Canadian researchers have trained sea lions to take part in an experiment designed to find out why the species is dying out.

The team strapped cameras and tracking equipment onto endangered Steller sea lions to see how they dived for food.

Early results from the project indicate that overfishing might not be the main factor in their decline as had previously been thought.

Male Steller sea lions measure 3m (10ft) and weigh more than 950kg.

This makes them the biggest of all sea lions.

These marine mammals once thrived on the shores of the North Pacific ocean. Now their numbers have dwindled to around 100,000. But no one knows why they are dying out.

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