Pink salmon have maintained a small population in the Great Lakes for 70 years, but recent growth in their numbers both here and abroad has scientists asking new questions.
In 1956, Canadian fisheries managers wanted to introduce pink salmon to Hudson Bay. To do so, they were raising the fish at a hatchery near Thunder Bay, Ontario, on Lake Superior, before transporting fingerlings.
But on one stocking flight, 21,000 extra pink salmon fingerlings didn’t fit, so they were discarded into a sewer. That sewer emptied into the Current River, which flows into Lake Superior.
Pink salmon have been in the Great Lakes ever since, maintaining low but slowly expanding populations. No one had really been monitoring the species closely.
But when fish biologist Joseph Langan started a new position in Michigan and began asking local resource managers about pink salmon, he got some surprising answers.
“Folks were saying, ‘We haven't thought about them a lot, but, you know, we're seeing a lot more of them all of a sudden.’”
Langan is with the National Oceanic and Atmospheric Administration. He said in parts of Lake Huron and Lake Superior, especially, pink salmon populations have been growing over the last 25 years.
“There's a bunch of elements of pink salmon biology that makes them really good at colonizing new habitats and increasing their abundance really quickly,” said Langan.
Despite that, Langan said, there’s no cause for concern yet about pink salmon in the Great Lakes. Their numbers are still low and they don’t seem to be affecting other species. But that’s not the case in other parts of the world.
“Pink salmon are causing management concerns or challenges right now, in three oceans simultaneously,” said Langan.
In the Pacific – their native habitat – they’re starting to outcompete other salmon and certain marine animals for food. In the Arctic, as waters warm up, they’re expanding their range. And in the Atlantic – where pink salmon are invasive – growing numbers are causing big problems, especially when they run up rivers to spawn.
“You can see big numbers of pink salmon splashing around. You see their dorsal fins sticking out of the water. And when they die, they start to die in August here … then you start to see dead pink salmon around,” said Eva Thorstad, a fish biologist with the Norwegian Institute for Nature Research.
Thorstad said Norway only began monitoring pink salmon in 2017, when anglers noticed a population explosion. By 2023, just six years later, pink salmon numbers had increased 50-fold in Nordic nations.
“It's the big numbers that [worry] us — that they both will outgrow the native fish by sheer numbers, compete with them [and] impact ecosystems when they die in the rivers,” said Thorstad.
So researchers across the world want to know more about pink salmon. That’s where Thorstad and Langan are hoping the Great Lakes can come in: they recently published a paper, along with several other scientists, calling for more research on pink salmon in the lakes.
“It's useful for us as an example to see what might be our future. They have adapted to freshwater life in the Great Lakes,” Thorstad said.
For example, their life cycles here are longer than almost everywhere in the ocean: three years, instead of the typical two. And they’ve survived despite the lakes’ intense seasonal temperature changes.
“They're doing some different things [here] than they are in the ocean that are really important for us to try to nail down, because it changes some of the calculus of what we think might be possible for the species,” Langan said. “My dream is to get more of those lines of communication going to try to do some more of this cross comparison.”
Langan and Thorstad’s paper, which was published at the end of April, aims to get more researchers studying a species that may demand more attention soon.
