MONTPELIER, Vt. — The federal government is ending its conservation effort to restore Atlantic salmon in the Connecticut River basin because the nearly half-century old program that has stocked about 100 million small fish in tributaries throughout western New England is not working well enough to justify the continued cost, an official said Wednesday.

The U.S. Fish and Wildlife Service also is beginning a three-year evaluation of a similar program in the Merrimack River basin in Massachusetts and New Hampshire, which could lead to the end of its participation in Atlantic salmon restoration programs there as well, said Fish and Wildlife Regional Assistant Director for Fisheries Bill Archambault.

The only bright spot for Atlantic salmon in the northeastern United States is in Maine where salmon, which were once common throughout the region, continue to return in relatively large numbers to the Penobscot River basin after growing to adulthood in the North Atlantic and returning to the small rivers and streams to spawn, he said.

“I think I speak for most of the biologists for the U.S. Fish and Wildlife Service in that we would very much like to see Atlantic salmon restored to the Connecticut River,” Archambault said. “These are by far the most high-profile, majestic fish of the Connecticut River.”

In 2010 Fish and Wildlife stocked around 6 million tiny fry and 75,000 to 90,000 larger salmon smolts throughout the Connecticut River estuary at a cost of about $2 million. This spring about 50 adult salmon returned to the Connecticut to spawn in the tributaries where they were released, Archambault said.

To build a self-sustaining population would require the return of at least 1,000 fish a year, Archambault said.

“The fact is there was a lot of money thrown at this for a long time. And the fact that the agency with the statutory responsibility for recovering these fish has admitted failure is significant,” said Chris Wood, the president of Trout Unlimited the national group that works to promote the health of cold-water fish. “The larger perspective is that trout and salmon are the ultimate indicators of the health of the land because every single thing that we do on the land is indicated by the health of the rivers that surround us.”

When Europeans first arrived in what is now New England almost 400 years ago, hundreds of thousands of Atlantic salmon swam up the Connecticut River every year almost to the Canadian border. But the stocks were wiped out around 1800 after the construction of dams kept the fish from making it upstream.

In 1967 Vermont, New Hampshire, Massachusetts and Connecticut got together with the U.S. Fish and Wildlife Service and started working to restore Atlantic salmon to the Connecticut River basin.

If scientists learn more from successful Atlantic salmon programs elsewhere the Connecticut River program could be brought back. “But the science right now just doesn’t justify continued effort from the Fish and Wildlife Service standpoint. I totally agree and am very comfortable with the science that allowed us to redirect,” Archambault said.

Wood said there were too many obstacles in the Connecticut River to successful Atlantic salmon restoration, including dams that block fish access to the tributaries where they breed. He pointed to Maine’s Penobscot River, where conservation efforts are removing dams that block fish access to their breeding grounds, opening up more than 1,000 miles of tributaries.

Archambault called the Penobscot “the last great hope for salmon in the lower 48.”

The Fish and Wildlife decision, announced Tuesday at a meeting in Hadley, Mass., ends the federal participation in the Atlantic salmon restoration. Connecticut and Massachusetts could choose to continue their own programs, Archambault said.

The fish released into the tributaries of Vermont, New Hampshire, Massachusetts and Connecticut live there until they are two years old and then swim downstream into the Connecticut River and then the Atlantic Ocean. They will spend their adult lives in the North Atlantic before returning to the streams where they were released to breed.

Enough of the fish are making it into the Atlantic Ocean. Scientists don’t know why so few fish and able to return from the Atlantic.

The Fish and Wildlife Service is helping to run a similar program in the Merrimack River. Scientists are doing a three-year evaluation of the program there as well. If the rates of return continue to remain low the federal participation in that program will likely end as well.

Despite of the failure of the Atlantic salmon program to restore a breeding population, it had other benefits, including an improved habitat, the removal of some dams and installation of fish ladders that have benefited other species, Archambault said.

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