Dams and acid rain are the major impediments to the recovery of Maine’s wild Atlantic salmon population, and saving the fish could cost tens of millions of dollars, according to a report released Tuesday afternoon by the National Research Council.

The long-awaited report was written over the past two years by a 13-member committee of scientists from across the nation who had been charged with investigating why Maine’s wild salmon are declining, and what actions the state might take to “rehabilitate” its fish population.

The Atlantic salmon’s situation is dire, the committee said. In the early 1800s, millions of fish spawned in Northeastern rivers each year. Today, wild Atlantic salmon are found primarily in Maine, and only 871 salmon returned to the state’s 17 rivers in 2002.

No one action alone will save the salmon, the committee said, describing a complex list of contributing causes over hundreds of years, ranging from historic overfishing to industrial pollution and global warming.

Atlantic salmon have one of the most complicated life cycles in the animal kingdom, hatching in rivers, then traveling through estuaries to the open Atlantic and back again – often several times within a single fish’s lifetime. Nearly all of the world’s environmental problems have the potential to affect salmon, with many so large in scale that the state of Maine alone can have little effect.

“We are faced with a problem of ecosystem management, where management choices are shrouded in uncertainty,” wrote committee chairman Michael Clegg of the University of California in the report’s introduction. “This challenge has humbled us.”

Dam removal should be the state’s first priority, the committee said, estimating an annual cost between $300,000 and $15 million to remove three to five dams per year.

Not only do dams block salmon from returning to their historic spawning grounds, they can alter rivers by raising water levels and changing its speed, chemistry and temperature, the report said.

The committee lauded a continuing effort to remove two dams and improve fish passage facilities on the Penobscot River. Working together on the project is a coalition of environmental groups, the state, the Penobscot Nation and PPL Corp., owner of the hydroelectric dams.

Home to 90 percent of the state’s returning salmon, the river is “by far the greatest natural environmental asset for salmon in Maine,” and should be a focus for the salmon recovery effort, the report said.

Maine has hundreds of dams, many of which are no longer crucial to the state’s electricity supply. Dam removals should be prioritized based on the amount of habitat that could be reclaimed, the committee said.

As a second priority, the committee recommended that the state look at ways to address the acidification of Maine’s rivers. When rain, snow and even dew fall through polluted air, lakes and rivers become acidic.

High acid levels can kill eggs and hatchlings. And recent research suggests that even a slight change in the water chemistry can interfere with a salmon’s natural ability to adapt when it travels between fresh water and salt water.

The committee recommends that the state work to reduce the acidity of salmon rivers by applying lime as a “quick and effective remedy.”

A liming program would require an initial investment of about $100,000 per stream, then $50,000 to $100,000 in total per year to maintain the right chemical balance, the report said.

Longer-term recommendations include limiting the introduction of hatchery fish into salmon rivers, beefing up protections against the escape of aquaculture fish, and continuing limits on fishing.

Most of the committee’s recommendations are already “on the radar screen,” Pat Keliher, executive director of the Maine Atlantic Salmon Commission, said Thursday.

Several dam removal projects are under way, and should be accomplished with a minimum of controversy, so long as “all the parties are at the table,” Keliher said.

A liming experiment is planned for the Dennys River, should legislators this session approve a bill adjusting Department of Environmental Protection rules.

However, any application of this report faces the same challenge as its countless predecessors – funding. Even with the $1.2 million Maine expects from the National Oceanic and Atmospheric Administration next year, saving Atlantic salmon is going to be a challenge, requiring cooperation among agencies and nonprofit groups.

“As much as we would love to, the state can’t just go ahead and do everything. This stuff is expensive … it’s going to cost time and money,” Keliher said.

Copies of the full report are available online at http://www.nap.edu or by contacting the National Academies Press at (202) 334-3313 or 1-800-624-6242.