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What killed these giant fish?

A dozen white sturgeon died recently in a B.C. river. No one knows what killed them.

Nikolaus Gantner and a colleague begin dissecting an endangered white sturgeon found dead near Prince George, B.C. Necropsies of the animals weren't easy due to their significant size.Submitted by Nikolaus Gantner

Nikolaus Gantner is searching for clues in 12 mysterious deaths along British Columbia’s Nechako River.

It’s not your usual whodunnit.

The dead are white sturgeon, North America’s largest and longest-living freshwater fish. The species has been around for more than 200 million years, sharing the planet eons ago with dinosaurs.

While the white sturgeon population is endangered, premature deaths of the fish are exceptionally rare. Even more baffling, the dead fish — which were discovered in August and September on the Nechako River — were found with no wounds or telltale signs of what killed them.

Nikolaus Gantner is a senior fisheries biologist for British Columbia and has become the chief detective in an investigation into the deaths of the 12 dead sturgeon. (Georgie Smyth/CBC)

Gantner, based in Prince George, B.C., is a senior fisheries biologist for the province. Armed with a microscope and tissue samples from the fish, he’s become the chief detective in an investigation he says is equal parts devastating and perplexing, considering how closely monitored the population is.

“It was like going through grief because we’re really here trying to take care of this population,” he said.

“I went through all the phases of grieving.”

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Clues to the deaths now exist in dozens of vials and freezer bags holding tissue samples, awaiting analysis in labs across Canada. It could take months to solve the mystery.

Studies show there are about 500 white sturgeon left in the Nechako River, so a dozen deaths marks a significant blow to the numbers. Incredibly, almost zero wild sturgeon have been born in the river since 1967, according to Environment and Climate Change Canada.

There are several possible reasons for this and many can be traced back to the construction of Kenney Dam in Fraser Lake, B.C., according to the white sturgeon recovery strategy.

A changed river

The dam is part of a Rio Tinto-owned hydropower facility that feeds an aluminum smelter in Kitimat, B.C., more than 400 kilometres from where most of the dead fish were found. The dam, built in 1952, created the Nechako Reservoir, which diverted water into the Kemano River and away from the Nechako. The operation provides hydropower to about 350,000 B.C. residents, according to the company.

But the diversion of water influences the white sturgeon’s habitat by decreasing the natural flow of water. Long range monitoring shows the Kenney Dam has reduced winter flows on the river at Vanderhoof by 50 per cent and early summer flows by about 75 per cent, according to reports.

Research has connected environmental stress, like warmer water, to the species’ exceptionally low birth rates.

The Nechako Reservoir, behind the Kenney Dam, is shown. (Rio Tinto)

In a statement to CBC News, Rio Tinto said it was “aware” and “saddened” by the death of the 12 white sturgeon in the river and offered technical support to “identify the possible causes of this unprecedented event.”

The deaths of the 12 giant fish are yet another red flag for the health of the river, according to First Nations whose territory encompasses the Nechako.

The Saik’uz and Stellat’en First Nations, which have been fighting for years for improved conditions on the river, took Rio Tinto to court in a bid to have the flow of the river changed to mitigate damage from the dam. In January, a judge dismissed the suit against the company but the two First Nations have since appealed the ruling.

Vanderhoof

Kitimat

Nechako

Reservoir

Prince

George

Kenney

Dam

Kemano

Powerhouse

BRITISH

COLUMBIA

Pacific

Ocean

Vancouver

50 km

Dead sturgeon locations

Vanderhoof

Prince

George

Nechako

River

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©Mapcreator | OSM.org

Vanderhoof

Kitimat

Nechako

Reservoir

Prince George

Kenney Dam

Kemano

Powerhouse

BRITISH

COLUMBIA

Pacific

Ocean

Vancouver

50 km

Dead sturgeon locations

Prince George

Vanderhoof

Nechako River

10 km

©Mapcreator | OSM.org

Vanderhoof

Kitimat

Nechako

Reservoir

Prince George

Kenney Dam

Kemano

Powerhouse

BRITISH

COLUMBIA

Dead sturgeon locations

Prince George

Vanderhoof

Nechako River

10 km

Pacific

Ocean

Vancouver

50 km

©Mapcreator | OSM.org

Robert Michell, chief of Stellat’en First Nation, says the recent sturgeon deaths should be a wake-up call to non-Indigenous stakeholders.

“Not to us, but to the other side. To say, ‘This is what we’ve been talking about. This is exactly what was going to happen and more of it will happen until something gets done about the river,’” Michell said.

Robert Michell, chief of Stellat'en First Nation, stands by the Nechako River near Vanderhoof. When CBC visited on Oct. 4, parts of the bottom of the river bed could be seen from shore. (Georgie Smyth/CBC)

Ancient giants

Gantner remembers the first time he saw the “spectacular” Nechako white sturgeon.

The species, often described as looking like a shark, can grow more than five metres long and live for more than 100 years.

Seeing an ancient fish that is older and larger than a person is humbling, he says.

While the white sturgeon species is found throughout North America, the Nechako population is genetically distinct from others that reside even within the same watershed, like the Upper and Lower Fraser River populations.

Four populations of white sturgeon, including the Nechako and Upper Fraser, were listed as endangered under the Species at Risk Act (SARA) in 2006. The Nechako has the smallest population of endangered white sturgeon in B.C., according to SARA.

