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What Is Killing the White Sturgeon of the Nechako River?

The discovery of eleven carcasses has spurred researchers to seek the public’s help in solving a mystery.

Amanda Follett Hosgood and Josh Kozelj 13 Sep

Amanda Follett Hosgood is The Tyee’s northern B.C. reporter. Josh Kozelj is a Hummingbird fellow with The Tyee.

Nikolaus Gantner spent a lot of time last month cruising the Nechako River in a jet boat looking for dead sturgeon.

His searches began when he received a message from recreational paddle boaters on Aug. 11 that one of the big bottom feeders, its lineage stretching back millions of years, had been found dead on a bank of the Nechako. Gantner, who says he has long held “a fascination for a dinosaur living among us,” took an interest also because he is senior fisheries biologist for the Omineca Region at the Ministry of Forests.

After finding the first sturgeon carcass, Gantner wasn’t particularly concerned. But the next week, eight more were reported dead in the river between Vanderhoof and Prince George, where the Nechako flows into the Fraser River.  

Gantner has never known so many of the fish to die in those numbers over so short a period along the Nechako. He learned of the mounting toll from members of the public and through an aerial survey conducted by the Department of Fisheries and Oceans. There was no time to waste. Carcasses can wash away and decompose quickly before biologists can determine a cause of death.

Gantner and his team of colleagues tracked down ten sturgeon corpses in a little over a week, until finally there was one more to get — a mammoth two-metre fish weighing around 100 kilograms. 

They hauled it into the boat and wrapped it in a tarp before transporting the sturgeon to a walk-in freezer in their Prince George lab that Gantner says “is getting filled up pretty quickly with the full-sized fish.” The last giant joined six others in the freezer. The remaining four were too old to bring into a lab but samples have been collected.

But the specimens yielded few clues immediately. There were no obvious net scars. No hooking injuries. Or wounds. 

And so the race is on to figure out what is killing the Nechako white sturgeon in suddenly large numbers. And to find out whether those deaths in B.C. are tied to other spikes in sturgeon losses in Idaho, California and other places.

The mystery is being tackled by a network of sturgeon researchers who are enlisting the help of the public. Last week the province put out a call asking people to report any dead sturgeon sightings in the Nechako region.

An ancient creature already endangered

The white sturgeon of the Nechako River are a genetically distinct population whose survival has already been labelled tenuous. They stay mainly in the Nechako River, sometimes venturing into the Upper Fraser. Unlike its neighbours in the Fraser River, the Nechacko white sturgeon is experiencing “recruitment failure,” or the inability to reproduce in the wild, as a result of impacts to the watershed, according to Steve McAdam, a biologist with B.C.’s Ministry of Land, Water and Resource Stewardship who has studied the fish for more than 20 years.

Nechako white sturgeon is among four sturgeon populations in B.C. listed as “endangered” under Canada’s Species at Risk Act. Other populations with the designation are in the Upper Fraser River, Columbia River and Kootenay River.

“I think the fact that the Nechako fish are SARA-listed really does heighten the concern,” McAdam said.

The Nechako river sits beside a sand embankment.
The Nechako River near Prince George. The surge in discovered dead sturgeon along its waters coincides with other spikes in sturgeon mortality in Idaho, California and elsewhere. Photo via Shutterstock.

From 1994 to 1999, the provincial government closely studied the Nechako white sturgeon, concluding the species was in a critical state of decline. A collective was founded — the Nechako White Sturgeon Recovery Initiative — to investigate why. The groups involved in the recovery initiative include the B.C. Ministry of Forests, Saik'uz First Nation fisheries program and Rio Tinto — a mining company that constructed a dam in the 1950s that altered the flow of the Nechako watershed. 

Today there are believed to be roughly 500 adult Nechako white sturgeon, most of which were born prior to 1967, when the fish’s ability to spawn naturally sharply declined, McAdam said. The fish have a lifespan similar to humans, often living 80 years and occasionally beyond 100.

The recent surge of sturgeon deaths is cause for worry, based on data collected since the ‘90s, said Gantner. “I think for the last 20, 30 years while we’ve had the recovery program in place and a close eye on the population we haven’t had an adult mortality like that.”

Other regions have seen higher than normal white sturgeon mortality this summer, including the Lower Fraser River, where up to 20,000 adult sturgeon live. McAdam says this year’s toll on the Lower Fraser is the highest since summers of 1993 and 1994.  

What’s to blame? Could it be higher than normal water temperatures and low oxygen levels? Those factors were cited by Idaho’s Fish and Game department when 20 white sturgeon died in the C.J. Strike Reservoir last month.

