Chilcotin landslide presents new barriers for struggling salmon

An expert on British Columbia’s salmon populations says the massive landslide that blocked off part of Canada’s largest sockeye salmon run has created an unprecedented situation, potentially putting the already struggling fish at even more risk.

Scott Hinch, associate dean at the University of British Columbia’s Pacific Salmon Ecology and Conservation Laboratory, said the debris piled 30 metres high and 600 metres long that’s blocking the Chilcotin River in B.C.’s Cariboo region could cause problems for chinook and sockeye populations — both while the water is being held back, and when it eventually bursts free.

“These are natural events, but what’s unusual about this event is it’s occurring at a time when the rivers are way warmer than they used to be,” he said in an interview Thursday.

“And that creates this unprecedented lack of understanding of what’s going to happen to these fish.”

The sockeye are on their way to Chilko Lake, where they will spawn. But to get there, they have to get through Farwell Canyon, around 285 kilometres north of Vancouver, where the dam of rock and mud is in the way.

Dangerously warm water

Officials with the province and Cariboo Regional District say it’s uncertain if the lake building behind the dam on the Chilcotin, a tributary of the Fraser River, will burst or if it will top over the debris.

The B.C. government said a release could swell the Fraser for hundreds of kilometres, potentially setting off dozens of emergency evacuations and alerts.

Hinch said the warmer Fraser River is already nearly lethal for the salmon, and it could be dangerous for the fish if they get held back from entering cooler glacier-fed waters.

“So, what’s happening right now is, with the reduced water flow downstream, that water is going to be warmer as a start. It’s also going to possibly be less accessible,” he said.

“So, these fish are going to be holding in warmer water and low flows, either in the Chilcotin system or in the Fraser system.”

Williams Lake First Nation Chief Willie Sellars said the situation with the salmon run is “incredibly concerning.”

He said the First Nation is worried about what will happen to the fish after the large lake pooling behind the landslide breaks loose.

“What is that going to do to every single one of those sockeye and chinook that are swimming up the Fraser River looking to spawn in those other tributaries?” he said.

Debris could create new barriers

Hinch said one of the problems is there’s no way to know how the debris sent flowing down the rivers will eventually settle.

“If not full barriers, it could create partial barriers, it could create areas where it’s more difficult for the fish to get around,” Hinch said.

“Keep in mind that these fish have all stopped feeding about a month ago. And so, they’re migrating up on reserves.”

There’s also a risk that new rock and debris in the water could affect the salmon’s ability to navigate using their sense of smell, a skill imprinted on them as fry.

“They are imprinted on unique chemicals that are in their home watershed. That chemical composition is disrupted by landslides, because you now have other organic chemicals coming into the river, at high concentrations, that aren’t part of their home stream smell,” he said.

Sellars said this was already anticipated to be a low-run year.

“Maybe it’s better that something like this happened on the low year, but then it’s also pretty devastating to that run that’s going to be heading up the Chilcotin, and four years from now there is going to be no fish,” he said.

At a news conference Thursday, Minister of Water, Land and Resource Stewardship Nathan Cullen said the government knows that the water is critical spawning habitat for salmon and other fish and that the government was “initiating early plans as to what we can do to make sure that those stocks remain intact.” 

But Hinch said there’s not much that can be done prior to the dam breaking.

“All we can do is hope that the temperatures that these fish are holding in isn’t doing irreparable damage to them for too long of a period of time. And that the fish get into the Chilcotin once the river is amenable for migration.”