pass close by Raine – using it as a fix on their mental maps. One individual shark was caught at the same location, same hour, 365 days later. The dive computer retrieved from the shark revealed that tiger sharks swim in a yo-yo fashion; diving from the surface down to a depth of over 350 metres and then back to the surface again every half an hour.

Image copyright: Richard Fitzpatrick