Each year, millions of hatchery-reared sea-run brown trout Salmo trutta L. (the sea trout) juveniles are released into the natural environment in the Atlantic region. The aim of this work was to investigate the growth responses of sea trout to changing temperature conditions and to compare the growth plasticity between wild and hatchery-reared fish. Scales were collected from sea trout in a selected river flowing into the southern Baltic Sea. We analyzed the scale increment widths as a proxy of somatic growth and investigated the interannual variabilities and differences in growth between fish groups (wild and hatchery-reared). We used mixed-effects Bayesian modeling and ascribed the variances in growth to different sources. Furthermore, we developed indices of interannual (2003–2015) growth variation in the marine and freshwater phases of the life cycle of the fish and analyzed the relationships between trout growth and temperature. Temperature positively affects fish growth, regardless of the origin of the fish. We observed stronger relationships between fish growth and temperature conditions in the marine phase than in the freshwater phase. Additionally, wild sea trout are characterized by stronger responses to temperature variability and higher phenotypic plasticity of growth than those of the hatchery-reared individuals. Therefore, wild sea trout might be better suited to changing environmental conditions than hatchery-reared sea trout. This knowledge identifies possible threats in management actions for sea trout with an emphasis on ongoing climate change.

The methods of the data collection are decribed in the paper published in Ecology and Evolution: Lejk A.M., Smoliński S., Ratke G., Martyniak A. (2021). Higher growth variability and stronger responses to temperature changes in wild than hatchery-reared sea trout (Salmo trutta L.).

Capture_year - the year of sampling

L_caudalis  - fish fork length (cm)

Weight - fish body mass (g)

Age_river - number of winters spent in the freshwater

Age_sea - number of winters spent in the sea

Increment_1_river - scale increment of 1st freshwater annual growth zone (accuracy ± 0.01 μm)

N_1_river - number of circuli

Increment_2_river - scale increment of 2nd freshwater annual growth zone (accuracy ± 0.01 μm)

N_2_river - number of circuli

Increment_3_river - scale increment of 3rd freshwater annual growth zone (accuracy ± 0.01 μm)

N_3_river - number of circuli

Increment_1_sea - scale increment of 1st marine annual growth zone (accuracy ± 0.01 μm)

N_1_sea - number of circuli

Increment_2_sea - scale increment of 2nd marine annual growth zone (accuracy ± 0.01 μm)

N_2_sea - number of circuli

Increment_3_sea - scale increment of 3rd marine annual growth zone (accuracy ± 0.01 μm)

N_3_sea - number of circuli

Increment_+_sea - plus growth at the outer edge of the scale (accuracy ± 0.01 μm)

N_+_sea - number of circuli

Group - hatchery or reared fish

Sex - 1 -male; 2 - female

Cohort - year of birth

Spawning_1year_before - presence of spawning mark one year before capture

Spawning_2year_before - presence of spawning mark two years before capture

FishID - individual fish number