For the first time in more than a century, scientists have found wild-born Atlantic salmon in a Lake Ontario tributary that once teemed with the fish, suggesting that the native species is recovering after many years of reproductive failure.

Jim Johnson, a biologist with the U.S. Geological Survey, said Wednesday that 41 yearling wild Atlantic salmon were collected this summer in the Salmon River at the eastern end of the lake in New York. He attributes the increase to changes in the lake's food chain.

Atlantic salmon were once abundant in Lake Ontario and its tributaries, with reports from the 1800s of fishermen catching thousands of 15- to 20-pound fish per night from the Salmon River. By the turn of the century, overfishing, dams, deforestation and pollution had wiped out the population.

State and federal natural resources agencies in the U.S. and Canada, as well as wildlife and sportsmen's groups, have been working to restore the Atlantic salmon to Lake Ontario. New York state's Department of Environmental Conservation releases 30,000 Atlantic salmon annually from a hatchery in the Adirondack Mountains in upstate New York, but few of the fish survive to return to the Salmon River as spawning adults.

The introduction of the invasive alewife more than 50 years ago is cited as a major cause for the decline of wild salmon. Alewives contain thiaminase, an enzyme that destroys the critical vitamin thiamine in salmon that eat the small fish. When the salmon reproduce, their hatchlings die of thiamine deficiency.

Recent declines in alewife populations in Lake Ontario, coinciding with an increase in native prey fish, may be boosting Atlantic salmon populations, Johnson said.

"This provides some hope that we can get natural reproduction of Atlantic salmon despite the thiaminase issue," said Dan Bishop, a regional fishery manager for the New York State Department of Environmental Conservation. "Our thinking was that the reproductive impairment would be very difficult to overcome."

Johnson said the young wild salmon discovered this summer - recognized as wild because they are smaller and younger than stocked fish - were the progeny of hatchery fish that had survived to adulthood and successfully reproduced.

"This is great news," said Marion Daniels, management biologist with the Ontario Ministry of Natural Resources in Toronto, which launched the Lake Ontario Atlantic Salmon Restoration Program in 2006 along with more than 50 partners.

"We have not confirmed wild reproduction on our side yet, but in the last couple of years we've had adult salmon returning to the Credit River," Daniels said. The restoration program involves stocking streams with hundreds of thousands of hatchery-raised salmon, improving stream habitat, and removing barriers to spawning fish.

Lake trout, as well as chinook, steelhead and coho salmon, which aren't native to New York, are released by hatcheries and reproduce successfully in New York to a limited degree.

Johnson said those species are less susceptible to the thiamine depletion because they migrate to the ocean, while Atlantic salmon grow up in Lake Ontario.