New research shows that salmon can identify their most common predators, simply on the basis that that predator has previously eaten salmon. Even young fish can do this, despite never having encountered that particular predator before.

Researchers from the University of Swansea put young Atlantic salmon in tanks of water, some sections of which were scented with diluted otter faeces. They found the fish tended to avoid the scented water – provided the otter in question had previously eaten salmon.

The smell acts as an early-warning system for the fish, even when they can’t see the predator. It lets them work out the potential risk of being eaten and balance predator avoidance with other vital activities like foraging and reproducing.

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Planet Earth online (12 Sep 2011)

BBC Website (19 Sep 2011)