Biomedical subjects
N B Metcalfe
Publications and source records attributed to N B Metcalfe.
Early social status and the development of life-history strategies in Atlantic salmon.
Atlantic salmon have a variable life cycle. In good growing conditions, underyearling fish may metamorphose into the migratory smolt phase during their second spring, or delay at least a further year. The strategy adopted by particular fish appears to become fixed during their first summer. This paper examines whether either feeding efficiency or dominance in mid-summer correlates with the life-history strategy adopted. Eighty fish were individually marked and their feeding efficiency (= mean handling time for food items) and dominance rank measured under laboratory conditions in mid-July. Growth rates of the fish were then monitored over the next three months, until developmental strategies became apparent. Discriminant and logistic regression analyses revealed that both dominance rank and size attained by July were independent, significant predictors of future developmental pattern (the age at metamorphosis being correctly predicted on the basis of rank and size in 84% of cases) whereas feeding efficiency had no effect. Thus fish that were dominant or larger two months after first feeding or both had a greater probability of migrating after only one year in freshwater than those more subordinate or smaller or both.
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.