Environment | Daily Report

alinnigan/ FlickrReduced populations of sockeye salmon may be the result of climate change.

Dams, pollution and overharvesting aren't the only things threatening Pacific salmon populations.

Climate change may be taking its toll as well.

Scientists testifying in front of an international government panel investigating the decline of sockeye salmon in British Columbia's Fraser River said nearly half the returning salmon die before they get to the spawning beds.

And the scientists blame the death rate on warmer water temperatures. The Fraser River’s temperature has increased by about two degrees in the past few decades, and according to researchers, that’s enough to change the timing of the fish’s spawning migration. 

Scott Hinch, an aquatic biologist at the University of British Columbia, said the warmer water doesn’t kill the fish directly, but it does increase their stress load. For instance, salmon use more energy to swim and get oxygen when in warmer water, and this extra exertion could lead to exhaustion and cardiac arrest.

Warmer water also promotes disease growth – bacteria, viruses, fungi – which can affect the salmon.

Pete Rand of the Wild Salmon Center in Portland, who was not at the inquiry, said the climate concern is not unique to sockeye in the Fraser River. He said all Pacific salmon, from California up to Alaska, are at risk.

In California and Oregon, “the very southern part of their range, they are very sensitive to increases in water temperature,” he said. “Many of the rivers will likely exceed tolerated levels.”

But Harry Morse, a spokesman for the California Department of Fish and Game, said it would be difficult to point to just climate change as the chief factor in salmon decline. 

“There was a national science panel that looked at the Delta situation, and a National Oceanic and Atmospheric Administration panel and a Pacific Fish Management Committee, and they have all said there is a cornucopia of 40-plus factors that deal with the decline in salmon,” he said. “None of them are putting high emphasis on climate change. There are just so many thing happening in California, with the redistribution of water and dams.”

He also said that the Fraser River situation isn’t as cut and dried as some scientists would make it.

“There are lots of opinions on the Fraser,” he said. “Not everyone agrees with each other.”