According to a study reported in the news pages of the journal Nature, one type of killer whale, or orca, has been found to dine on shark and as a result their teeth become worn right down to the gums.

'Offshore' killer whales were first identified in the late 1980s. Finding out what they preferred to eat presented a challenge for researchers as they feed at depths of hundreds of metres. The fact that they were feeding was given away by the blobs of pink meat that floated to the surface. Genetic testing of this meat confirmed that they were the remains of at least 16 Pacific sleeper sharks.

Examination of dead stranded orcas and museum specimens showed that the average offshore orca has worn its teeth right down, exposing their pulpy centres – a giveaway on their abrasive choice of food.

'It may be that the young whales have to do most of the work. The older ones are probably just gumming away at the liver,' commented Ford, the author of the study.

The original study is at: www.int-res.com/abstracts/ab/v11/n3/p213-224/