Repeatable individual variation in migration timing in two anadromous salmonids and ecological consequences

Consistent individual differences in behaviour has been demonstrated for many animals, but there are few studies of consequences of such repeated behaviour in the wild. We tested consistency in migration timing to and from the sea among anadromous Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta), using data from a study period of about 25 years, including more than 27,000 uniquely Carlin-tagged individuals that migrated to sea for feeding in the spring and returned to the river in late summer for up to 13 successive years. Consistency was found between individuals across time in timing of the seaward migration. Individuals migrating early during their first migration tended to migrate early the following years, and late migrants tended to migrate late. The same pattern was found also at ascent to freshwater. Hence, this study demonstrated that individual fish in nature can differ in behaviour related to migration timing, and that these differences can be consistent during...