Reef sharks like their food bite sized

Don't let the sharp teeth fool you because coral reef sharks eat more like snappers than great whites.

That's according to researchers from James Cook University (JCU), who pumped the stomachs of more than one hundred white-tip, black-tip and grey reef sharks and found none were eating big prey.

Instead, they found the remains of animals like molluscs, sea snakes and fish, often no larger than a cheeseburger.

"The surprise to me was that such a big animal is eating such small fish," lead author Dr Ashley Frisch told AAP.

"We assumed they were the apex predators but it turns out they're not."

Dr Frisch says reef sharks are occasionally eaten by bigger shark species like tigers or hammerheads.

And, tissue analysis found they had similar diets to larger coral fish like snapper and emperors, he said.

"So rather than eating big fish, reef sharks are eating like big fish," he said.

Scientists say understanding who eats who on the reef will help predict the affects of population changes.

More than half the sharks to have their stomachs pumped had nothing in their guts at all, indicating they eat infrequently and opportunistically.

Dr Frisch said the results were further evidence coral reef sharks, often seen by snorkellers and divers, were not a threat to humans.

"Anyone swimming in the water with the reef shark is pretty safe," he said.

The research, from JCU's ARC Centre of Excellence for Coral Reef Studies, was recently published in the journal Coral Reefs.