Sockeye salmon (Oncorhynchus nerka).  Adults migrating up the Adams River to spawn. (c) WWF-Canon / Michel ROGGO / feow.org

By Lewis Smith
March 31 2011

Climate change is causing migrating salmon to die from heart failure in their millions as they stretch every sinew to reach their spawning grounds.

Overheating is such a problem for the sockeye salmon that as they head for their traditional spawning grounds in the Fraser River network in Canada their hearts stop.

So many are being killed every year by the temperature rises associated with global warming that the sockeye salmon in some of the Fraser River tributaries are likely to become extinct.

“Their hearts just can’t cope with the temperatures,” said Erika Eliason, of the University of British Columbia in Canada.

The salmon, several million of which return to the Fraser River every year, are so driven to spawn that they simply keep on swimming instead of having a breather to cool down. They can swim up to 26 miles daily, almost the length of a marathon. “They don’t have the option to sit and wait and hope things cool down. They only have a tiny window [of time] to get to the spawning grounds,” she added.

It is the combination of exertion and warmer conditions that is proving fatal to the fish, scientists found. Since the 1950s the water temperature has risen by almost 2C and the sockeyes have been in steep decline for the last 20 years, which include several of the hottest years on record.

Up to 95 per cent of some local populations of the salmon have died during the migration upstream and researchers have demonstrated that they swim most efficiently in water cooled to the temperatures they would have encountered historically during the spawning migration. …

"Currently, the Fraser River's peak river temperatures during the summer months exceeds the optimal temperatures for every population we examined and temperatures are near lethal for some populations." …

Sockeye salmon hearts stopped by climate change

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