Sharks play dead before they're even born

Posted by Kate Taylor

Embryonic sharks, still within the egg, can sense danger and freeze toavoid being detected by predators, say marine scientists at the University of Western Australia.

The discovery, they say, could be helpful in the development of more effective shark repellents.

According to marine neuroecologist Ryan Kempster, the baby sharks can sense predators' bioelectric fields through electroreceptors on their heads.

And the team found that - even within their leathery egg cases -brown-banded bamboo shark embryos can sense electric fields that mimic a predator and stop moving their gills to avoid detection. If the threat carried on so long that they had to move, they did so to a much smaller degree.

"Despite being confined to a very small space within an egg case where they are vulnerable to predators, embryonic sharks are able to recognise dangerous stimuli and react with an innate avoidance response," says Kempster.  

Interestingly, the team found that when the embryonic sharks experienced the same electric field over a long period of time, they appeared to become habituated to it, and reacted less than before.

"This knowledge may help us to develop effective shark repellents," says Kempster. Creating electric shark repellents that change their signal regularly might make them more effective.