Lake sturgeons | These survivors threatened with extinction

First considered harmful, then overexploited, the lake sturgeon is now threatened by dams. Four researchers shed light on this issue and on the solutions to be implemented to better protect this species at risk.

A past overexploitation

Overfishing, poaching and, above all, overexploitation for its caviar: the causes of the decline of sturgeon all over the world are well known. After surviving multiple waves of extinction since the time of the dinosaurs (more than 250 million years ago), more than 85% of all sturgeon species are now globally threatened with extinction . However, one species in particular, the lake sturgeon, seemed to escape the rule so far. This freshwater fish unique to North America lives largely in the St. Lawrence River and in the rivers that serve it. But since 2022, it has been added to the International Union for Conservation of Nature (IUCN) Red List of Endangered Species.

“This new listing of lake sturgeon on the IUCN list is worrying and somewhat disheartening,” sighs Constance O’Connor. According to this director of the Ontario Northern Boreal Program at Wildlife Conservancy of Canada, the species is now threatened mainly because of its historical decline. First considered a pest species by the first settlers, it was then heavily exploited at the end of the 19th century.^e century, especially for its meat: it is estimated that in 1900, more than 1000 tonnes of lake sturgeon were caught in the Great Lakes in just one year. “An overexploitation from which the species has never fully recovered,” says Constance O’Connor.

If its fishing is now strongly supervised and authorized in only a few very specific areas, the lake sturgeon is however confronted with a completely different danger: that of the modification of its habitat by dams.

The dangers of dams for lake sturgeon

“Dams are the greatest threat to the lake sturgeon,” says Yves Paradis, biologist at the Ministry of Forests, Wildlife and Parks.

The spawning grounds are areas where the lake sturgeon reproduces. It can sometimes travel hundreds of kilometers to get there in the spring. But even when it does manage to gain access, dams can still disrupt its life cycle. “The lake sturgeon reproduces on a substrate made of large pebbles and with a relatively rapid flow,” points out Samuel Dufour-Pelletier, director of the Environment and Land office of the Abenakis of Odanak Council. When the eggs hatch, the larvae then drift with the currents until they are mature enough to swim. “So if a dam releases water, or holds too much water during this period, it can not only affect its reproduction, but also the survival rate of eggs, the survival rate of larvae, the feeding of young fish…”, enumerates the researcher.

A fish under the magnifying glass of researchers

Studying the lake sturgeon is however a delicate task, since this fish can live up to more than 100 years, and it reaches its sexual maturity around 20 to 30 years: each action implemented can therefore take several decades before that we can see its real impact (positive or negative) on populations. Researchers can, however, rely on indirect indicators to estimate their population, such as the number of individuals, mature females, eggs or larvae found near a spawning ground. Some solutions have thus begun to be put in place to try to save the lake sturgeon, on a small as well as on a large scale.

Samuel Dufour-Pelletier notably studied a population of lake sturgeon located downstream of a dam, at the level of the Saint-François River. In particular, he noticed that “the more water there was in the river during the spawning period, the more the sturgeons went to the spawning ground. And then you have to try to make as few flow variations as possible during the larval period, which lasts two weeks: you have to maintain a stable flow, neither too weak nor too strong”.

The researcher worked with the managers of the hydroelectric plant to adapt its flow rates and thus avoid disturbing the species in the future during its reproduction period. However, “each spawning ground is a little different, each has different flows”, underlines the researcher. “Ideally, this type of study should be done on each dam, to determine what are the best parameters to maximize the reproductive success of lake sturgeon and apply them to the plant. »

For their part, Yves Paradis and his colleague Simon Bernatchez have set out to identify all the known spawning grounds in the St. Lawrence and in the Ottawa River, in order to better protect them and put in place solutions adapted to each of them. they. “The impact of dams is an important issue for the management and conservation of the species by the Ministry”, emphasizes Simon Bernatchez. “However, there is still work to be done, because the distribution area of ​​the lake sturgeon in Quebec is very large,” he admits.

Act before it’s too late

Constance O’Connor welcomes these initiatives which, for her, are crucial for the survival of the species. In particular, it recommends carrying out this type of study more systematically and on a large scale. “We need to find solutions so that the dams have less impact on lake sturgeons,” she says. “It is important to keep in mind that even if they are not in danger today, they could become. It’s the least threatened sturgeon population right now, but we have to make sure it stays that way. »