Getting into hot water? Atlantic Salmon responses to climate change in freshwater and marine environments

Recent and projected climate changes – both in the freshwater and marine environments exploited by Atlantic salmon – present considerable adaptive challenges to many populations. In assessing the predictions and possible impacts of overall climate change, we focus in freshwater on precipitation, river discharge and temperature, whilst for the marine environment we highlight the interactions between temperature, size/growth-mediated predation and shifts in prey assemblages. Changes in seasonal temperature and flow regime probably will exert complex or conflicting interactions for particular river stocks in terms of freshwater survivorship, growth, smoltification and timing of emigration. Ocean temperature changes will directly affect early post-smolt survivorship and indirectly influence prey availability and hence longer-term survivorship, growth, maturation and spawning run-timing. It is of immediate concern that most salmon stock abundances presently are at historical lows, but perhaps the greatest uncertainty in projecting their future health lies in our poor understanding of the genetic and ecological adaptability of populations in relation to the likely rate(s) of environmental change. Against the backdrop of a rapidly changing environment, a precautionary approach to managing salmon populations should be holistic and integrative of both the marine and freshwater environments, and should include the maintenance of their genetic variability and integrity.