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Sydney - Sharks whose babies eat each other in the womb may not be everybody's idea of a species worth worrying about, but Australian scientists are desperately trying to save them from themselves.

Government researchers are working to develop an artificial uterus in which grey nurse shark embryos can grow without being cannibalised by their siblings, shark scientist Nick Otway told AFP Thursday.

The female grey nurse starts her pregnancy with more than 40 embryos in her two uteruses, but by the time they are ready to be born up to a year later, there are only two left - one in each uterus.

All the others have been eaten through what Otway calls "intra-uterine cannibalism", a gruesome trait unique to grey nurse sharks.

"By the time the embryos get to about 10cm long at around four months, they have a fully developed, functional set of jaws and they begin to cannibalise their siblings.

"That's the whole problem with this animal really," he said. "It's such a bizarre reproductive strategy that anything over and above that that causes deaths in its environment will cause the population to go downhill."

The grey nurse shark, which grows to around three metres , is classified as critically endangered on Australia's east coast and as vulnerable worldwide, Otway said.

With the sharks only producing two pups every two years the surviving local population of just a few hundred "top of the food chain predators" is under serious threat of extinction.

So the scientists at Australia's Cronulla Fisheries Centre have turned to modern technology for help in saving the species which has been around for some 70 million years.

Otway and a team of colleagues plan to catch pregnant grey nurse sharks, flush out the embryos before they can start eating each other and raise them in tube-shaped tanks serving as artificial uteruses.

They are developing an artificial uterine fluid to match the real thing, but much research and work remains to be done, he said.

It could be five years before the first high-tech shark is released from an artificial uterus, but if it works "it will be a world first," Otway said.

"If we can raise about 40 pups a year it will start bringing up the grey nurse population."

No accepted explanation has been established for why the grey nurse sharks take sibling rivalry to such extreme lengths.

"It would seem logical that the intra-uterine cannibalism does confer some sort of evolutionary advantage, somewhat similar to the survival of the fittest, but it may be the luck of the draw because even the biggest could be attacked," Otway said.

The survivors of the pre-birth bloodbath are not known to attack humans.

Source - Sapa-AFP