An Atlantic salmon makes its way to a holding tank at the Milford Dam fishway at Brookfield Energy in Milford in June 2015. Credit: Ashley L. Conti / BDN

Only 561 Atlantic salmon were counted in the Penobscot River last year, marking the lowest returns since 2016, when 503 fish made their way through to Milford and Orono.

The final numbers provided by the Maine Department of Marine Resources come on the heels of a robust influx of 1,439 Atlantic salmon one year earlier that marked the highest return since 2011.

“The reasons for the low runs are likely low survival of fish at sea, the impacts of drought during their time in the river and impacts of impoundments and direct mortality at hydropower projects as the fish migrate from the rivers to the sea,” said Sean Ledwin, DMR’s Sea Run Fisheries and Habitat Director.

These are among the obstacles scientists continue to monitor as they try to reestablish a self-sustaining Atlantic salmon population in Maine’s rivers. And despite the 61 percent reduction in returns to the Penobscot River last year, experts are not alarmed.

“While this year’s low returns continue a concerning trend of low abundance, they are not that far out of line with returns in the last 10 years, which have averaged 732 fish per year,” Ledwin said.

The 2021 total was the fourth lowest since 2000, but Ledwin previously explained that the reduced populations of Atlantic salmon over the last two decades means returns to Maine rivers often vary widely from year to year.

Maine is home to the only native Atlantic salmon populations in the U.S., where the fish have been protected under the federal Endangered Species Act since 2000.

Atlantic salmon were once a prized catch for sport anglers, who visited the Penobscot in large numbers.

Atlantic salmon in the Penobscot and Kennebec rivers are hampered by hydropower dams, which eliminate or reduce their ability to reach spawning grounds.

Ledwin said DMR staff reported the salmon that did return were in similar physical shape to those that made it back in previous years.

“Salmon runs continue to be disappointing as we are still far away from being able to downlist the species and get self-sustaining runs that could support a fishery,” Ledwin said.

DMR biologists continue to work alongside Brookfield Renewable, which operates most of Maine’s hydroelectric river dams, and other conservation groups such as the Atlantic Salmon Federation and Trout Unlimited in search of ways to make it more practical for Atlantic salmon to make it into the rivers, past dams and back to their traditional spawning grounds.

A major key is giving Atlantic salmon a means to bypass hydro dams and other manmade obstacles. Only 23 salmon were counted at Brookfield’s Lockwood Dam in 2021, while 21 were tallied on the Narraguagus River in Cherryfield, according to DMR trap counts.

“We have a lot more control of the freshwater environment than when fish are at sea,” Ledwin said, “and therefore we are prioritizing improving upstream and downstream fish passage at dams and increasing the numbers of fish in high quality, productive habitats in tributaries of the Penobscot such as the Piscataquis and East Branch.”

Pete graduated from Bangor High School in 1980 and earned a B.S. in Journalism (Advertising) from the University of Maine in 1986. He grew up fishing at his family's camp on Sebago Lake but didn't take...