Atlantic salmon is one of Maine's true hard-luck species.

Rivers that once filled with tens of thousands of the majestic fish each summer have seen the numbers steadily decline to, in some cases, 10 or 20 fish. Even the intensive efforts to raise and release young salmon has seemed increasingly futile, with one in several hundred hatchery-raised fish somehow making the two-year-long journey to Greenland and back to spawn in its native river.

"The history of salmon is not a great story here in Maine," said Andrew Goode, director of U.S. programs for the Atlantic Salmon Federation.

But advocates like Goode now have some reasons to keep trying.

Salmon runs have doubled in size this summer, with the numbers of returning fish the highest in at least 20 years, experts say.

More than 2,080 salmon have returned to the Penobscot, Maine's premier salmon river and the focus of intensive conservation efforts. That's a fraction of the historic runs of 100,000 leaping salmon, but it follows several years of runs half that size.

Similar increases are being seen in the major salmon rivers of Atlantic Canada. And, although most of the salmon that return to Maine are bound for the Penobscot these days, other Maine rivers are seeing increases in their remnant populations. In the Kennebec, for example, which once had a run of about 50,000 fish, the number climbed to 20 fish so far this summer from about 15 in recent years.

No one knows for sure what's going on.

"It wasn't predicted by the biologists, and salmon is one of the more studied fish in the world," Goode said. "But what they think is that something in the ocean environment has improved."

Scientists believe that warmer ocean temperatures this year may have helped improve the survival of the fish crossing the North Atlantic. But, while the impact of dams that block salmon from reaching upstream spawning grounds is well known, scientists don't really now why so few young salmon return each summer to give it a try.

They may be getting closer to figuring that out.

American and Canadian scientists now hope the use of acoustic transmitters # essentially tiny EZ Passes like the ones mounted in cars # will help them understand what happens to the fish once they head toward Labrador and Greenland. About 30 of 100 tagged fish released in the Penobscot this summer were picked up by acoustic receivers off the coast of Halifax, the researchers said.

Figuring out what's happening in the ocean is key in the long run, said Patrick Keliher, the state's director of sea-run fisheries and habitat.

"It's cause for celebration when you see runs like this, but we really need to see a change in ocean survival," Keliher said. "We're still very cautiously optimistic. We hope that it's more than a one year blip."

One more piece of good news for Salmon this summer is the effort to remove two dams on the Penobscot and create fish passageway at a third. Backers of that effort said this month they have raised the $25 million needed to buy the dams, potentially reopening 500 miles of historic natural habitat for salmon to spawn naturally.

"A lot of folks have said, 'Well, with all these dams in our big rivers, until we address that there's no hope. And we'll never be able to address that.' " Goode said. "But, I think now people are starting to recognize there could be a different future."

Maybe the salmon's luck is changing.

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