Local variation in stress response of juvenile anadromous brown trout, .

Habitat fragmentation may cut off anadromous salmonids from parts of their potential native habitat and separate previously connected populations. Understanding the consequences of this is vital for fish management and prioritization of restoration activities. Here, we show that there is a significant difference in the body morphology, physiological stress response, and aspects contributing to aerobic capacity between juvenile anadromous brown trout, , collected at a downstream site and an upstream site, separated by 2 km and several challenging stream sections, in a small unfragmented stream system in western Sweden.

Variation in phenotypic plasticity across age-at-maturity genotypes in wild Atlantic salmon.

Evolution of phenotypic plasticity requires genotype-environment interaction. The discovery of two large-effect loci in the vgll3 and six6 genomic regions associated with the number of years the Atlantic salmon spend feeding at sea before maturation (sea age), provides a unique opportunity to study evolutionary potential of phenotypic plasticity. Using data on 1246 Atlantic salmon caught in the River Surna in Norway, we show that variation in mean sea age among years (smolt cohorts 2013-2018) is influenced by genotype frequencies as well as interaction effects between genotype and year.

Temporal shifts in the marine feeding of individual Atlantic salmon inferred from scale isotope ratios.

Given the limited information on prey use during the marine residency period for Atlantic salmon, scales were collected from salmon at return to the River Namsen (Norway) for spawning after 1 year at sea, and scale material from the first and second summer marine feeding periods was analysed using stable isotope methods to understand dynamics of their trophic ecology. As the salmon increased in size from the first to second summer, they reduced their feeding niche and specialised more (narrowed the δC range) and increased their dependency on higher tropic level (δN) prey, likely fish. Changes in δC indicated a consistent pattern of movement towards the north and west between summer feeding periods.

Brown trout (Salmo trutta L. 1758) and Arctic charr [Salvelinus alpinus (L. 1758)] display different marine behaviour and feeding strategies in sympatry.

Brown trout (Salmo trutta L. 1758) and Arctic charr [Salvelinus alpinus (L. 1758)] tagged with acoustic transmitters migrated from fresh water to the sea mainly in May and June, but with large individual variation in migration timing.