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B.C.'s white sturgeon are closely monitored by scientists, to track the health of the endangered population. So the deaths of the 12 fish came as a surprise. Clockwise from upper left: One of the dead sturgeon, found on the banks of the Nechako. Tissue samples taken from a dead sturgeon, to determine age, sex and where the fish spent most of its life. Nikolaus Gantner and his team measure a live sturgeon as part of regular monitoring. A live sturgeon is seen in the Nechanko River. (Submitted by Nikolaus Gantner, Georgie Smyth/CBC)

The sheer size of the fish is what helped Gantner and his colleagues locate most of the dead dozen, some via helicopter, when more reports of carcasses on the river were reported in mid-August, following a public call-out.

All the carcasses were found between Prince George and Vanderhoof, B.C., and seven were brought back, stored in large walk-in freezers, and eventually dissected. The samples taken from the fish were good quality because the remains weren’t too decomposed, but Gantner says performing necropsies on the sturgeon — some up to 2.5 metres long — was not easy.

Tissue specimens were taken from various parts of the fish, including the ear bone and fins, to determine age, sex and where the fish spent the majority of its life.

Preliminary analysis shows the dead were all males and were eating sockeye salmon before they died.

Looking for answers

Reports of dead white sturgeon on the Nechako have stopped, but questions remain about what caused the deaths.

Scientists have their suspicions.

Contamination in water or food, low water levels, higher water temperatures and low oxygen in the water are all being looked at.

WATCH | Scientists race to uncover why the white sturgeon are dying:

But some of those things had been occurring in the river for years before the fish deaths, leading scientists like Gantner to consider a wider range of possibilities.

“It may have been a perfect storm that led to their deaths,” he said.

It could be months until Gantner has answers. But Priscilla Mueller, chief of the Saik’uz First Nation, wants action on the river now.

Sturgeon once considered a delicacy

CBC News spoke to Mueller on the banks of the Nechako in Vanderhoof, B.C., where parts of the bottom of the river bed were visible from shore.

“Look at it. The sturgeon can’t survive in low levels in warm temperatures.”

Members of the Saik’uz and Stellat’en First Nation remember times when the white sturgeon were more plentiful. The fish weren’t a staple to the degree sockeye salmon were but they were a revered delicacy, according to chiefs Michell and Mueller.

“It would be a way of life for us. Our grandchildren and some of our children have no idea that we used to harvest sturgeon,” said Chief Mueller.

Priscilla Mueller, chief of Saik'uz First Nation, stands by the Nechako River near Vanderhoof, B.C. (Georgie Smyth/CBC)

The Nations say they are working to establish a better relationship with Rio Tinto and to eventually establish a river management plan alongside the provincial and federal governments to increase water flow to help the sturgeon.

For its part, Rio Tinto says its been working with First Nations and local communities “to improve the water flow into the Nechako River.” It operates under strict requirements from the federal Department of Fisheries and Oceans, it added in a statement to CBC News.

The future

While investigations continue into the mysterious deaths of the 12 white sturgeon, the bulk of conservation work focuses on mending their habitat and boosting numbers through a hatchery program.

Because the Kenney Dam blocks the natural flow of the river, the Nechako no longer experiences a significant spring freshet. The loss of that seasonal event, which would flush the river of sediment, means its banks have become clogged with silt and sand, says Steve McAdam, a biologist with B.C.’s Ministry of Land, Water and Resource Stewardship.

The debris fills in critical crevices where white sturgeon larvae used to settle before hatching.

The Kenney Dam, at left, was built on the Nechako River in the 1950s. The water behind the dam forms the Nechako Reservoir. Water from the reservoir is diverted away from the Nechako River and into the Kemano River to power an aluminum smelter in Kitimat, hundreds of kilometres away. Downstream, at right, water levels near Vanderhoof were too low to launch a government research boat when CBC News visited on Oct. 4. (Georgie Smyth/CBC)

The change in the river bed is one of the issues contributing to ongoing reproductive issues that led to the creation of the Nechako White Sturgeon Conservation Centre, according to the White sturgeon recovery strategy.

“We call them interstitial spaces for them to go and hide in, their survival rate goes way up,” said McAdam. “If those spaces are gone … the larvae would drift downstream.”

The hatchery is located metres from the only known spawning ground of the Nechako white sturgeon, near a bridge in Vanderhoof. It rears baby sturgeon to about 70 centimentres in length before releasing them in the spring into the same river as the wild population.

A baby white sturgeon from the Nechako White Sturgeon Conservation Centre. The fish are kept in large tanks until they are big enough to be released into the Nechako River. (Georgie Smyth/CBC)

Given the population’s low birth rates and the aging adults in the river, these efforts are crucial to keeping the species from going extinct, says Mike Manky, the hatchery’s manager.

In an ideal world, he says, his job would not exist.

“Success for me is putting myself out of a job in 20 years,” he said.

Mike Manky holds precious wild white sturgeon eggs taken from a female caught in the Nechako River. Manky is the hatchery manager at the Nechako White Sturgeon Conservation Centre in Vanderhoof, B.C., and says there’s a lot of pressure to get the science right, given how dire the situation is for the species. (Georgie Smyth/CBC)

Among the last tasks for Manky’s team before that stretch of river freezes over for the winter was finding a wild pregnant female to bring back to the conservation centre.

The female would be kept in river-like conditions mimicking the river and would spawn at the centre.

Despite the odds of finding one, the team recently pulled in a large pregnant white sturgeon, with hundreds of precious eggs that should hatch in the spring, potentially giving the population the boost it desperately needs.


With files from Susana da Silva

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