WASHINGTON COUNTY, Me. – Ernie Atkinson waded up Old Stream on a warm fall afternoon, peering through polarized sunglasses to scan the streambed. Before long, he pointed out a place where the bottom looked different.
“You can see how the gravel is a lot cleaner right here–it kind of shines,” said Mr. Atkinson, a fishery biologist with the Maine Department of Marine Resources. “O.K., we’ve got one, two, four redds right here.”
Redds are places where spawning salmon use their tails to dig holes in the gravel, deposit their eggs and bury them. For much of the past 20 years, counting redds here was a grim task; by 2000, the population of Atlantic salmon here had fallen so low that they were declared an endangered species in eight Maine rivers.
Since then, despite millions of dollars in conservation spending, the runs improved only gradually.
Until this year, that is. More than 3,100 salmon returned to the Penobscot River, the most since 1986, and nearly 200 ascended the Narraguagus River, up from the low two digits just a decade ago.
“We’re pretty stoked, you could say,” Mr. Atkinson said.
But while this year’s comeback has been a welcome surprise for conservationists and environmental officials, scientists caution that the long-term picture is still cloudy — and that much could depend on factors far from Maine.
Atlantic salmon hatch in the rivers in spring, mature for two or three years, then swim to sea. Some return to the rivers after just one year, but most spend two years at sea, eventually gathering with salmon from all across the Atlantic in the waters west of Greenland.
John F. Kocik, a research biologist with the National Oceanic and Atmospheric Administration’s fisheries service, says that in recent years salmon have been faring poorly during their time at sea. Waters have been too warm for salmon in some places and too cold in others, partly influenced by periodic weather patterns known as the North Atlantic oscillation and the Atlantic multidecadal oscillation. “Both of those seem to be coming into play,” Dr. Kocik said.
He added that there was more to be learned. “There are also, we believe, some more complex food-chain issues going on that we are trying to understand,” he said.
Dr. Kocik noted that salmon from eastern Canada also seemed to be making a comeback this year. “The one thing it definitely shows is how connected all of the salmon — not only in New England, but in Atlantic Canada — are,” he said, “because they are having some pretty good returns this year as well.”
Ever since the Maine salmon were listed under the federal Endangered Species Act, recovery efforts have been in high gear. Biologists have studied salmon habitat and migration routes, and stocked millions of juvenile salmon. Conservation groups protected lands along hundreds of miles of salmon rivers and fought for tighter regulations on salmon farms. In 2009, federal regulators expanded the listing to include salmon habitats in Maine’s largest rivers — including the Penobscot, where a dam-removal project will soon allow salmon better access to miles of spawning habitat.
Andrew Goode, a vice president at the Atlantic Salmon Federation, a conservation group, said that the population had been gradually improving since it bottomed out around 2000, but that “this year was definitely off the charts.”
But he added that this year might be an outlier, and said he was concerned that the increase was already prompting calls to reopen the commercial salmon fishery in Greenland, which has been closed in recent years.
“It’s easy to say something has improved in the marine environment, but we want to know what’s improving,” he said. “I think it’s going to take the hard-core science community several years to tease out what’s going on.”
Kevin Friedland, a marine scientist with NOAA, said that although Maine salmon clearly got a reprieve this year, climate projections mean the long-term prognosis is not good. “Warming in recent decades has not been good for salmon,” he said. “Further warming, we don’t know what that will do to salmon.”
Dr. Friedland said one factor that contributed to Maine salmon’s decline is new challenges in their first weeks at sea. “In North America, we believe the fish are entering a warmer set of ocean conditions,” he said, “and with it is coming a more aggressive predator field.” He said tailwinds that help the migrating salmon move quickly offshore can improve survival.
On Old Stream, Mr. Atkinson tallied eight redds in one short reach. Standing on the bank, he briefed a biology class from the University of Maine at Machias. He said his colleagues had found more redds downstream, and this small tributary to the Machias River is loaded with salmon.
“As of last Friday, we were up to 50 redds, and they were still digging,” he said. “It’s a really good year.”