Differential response to a competitor by Atlantic salmon adopting alternative life-history strategies.

The life cycle of the Atlantic salmon is extremely variable. In good growing conditions, juvenile salmon either metamorphose into the migratory phase by their second spring, or delay this for at least another year. The strategy appears to be decided in their first summer. This study compared competitive responses of fish adopting the two strategies. Laboratory experiments showed that the two types of fish had similar foraging efficiencies in isolation. However, although a simulated competitor had little effect on the feeding behaviour of fast-developing fish, it caused an 18-fold increase in the incidence of failed feeding attempts by fish delaying development. The probability of an attack failing was dependent on how close the competitor came.