Migratory behavior and maternal origin of anadromous brown trout in the Baltic Sea

Abstract

In the Baltic Sea, brown trout have been shown to make extensive use of the marine ecosystem; however, little is known regarding their movements between freshwater and marine environments or the interactions between individuals at different life history stages within a population. First, we analyzed the otolith structure and chemistry of hatchery origin (n = 26) anadromous brown trout with known life history and maternal origin to evaluate the efficacy of otolith microchemistry to distinguish between freshwater habitat in northern Sweden and marine rearing in the northern Baltic Sea. We then described the maternal origin and migration patterns of wild anadromous brown trout (n = 59) originating from the Ume and Vindel River catchment in Northern Sweden. Otolith microchemistry revealed that the majority (73%) of fish made 3 or more (up to 5) migrations to the marine environment prior to capture, presumably to feed. We observed a high degree of life history diversity, where trout first migrated to sea from age-1 to age-4 and either migrated back to freshwater once each year (presumably to spawn) or spent more than 1 yr in the marine environment before returning to freshwater. While 42% of the wild anadromous trout were judged to be the progeny of a resident mother, sex ratio, age, and inter-habitat migrations were similar for resident and anadromous progeny, highlighting the role of resident life histories in producing anadromous adults. Results reported here provide managers with new information to support the protection and enhancement of brown trout populations in places where they have declined.