Rising water temps threaten B.C.’s famed sockeye salmon run

Dangerously high water temperatures in the Fraser River in British Columbia are posing a huge threat to the region’s renowned sockeye salmon run.

The warm waters, which neared 20 C on Tuesday, combined with record low river levels could mean a massive die-off of returning Pacific sockeye salmon swimming up the Fraser River to spawn.

“The fish will simply not make it to the spawning grounds if the temperatures are too high, which means they’ll never have the opportunity to spawn because they only spawn once in a lifetime,” says Anthony Farrell, a zoologist with the University of British Columbia in Vancouver. “To not be able to get up the Fraser River to their native watershed is catastrophic.”

Conditions are so dire the federal government has been forced to temporarily ban all sport fishing in streams throughout the south coast and is considering halting commercial fisheries. Mike Lapointe, chief biologist for the Pacific Salmon Commission, told the Maple Ridge News that it is “certainly possible” that sockeye fisheries could be curtailed or even cancelled because not enough fish survived to reach the spawning grounds.

“Above a certain temperature fish don’t have sufficient energy to swim, so once you start getting into 18, 19, 20 degrees [Celsius] their athletic capabilities fall off,” says Farrell. “At some temperatures they will have no swimming abilities and cannot swim at all, so there’s no hope for them to be able to swim against the Fraser River, in some cases going 600 or 1,000 kilometres.”

Usually water temperatures in the Fraser River in August range around 15 C, nearly 5 degrees cooler than what has been seen this week. The optimal temperature for salmon ranges from 3 to 15 C.

In addition, very little snow in B.C. this past winter means that what little snowpack in the mountains has almost all melted, leaving less available to keep water levels up and temperatures down as the summer progresses. Without an injection of melted snow water temperatures could continue to rise, making fish more susceptible to illness and infection.

According to Fisheries and Oceans Canada, at 18 C sockeye salmon demonstrate decreased swimming ability and at 20 C, they begin to die at a high rate. At prolonged exposure to water above 21 C they suffer severe stress and early death.

“Once you get above 18 or 19 degrees, fungus and bacteria that are natural in the watershed grow much faster,” adds Farrell. “Any tissue damage to the fish or its gill is prone to infection and when it’s very severe, the gills can completely clog up with fungus and the fish suffocates.”

Pacific salmon are a unique species in that they are born in freshwater, migrate to the ocean and then return to freshwater to spawn and then die. Some swim as far as 1,000 km to return to their native stream.

Within the Fraser River watershed there are many genetically distinct populations of sockeye salmon, and each population enters the river to swim upstream at a specific time. Most runs occur between June and October.

Whether this year’s spawning season is a success hinges greatly on the weather, and industry experts are hoping for rain, clouds and cooler temps. The provincial government has estimated that 6.8 million sockeye salmon will return to the Fraser River this year, a figure far below the 20 million sockeye that returned last year and the record 30 million recorded in 2013.

Pacific sockeye salmon only spawn once in their lifetime, which makes the threat of a massive die-off all the more worrying.

“A large-scale die-off this year would primarily affect the run size four years from now (when this year’s offspring will be returning to spawn). Certainly, a large-scale die-off this year could result in very low numbers of returning fish four years from now, which is a major conservation concern,” says Erika Eliason, a zoologist and research associate at the Ocean Tracking Network.

There is hope that over time, Fraser River salmon could adapt to cope with warmer temperatures.

“The big question is whether they can adapt quickly enough to keep pace with climate change,” she says. “Current peak river temperatures already exceed the functional thermal tolerance for every sockeye salmon population studied to date. As a result, many populations are already in big trouble.”

A failed salmon run this year will likely mean higher prices for sockeye salmon at the store. Researchers at UBC have said they expect salmon prices to increase by a possible 70 per cent per pound over the next 35 years as populations plummet.