Effects of environmental conditions experienced by parents, embryos and juveniles on later life history stages in Atlantic salmon

Temperature and food affect growth and age at maturity in poikilothermic animals. We demonstrated how increased temperature and fat content in food reduced age at maturity in Atlantic salmon. Food is like fuel for an engine and temperature is the accelerator of the engine. Temperature during embryonic development affects how fast salmon will grow later in life. Increased temperature during early development allows faster growth, make the fish store more reserve energy (fat), and develop larger eggs and gonads when sexually mature. In addition, high autumn temperature in the river has trans-generational effect by that the offspring produce larger eggs when they become sexually mature. Thus, in a moderate climate change, salmon adapts quickly through interactions between genes and environment (adaptive plasticity). There appears to be no other study showing a similar trans-generational effect on egg size by the thermal environment of the mother during the last month before ovulation. The future climate is expected to be characterized by increased precipitation, but also more severe periods of drought. This can effect the production of salmon. During 1976-2015, we have found that the production of juveniles in teh River Imsa increased with number of eggs spawned and minimum flow in August, the first year the offspring live in the river. Thus, higher minimum flow improved ofspring survival. The survival was however, negatively density dependent, but did not reach an asymptote. Climate change influences time of seaward migration of Atlantic salmon smolts. Since 1975, the smolts of the River Imsa migrated to sea 4.2 days earlier per 10 years. During the last 50 years, mean time of seaward migration has decreased by 2.5 days per 10 years over the Atlantic basin as revealed by analysis in 68 rivers. Although most smolts migrate downstream in April and May in the River Imsa, fish can descend to the river estuary any month of the year. However, young salmon descending outside the regular smolting period exhibited three times poorer survival than those descending in April-May. Those migrating downstream later than September appeared to stay in the river estuary until the subsequent spring before they moved to sea. Growth rate during the first year in the ocean has decreased by 40 % since the 1970s. The growth reduction correlates significantly with the increase in sea-surface temperature. However, sea surface temperature is only 1 °C warmer now than 100 years ago, which is little relative to the reduction in size. Only a reduction in energy consumption can cause such a large growth reduction in healthy salmon. Therefore, we hypothesized that the growth reduction is caused by reduced feeding opportunities for post-smolts in the North Atlantic. Post-smolts feed chiefly on pelagic amphipods. Age at maturity has changed during the same period. The proportion ofone-sea-winter salmon increased from the 1970s to 2000 and decreased again after 2000 and in particular after 2005. Both very poor and very high growth may influence the delayed maturation. We plan to test optimal age at maturity by life-table analysis.

By use of time series analysis and laboratory experiments this project will analyse effects of climate and habitat loss of the production of Atlantic salmon in a Norwegian index river. Specifically we will: 1) Study effects of climate at different times o f the year and loss of lake habitat on juvenile salmon production in the River Imsa. We will do this by testing effects of numbers of eggs spawned, water temperature and flow on recruitment, growth and juvenile production. Fish migration and environmental variables in the river have been monitored daily during 37 years. 2) Work out predictions for future changes in salmon production in the Imsa (2071-2100) by using the most recent climate scenarios. 3) Study epigenetic effects of thermal treatment of pare nts and embryos on offspring growth, age and size at migration in common environment experiments. The parental fish will be split in two groups: one kept at the ambient River Imsa temperature and one in 3° C warmer water from 1 October till egg fertilizat ion. Also, offspring groups of parental fish held in natural Imsa water will be divided in two: one reared in natural Imsa water, the other in 3° warmer water till hatching. Growth will be estimated at eight constant temperatures (range 6° to 24 °C) of of fspring of parents held at both elevated and natural Imsa water. 4) Study effects of thermal treatment of parents and embryos on growth at ambient temperature in sea water and the reaction norms for sea growth and age at maturation. The experiments in sea water will last until sexual maturation at age-2 years, when fecundity and mass of individual eggs will be measured. 5) Model how life-history variation due to climate change translates to population dynamics, specifically how it affects the population g rowth rate (r). There is good gender balance in the project, and the results will be disseminated in reports, peer reviewed scientific journals and popular science journals and directly to nature managers.