Eastern-flowing ocean currents and fish-rich seas off southern Patagonia have likely allowed the salmon to spread to Atlantic waters, said study team member Miguel Pascual of the Centro Nacional Patagónico in Chubut, Argentina.
"Salmon can migrate long distances in the ocean, and they can be caught almost anywhere in the Southern Ocean," Pascual said, referring to the waters that surround Antarctica.
One salmon was recorded as far north as Uruguay, he added.
The cooler waters of southern Argentina make the region most vulnerable to invasion, Pascual said, and the area's trout rivers are likely targets for the invasive salmon.
While anglers have yet to hook any of the salmon, "[the fish] are creating a stir among sport fishermen who regard them as an addition to other valuable fisheries for steelhead and sea trout," Pascual said.
But the impact of these sea-feeding fish on the marine environment may prove severe, according to the latest research carried out by Pascual and his colleagues.
A new study, yet to be published, found that 96 percent of the chinook salmon's diet in Patagonian seas is made up of sprats, small herring-like fish that are key prey for Magellanic penguins, a species classified as "near threatened" by the World Conservation Union.
(See a photo of Magellanic penguins.)
While the number of chinook salmon in the region isn't yet known, models indicate that a "medium-size population" could match the food consumption of the entire penguin population of southern Patagonia, Pascual said.
Chile's Escaping Fish
The team also warns that the number of salmon finding their way to Argentina is likely to grow "as Chile moves forward to become the largest [farmed] salmon producer in the world."
Staniford, of the Pure Salmon Campaign, said salmon escapes from Chilean farms are spiraling out of control.
Millions of fish reportedly escaped in a single incident last year, when an earthquake triggered a mini-tsunami that hit salmon farms in Chile's Aysen region, Staniford noted.
In addition to competing with penguins and sea mammals for prey, escapees can spread disease and parasitic sea lice that affect wild fish, Staniford added.
(Read related story: "Sea Lice From Fish Farms May Wipe Out Wild Salmon" [December 13, 2007].)
"Escaped farm salmon, unlike domesticated cows or sheep, can swim vast distances and are mobile pollutants," he said.
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