Sudden death of endangered sturgeon alarms Canadian biologists | endangered species

WAfter a tall, armor-clad body was first seen in the fast-flowing Nechako River in early September, Nicholas Gantner and two colleagues set out on a jet boat, braving strong currents to investigate the dismal discovery.

Days later, the remains of 10 others were seen floating along a 100-kilometre stretch of the river in the west Canada.

In total, 11 endangered white sturgeon mysteriously died in a short period of time, astonishing biologists, who are trying to save a fish teetering towards extinction.

The species has remained relatively unchanged for 200 million years: toothless summit hunters glide gracefully into handfuls of British Columbia rivers. To navigate the murky waters, sturgeon brushes gently with the brush-like bristles that hang from their nose along the gravel bottom.

The white sturgeon, with its trunk covered with five distinct bony plates called scutes, looks every inch a prehistoric fish. The largest record ever recorded reached 20 feet and another, believed to be 104 years old, weighed nearly 1,800 pounds.

Nyshaku River
Nishako River, where the number of sturgeon has decreased from 5,000 to 500 in the last century. Photography: Fernando Lisse / Alami

“When you see a huge head emerging through the murky waters and the eyes look at you, it’s amazing to see this majestic animal alive,” said Gantner, the British Columbia government’s chief fish biologist. “And you are respected, knowing that most of the fish we see are older than us.”

The rapid succession of deaths took an unexpected emotional toll on Gantner and his colleagues.

“I am very sad. In the past two weeks, I feel like I am suffering from grief. Every time he and his colleagues tenderly move the carcasses of huge fish from the shore to the freezer and onto the autopsy table, he feels the pain of grief.” .”

So far, there are no clear answers. The team found no sign of trauma and no evidence of chemical exposure, illness or death from hunting.

Whatever it was, it affects the larger sturgeon and not other species. It is restricted to a place in time and space. “This gives us some clues,” said Steve McAdam, a biologist at the county’s Department of Lands, Water and Resources. “In a way, it’s easier to rule out a set of things than to control a few things.”

The deaths in Nechako are particularly distressing for McAdam, who studied a similar case of mortality in the lower Fraser River in 1993 and 1994, when the area lost 36 fish in two years.

McAdam said the set of tests that followed that death were inconclusive. The events took place in different ecosystems, separated by hundreds of kilometers, which provides limited evidence for investigators.

Since the team investigating the current episode has a narrow window of time to recover the dead sturgeon before it begins decomposition and destroys valuable evidence, they appealed to the public for help. In an area where fish have deep cultural ties with First Nations and are part of the curriculum in local schools, residents have paid close attention to this phenomenon.

A range of theories have been proposed, including the belief that rising water temperatures are to blame. But McAdam said previous hot summers have not caused similar depletions.

“There is no end to ideas. There are some partial explanations, but we really try to keep an open mind and not get too carried away in one track.”

Sturgeon at the bottom of the river
To navigate the murky waters, sturgeons gently brush the bristly-like arms that hang from their nose along the pebbly bottom. Photo: Minden Pictures / Alamy

Before the mysterious deaths, the white sturgeon, which is listed as a federally endangered species, was already in trouble.

Over the past century, the numbers in the Nechako River have dropped from more than 5,000 to just 500. Soon after the dam was built on the Nechako River in 1957, the species experienced what biologists call a “recruitment failure” – new fish were not being added to the population.

Among this elderly group, which had already lost a whole generation of fish, 11 people died.

Overfishing, drainage projects, and dam building contributed to the collapse. On all the rivers in the province where sturgeon once flourished, dams destroyed their inhabitants. Only the Fraser River, the largest undammed river, has a relatively healthy sturgeon population in the tens of thousands.

British Columbia has worked since 2001 to help the species recover, attracting teams of regional and federal biologists, First Nations groups and industries associated with sturgeon habitat loss, such as hydroelectric dam operators.

Efforts include the use of hatcheries, a “temporary measure” to help populations recover, as well as a far-reaching goal of habitat restoration.

But the sudden death of 11 members of a species already spiraling toward extinction reflects a worldwide trend: sturgeon are becoming the most threatened fish species.

All remaining 26 species of sturgeon is now endangered. They are victims of poaching; In some species, such as the beluga sturgeon, roe is valued as caviar. The habitats they maintained are disappearing.

“It’s a charismatic species and it’s a fish that’s been around for millions of years. So don’t take it seriously when it’s in danger,” McAdam said.

The surprise with which the fish died has puzzled biologists in part because the white sturgeon has been closely studied and monitored for the past three decades, precisely because of their precarious situation.

“And then within a week, this happens. We have a huge new question mark,” Gantner said.

Both Gantner and McAdam hoped that the deaths would lead to a broader end, providing insights for biologists about what could happen — and how a similar outcome might be prevented in the future.

Because the other option – that they have already reached a tipping point – is too bleak to contemplate.

“We’ve never really experienced their complete eradication and seeing how important sturgeon is to the ecosystem,” McAdam said. “And personally, I don’t think we’d ever want to.”

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