Introduced Salmon Could Be Hurting Native Fish

By Lucas Habib
SPARK Program
and Lori Bona Hunt

Pacific salmon that have been stocked in the Great Lakes could be preventing depleted populations of native Atlantic salmon from recovering, say researchers.

Findings of a study conducted by Profs. David Noakes and Bill Beamish, Zoology, and Robert Scott of the University of Western Ontario reveal that introduced species are disrupting the social hierarchies set up by native Atlantic salmon.

The researchers examined the behaviour, feeding and spawning habits of both native and introduced salmonids - including chinook salmon, coho salmon and rainbow trout - in the Great Lakes. They found that the exotic species, especially chinooks, show little regard for Atlantic salmon, and physically and aggressively try to displace them if they're in the way. As a result, in the presence of Pacific fish, the Atlantics change their behaviour.

"They are getting pushed around by the exotics," says Noakes, "so they spend more time being aggressive and bumping each other around than they do feeding, digging nests and reproducing."

By the end of the 19th century, Atlantic salmon had been depleted in the Great Lakes by overfishing and habitat loss. Since the 1960s, Pacific salmon have been stocked in Lake Ontario for sport fishing.

"There have also been many attempts to restore Atlantic salmon, and all have been met with little or no success," says Scott. "We're trying to determine if the Pacific salmonids are inhibiting the restoration of these native fish."

The researchers examined the interactions between Atlantic and Pacific salmon on spawning grounds in a creek near Oshawa that flows into Lake Ontario. The creek was divided into sections, with Atlantic salmon in all the sections and Pacific chinook salmon in only half. This way, they could observe how the Atlantic salmon behaved both alone and with Pacific salmon. They also studied their survival and spawning habits.

"Then we will put the pieces of the pie back together and see at what level the fish are successful and, if not, where the weak link is in the chain," says Noakes.

Ultimately, the researchers hope to create a sophisticated model that can be used to make predictions about the survival of salmon on the west and east coasts.

Noakes adds that it's important to keep in mind that Atlantic salmon are "the villains or the heroes," depending on which part of the country you're in.

"On the west coast, Atlantics are the introduced exotics and are wiping out the natives, so they are considered the 'ultimate evil.'"

The research is a collaborative project involving several universities and is sponsored by the Natural Sciences and Engineering Research Council, the Ontario Ministry of Natural Resources and the Department of Fisheries and Oceans.