On the factors affecting migration and straying in brown trout (Salmo trutta)

Abstract

Anadromous brown trout display a continuum of life-history strategies with high intraspecific variability across their distribution range. While many of these strategies have been widely studied, some have received considerably less attention. In this study, we investigated intraspecific differences in two overlooked life-history strategies—outmigration phenology (spring vs. autumn migrants) and the prevalence of straying—in brown trout originating from four rivers flowing into the same fjord system. Juvenile brown trout ( Salmo trutta) were tagged with passive integrated transponder (PIT) tags in their natal river, and were subsequently followed during their outmigration and subsequent return to freshwater. We found that patterns of outmigration (spring vs. autumn migrant, day of season) and return to freshwater (return likelihood, strayers vs. nonstrayers) differed between rivers, as did the factors (length, condition) affecting these outcomes. We also found evidence that outmigration phenology was linked to the likelihood of returning in a river-specific way. Our findings suggest that the costs and benefits of autumn migration and straying differ depending on an individual's home river.