“It’s a concern,” said McAdam, but the situation on the Nechako likely is more complicated. “We have hot years, and fish didn’t die. So, what’s the combination of factors? In terms of why they are dying, I think the answer is we don’t know yet, because we really need to go and look at the fish.”

‘Death by a thousand cuts’

Nicholas Demetras is a fisheries biologist with the University of California Santa Cruz, who has been puzzling over rising sturgeon deaths in the San Francisco Bay Area over the past few years.  

This year a harmful algae bloom killed thousands of fish, many of them sturgeon.

But like McAdam, Demetras emphasized that researchers are unlikely to identify a single smoking gun. “It’s death by a thousand cuts,” Demetras said. “We did see a noticeable uptick in reported sturgeon carcasses that coincided at the same time as these harmful algal blooms.”

Demetras works in collaboration with university colleagues and government resource agencies — and with the help of citizen scientists. His team has reached out to beachcombers, amateur naturalists, kayakers, birdwatchers, sport fishers and others to provide the organizations with information about any dead sturgeon they come across.

The researchers also get reports from iNaturalist, an online network where naturalists can log their observations.

“The public was very receptive to it and we’ve since gotten quite a few reports,” Demetras said, adding that they have received close to 100 reports of dead sturgeon a year, although some are likely duplicates.  

“Now it’s really to the point where we want to know what’s causing it,” he said. “That’s the hard part. Now we need some really directed studies to do that.”

The difference between the recent red tide event and what’s happening in the Nechako, Demetras pointed out, is that white sturgeon in the Bay Area live in brackish water while Nechako white sturgeon — and other populations in the Fraser watershed — remain exclusively in freshwater.

But they face many of the same threats. In addition to algae blooms, some of the contributing factors Demetras identifies — such as environmental pollutants from agricultural runoff and changes in spawning habitat due to dams — are also seen on the Nechako River.

Mike Manky, Freshwater Fisheries Society of BC hatchery manager, samples an adult sturgeon last fall in the Nechako River.
Nechako White Sturgeon Conservation Centre hatchery manager Mike Manky with a living sturgeon collected during a sampling effort in September 2021. The hatchery is ‘a stop gap solution’ to the fact the species is endangered, says Manky. ‘They seem to survive better after release, so it seems to be working.’ Photo by Fraser Linza, Freshwater Fisheries Society of BC.

“It pains me to see them dead here in California and it makes me even more concerned when I get these reports from Oregon, Washington and British Columbia. I would like to see a lot more research done and a lot more money directed towards research,” said Demetras.

“Sturgeon are amazing animals,” he said. “They’ve been around for 260 million years. They were here 100 million years before the iconic T-rex. They’re quite resilient, but we’ve highly modified the landscape.”

All the endangered-listed white sturgeon populations in B.C. swim in habitats altered by dams, noted McAdam. The Kenney Dam blocked flows into the Nechako River in 1952, redirecting two-thirds of the river’s volume west toward the Kemano generating station, which powers Rio Tinto Alcan’s aluminum smelter in Kitimat.

While the downstream effects weren’t immediately obvious, the dam affected seasonal water flows, caused river temperatures to rise and created erosion that distributed sediment into the river, clogging sturgeon and salmon gravel spawning beds.

While the dam is largely blamed for the crash in natural white sturgeon spawning that began in 1967, other factors also need to be considered, according to researchers at the University of Northern British Columbia.

A loss of vegetation on the landscape — from things like logging and increased wildfire activity — has led to greater erosion and more sediment in the river, and climate change has also impacted the watershed.

Researchers are working to study changes to habitat in the Nechako River and repairing the damage to gravel spawning beds. In the meantime, the population is propped up by the Nechako White Sturgeon Conservation Centre’s sturgeon hatchery in Vanderhoof, which releases juvenile sturgeon into the river once they reach two years of age.

“The idea behind this facility is to be a stop gap solution,” says hatchery manager Mike Manky. “They seem to survive better after release, so it seems to be working.” 

As of Sept. 12, Gantner had received no new reports of sturgeon dying in the Nechako but efforts to get to the bottom of the mystery haven’t diminished. He and his colleagues expect to take samples within the next two weeks in pursuit of more clues. 

Gantner invites anyone along the Nechacko to join the effort. “We don’t have eyes on the whole river at all times,” he said. “Every single fish we can get our hands on, relatively fresh and not too decomposed, we can maximize what we can learn from that fish.” 

Echoes McAdam: “If people see a fish, we want to hear about it.”  [Tyee]

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