Two die-offs of over a thousand pink salmon were seen recently in the Tsolum River in the Comox Valley, amid severe drought conditions throughout Vancouver Island.
With the pink salmon run underway, the Tsolum River is being monitored by local stewardship groups, including the Tsolum River Restoration Society and the K’ómoks First Nation Guardian Watchmen.
The first die-off was seen on Aug. 24, when over 1,000 dead pink salmon were documented clustered around one location along the river. Then another 1,200 or so dead salmon were seen at the same spot on Aug. 29.
Vancouver Island’s drought conditions — now ranked at level 5 or most severe — looks to be the driver of these die-offs, said Caroline Heim, program coordinator with the Tsolum River Restoration Society.
“The main issue is there’s just not very much water in the river — low flows — so therefore, the fish are having trouble moving up and there are bottlenecks,” said Heim. “The fish are getting stacked up behind these bottlenecks, they use up all the available oxygen, and then they just die.”
One such bottleneck was caused by a log jam just upstream of the die-off location, which the K’ómoks Guardian Watchmen later helped to remove. While such obstacles are making it harder for the salmon to move upstream amid low water levels, some are reaching an upstream hatchery, said Heim.
“They’re not completely stuck, but there’s a lot of obstacles to get over when the flow is so low,” she said. “Fish are getting through, but there’s just so many that some are not going through fast enough.”
The die-offs are happening in the evening, when water temperatures are highest. Such die-off events have never been seen in the Tsolum River over the past 20 years the society has operated, said Heim.
“It’s never happened in my memory; we’ve never noticed this before,” she said.
The Tsolum River lacks flow control structures, such as dams, so there is little the Department of Fisheries and Oceans (DFO) can do to prevent these die-offs events under current conditions, said Cate Barratt, DFO communications advisor, in an email.
Heim is asking anyone with a water license on the river to stop drawing water from it if possible.
“That’s the only thing that can be done,” she said. “It’s time to conserve water if you have a water license.”