The Fraser River is heating up because of climate change and an increasing number of salmon are dying in the warmer water from diseases or parasites or are simply dropping dead from cardiac collapse, a federal judicial inquiry has been told.
Scott Hinch, an expert witness on aquatic ecology, told the Commission of Inquiry Into the Decline of Sockeye Salmon in the Fraser River that sometimes 50 per cent of the salmon that return to the river die before they reach the spawning beds.
Dr. Hinch said because the Fraser has increased in temperature by about 2 degrees C, salmon are changing the timing of their spawning migrations, to enter rivers weeks earlier or later, in an effort to avoid warm water. And once in the river they are seeking out cold-water refuges, sometimes going up tributaries to sink to the bottoms of lakes or schooling where cold streams enter the Fraser.
As water temperatures continue to climb (predictions suggest an increase of between 2 and 4 degrees over the next 60 to 80 years), more and more Fraser River salmon are likely to die before they have a chance to spawn, said Dr. Hinch, a fisheries researcher and professor at the University of British Columbia.
"Certainly we're gong to see higher en route mortality [in the future]" he said. "We're going to have to forsake more harvest on these fish."
Dr. Hinch said the warmer water doesn't kill fish directly, but once the temperature of the Fraser has climbed above 18 degrees C, as it does for several weeks every summer, the fish are subject to stresses which increase the chances of death.
A paper Dr. Hinch and his UBC colleague, Eduardo Martins, prepared for the commission states salmon use more energy to swim and get oxygen in warmer water and can die from exhaustion or cardiac arrest before reaching the spawning beds.
Higher water temperatures also increase the rate of development of pathogens, exposing salmon to disease.
The research, one of 12 scientific papers being prepared at the request of Commissioner Bruce Cohen, says the phenomenon of en route loss of salmon was first reported in 1992 for three distinct runs of sockeye, which come back to the Fraser in the spring, early summer and summer. A fourth run of sockeye, which returns to the river in the fall, didn't exhibit the problem until 1996.
The paper states that since 1996 "en route loss of at least 30 per cent has been observed for at least one run-timing group in each year," and many stocks have had losses of 50 per cent or more.
Dr. Hinch did not estimate how many salmon may have died in total, but the paper states that in some years "hundreds of thousands of Fraser River sockeye salmon have died during their migration."
The Cohen Commission was ordered by Prime Minister Stephen Harper after a disastrous sockeye collapse in 2009, when only about one million returned to the river, instead of the 10 million predicted.
That collapse, the nadir of a 20-year downward trend in Fraser sockeye stocks, was followed last year by one of the largest returns on record, when an estimated 30 million salmon returned. The research paper says "variability in climate conditions" may explain the wild population swing, and it notes ocean conditions were more favorable when the run of 2010 was at sea.
Dr. Hinch and Dr. Martins, who synthesized decades of salmon research in their paper, said warmer water temperatures appear to be decreasing the survivability of salmon at nearly all life stages, not just when the fish are adults returning to spawn.
But Dr. Hinch said there is "shockingly little information" on the early life stages of salmon.
He also noted that one run of sockeye, which goes up the Fraser and then into the glacial-fed Chilko River, have adapted to handle dramatic temperature ranges.
He said it is important to protect a wide variety of salmon stocks, because it is not clear which fish may hold the genetic key to survive in the warmer water of the future.
Ernie Crey, a spokesman for the Fraser Valley Aboriginal Fisheries Society, said outside the hearings that coldwater streams flowing into the Fraser should be protected because salmon need refuges from warm water.
"None of these streams enjoy any special status in relation to the survival of salmon," he said. "Developments … like small power projects to generate electricity, roads or water diversions could easily compromise these small coldwater streams."