Salmon at risk from warm Okanagan waters
Fortunately for Pacific salmon, the current heatwave isn’t as long or intense as last summer.
However, they will face a huge challenge from warmer water as they begin their long migration to the Okanagan, says Dr. John S. Richardson, a professor in the University of British Columbia’s department of forest and conservation sciences.
“The water in the chain of lakes in the Okanagan Valley is starting to warm up after a cool June with a late freshet. What a difference a month makes; folks are beginning to enjoy warmer water reaching into the mid- to high-20s °C,” he said Monday.
“Most of our Pacific salmon are very sensitive to warm temperatures and do not survive long in warm water. For the sockeye salmon that might be heading back into the South Okanagan, they will have to try to get through that very same warm water that everyone is enjoying,” he said.
“In fact, sockeye are at their limits when temperatures hit 20 C or just above. Not only are they at or beyond their heat tolerance, they
have to exert themselves swimming upstream for hundreds of kilometres. In the Columbia River, and even in the Okanagan River, there are also many dams that they have to pass. Even with fish ladders, it is exhausting.”
Scientists have studied the survival
of migrating fish after navigating fish ladders compared to some fish given a free ride in a tank in the back of a truck, he said. “Having to swim up those fish ladders has a cost and can result in higher death rates.”
Fortunately, fish can find relief in a few locations, he said. “In some cases, the fish can find tributaries flowing into the Columbia River with slightly cooler water and that can give them a break. Deep water in some reservoirs may be cooler than the surface. Especially in lakes, the bottom waters provide a refuge from warm surface waters.”
However, there are not many deep lakes on the way to the South Okanagan, he noted.
“Last year was a whole other story with hot water and freshwater ecosystems. This year is less extreme, but the longer-term trends are still bad for cool-water species like salmon. Hotter, longer summers with less water in the streams is not a good prospect for the future of salmon in the Columbia and Okanagan rivers.”
The good news is 2022 appears to be a good year for sockeye adults returning to freshwater from the Pacific, he said.
“When you hear about sockeye salmon making their way back to the South Okanagan, it really is a wonder that they can get there and we should be impressed with their efforts. While humans play in the warm water, remember that salmon do not enjoy it.”