Predator tiger sharks can turn into marine scavengers too

Known as impressive predators that hunt and consume almost anything from birds to sea turtles, tiger sharks can easily play the role of marine scavengers when the opportunity presents itself, say researchers.

This behaviour was reported in Springer's journal Behavioral Ecology and Sociobiology by a team of American, Australian and British researchers led by Neil Hammerschlag of the University of Miami Rosenstiel School of Marine and Atmospheric Science in the US.

They re-evaluated satellite tracking data collected from tiger sharks and green turtles off the Great Barrier Reef's Raine Island, which is home to the world's largest concentration of nesting green turtles.

The researchers found that during the nesting season of turtles, tiger sharks spend the greater part of their time patrolling surface waters close to shore instead of remaining in deep water as they do when actively hunting, suggesting they are on the look-out for carcasses or weakened turtles that end up in the water.

Green turtles also did not show any signs of the behaviour they typically use to avoid sharks, such as reducing their time at the surface, despite the presence of tiger sharks.

These observations suggest that tiger sharks are not likely to be hunting healthy turtles during the nesting season, despite the opportunity to do so.

"For any predator, hunting and capturing prey is energetically demanding and inherently dangerous," Hammerschlag said.

"At Raine Island, although sharks can encounter and hunt thousands of healthy green turtles, the large numbers of dead and dying animals that get washed into the water during the nesting season makes it far more profitable for the sharks to scavenge on these carcasses rather than to chase live turtles, given the possibility of wasted time and energy when predation attempts are unsuccessful," Hammerschlag noted.

This energy-saving switch in behaviour to scavenging when faced with an abundance of food is not just typical of sharks, but also of predators such as hyenas and lions in terrestrial systems.

--IANS

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