Sockeye salmon hearts stopped by climate change .. EYE Report

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

Article found HERE By Lewis Smith March 31 2011

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.

One group of sockeyes, however, have been dubbed ‘superfish’ by scientists who found that while having to complete the most demanding salmon run in the river network they seem to be impervious to climate change.

In the Fraser River network the sockeye salmon return to the spawning grounds where they were born and those from the Chilko lake and river have stronger hearts than their close cousins from other tributaries. It has meant that while the fish from Chilko are coping well with the temperature rise of almost 2C since the 1950s, those from the Weaver Creek and Nechako region.

The key to their success is thought to be the extreme evolutionary pressures on them over thousands of years. They have the hardest run of all the salmon in the Fraser River network and have swim more than 400 miles inland and up an elevation of three-quarters of a mile, meaning it is only the fittest and strongest which can survive.

“These guys can do a marathon a day – that’s upstream against the current,” said Ms Eliason who carried out the study, reported in the journal Science, with colleagues from the University of British Columbia and the Simon Fraser University.

Salmon, which like other fish are the same temperature as the water they swim in, are finely tuned to their environment small changes in temperature can significantly affect their efficiency. The sockeyes from Chilko were found to have extra adrenaline receptors in their hearts which allowed them

to cope better with temperature changes. There are more than 100 distinct populations within the Fraser River network.

Ms Eliason added: “Chilko were able to swim at higher and a broader range of temperatures compared to the other populations we examined. We believe it has to do with how they’ve adapted to cope with their difficult 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.”