Proc. Natl Acad. Sci. USA 104, 9715–9719 (2007)

Credit: GETTY

Entire populations of North American rainbow trout are at risk of extinction as water temperatures rise with climate change, causing multimillion dollar impacts on commercial and recreational freshwater fisheries, a new study finds.

Peter Biro of the University of Technology, Sydney, Australia, and colleagues studied experimentally created trout populations in British Columbia, Canada, during two consecutive years, with eight and nine replicate populations, respectively. In 1998, lake temperatures were several degrees warmer than optimal for trout growth (21–22 °C), whereas 1999 temperatures were near optimal (17.5 °C). Only half as many young trout — about 4% in total — survived 1998, as compared with 1999.

Young trout forage near the shoreline to avoid predators, while seeking to attain sufficient growth to survive winter. Their metabolism increases as the water warms, however, requiring them to eat more to achieve the same weight. But the more they swim in search of food, the more susceptible they are to predation by adult trout, the researchers found. The study is the first to analyse climate impacts on the survival of geographically isolated fish populations, and identify the physiological and behavioural mechanisms responsible.