Sprinting Salmon Face Tragic Deaths

Researchers have found that burst swimming or "sprinting" among salmon can lead to the fish having heart attacks mere feet from their spawning grounds, journeying so very far only to tragically die near the very end.

Traditionally, when fish like the sockeye salmon encounter fast and turbulent water - such as parts of river just downstream of a dam - they launch into a swimming "sprint," fighting the rapids and trying to get to calmer water as fast as possible.

This makes for some fantastic imagery, with the determined fish valiantly climbing their way up a seemingly impassible obstacle. It is also the same behavior that allow fish ladders - man-made steps that lead fish around modern dams - to work.

However, this action can have a tragic effect on some salmon.

"Days after sockeye passed through extremely fast-moving water, we started to see fish dying only a short distance from their spawning grounds," Nicholas Burnett, a research biologist at the University of British Columbia said in a recent release.

Burnett and a team of his colleagues found that this burst swimming for too long creates a build-up of stress metabolites like lactic acid in the blood, and may lead to cardiac collapse or heart attacks.

They also found hat female salmon, which are essential for the spawning process at the end of the hard migration, were more likely to experience this "delayed mortality," supporting past theories that female salmon are more sensitive to environmental hardships.

"We now understand how this important but energetically costly swimming behavior can impact the survival of sockeye during their upstream migration," said Burnett. "Our work demonstrates how important it is for salmon to have easy access around obstacles in the river."

Obstacles, he says, like dams and their resulting rapids, need to be somehow circumvented if conversationalists want salmon populations to remains strong and healthy in the years to come.

The study was published in Physiological and Biochemical Zoology.