Some are just cold fish, others are hot strategists but all salmon have different personalities that affect how they hunt for food, writes Julia Hinde.
Researchers from Edinburgh and Glasgow universities, and the Freshwater Fisheries Laboratory at Pitlochry, have found from laboratory experiments that some juvenile salmon can be taught to recognise visual and smell cues signifying food. This ability, they believe, is used as a strategy by some young salmon in streams where the changing environment may mean there is a need to adapt and be flexible.
But the experiments also showed that other salmon, despite repeated demonstration, did not learn.
"It's not that they are stupid," said Felicity Huntingford, professor of functional ecology at Glasgow University. "Fish have different strategies in resource acquisition. They have different personalities."
Some are extremely aggressive and very successful at getting food in tanks but are inflexible, and others thrive far better in changing streams where they have to adapt.
"We really don't know where these differences come from but my hunch is that the fish are born that way. In an unpredictable environment parents would want to produce young able to deal with all environments, but that is quite complex. We think instead they produce a mixture, with some able to learn and be flexible and others that are aggressive and inflexible. This way the maximum number will survive," she said.
John Armstrong of the Freshwater Fisheries Laboratory in Pitlochry has been using electronic chips to follow the fish in the natural environment. He has found that individual juvenile salmon, which may spend up to the first eight years in their home streams before going to sea, inhabit very distinct areas. These may be overlapping, but some are noticeably much larger than others.