As the species continues to struggle to reproduce and re-establish historic populations, there have been considerably fewer Atlantic salmon in the Penobscot River this year.
As of the latest trap count report provided Aug. 23 by the Maine Department of Marine Resources, only 520 salmon have passed through the Milford and Orono dams this year.
That is fewer fish than were counted, as of the same date, in each of the previous four years and represents the fourth lowest total since 2000.
But one down year doesn’t spell disaster for the species.
“There are many factors that might contribute to the lower run this year, the most significant likely being low survival at sea and poor freshwater survival and passage at dams for juveniles in prior years,” said Sean Ledwin, the sea run fisheries and habitat division director for the Department of Marine Resources.
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.
Ledwin said Atlantic salmon returns vary significantly from year to year, especially given the reduced populations that have existed over the last two decades.
Despite the presence of a high-tech fish lift and passage at Brookfield Renewable’s Milford Dam, and the efforts of scientists, Maine’s salmon do not seem able to reproduce here in large numbers.
“We see very low numbers of fish returning that are from natural spawning or were stocked above hydropower dams, with most returns coming from salmon that were stocked as smolts below the Milford Dam,” Ledwin said.
Ledwin said it is possible more salmon will appear prior in the Penobscot before the end of the year, but it’s unlikely. Given the timing of the historic runs and warm water temperatures, the numbers likely won’t change significantly, he said.
Atlantic salmon, once targeted as part of an important sport fishery in Maine, have been reduced to a distant memory, or a glimmer of hope for the future.
Atlantic salmon in the Penobscot and Kennebec Rivers are hampered by hydropower dams, which reduce their ability to reach spawning grounds.
“We get very few ‘repeat spawners,’ which is probably due to the impacts of delays and passage at the dams and poor ocean survival,” Ledwin said.
He cited a recent University of Maine study that looked at the impact of passage delays at Milford and at the Lockwood Dam on the Kennebec in Augusta. The work found that fish can take weeks to even find the fishways.
“[Those dynamics] can result in significant numbers of fish dying before spawning and [a] loss of ‘repeat spawners,’ which is concerning,” Ledwin said.
If the numbers continue trending as they have been, this year’s Atlantic salmon return on the Penobscot is likely to wind up as the lowest since 507 fish were counted in 2016.
Salmon numbered 1,196 on the Penobscot in 2019, so this year’s return may also break a two-year streak of at least 1,110 fish.
On the Kennebec, only 15 adult salmon — those that have spent at least two winters at sea — and eight grilse have been counted at the Lockwood Dam.
It is likely to wind up as the lowest return at that dam since 2018 (11 fish), although the high tally since 2010 is only 64.
For other species, there is better news. Ledwin said marine resources biologists are encouraged by the continued healthy runs of river herring, also known as alewives, coming into the Penobscot. Counts place the 2021 return as numbering more than 1.7 million fish, which is down slightly from the estimated 2 million alewives counted each of the last two years.
The high tally for river herring on the Penobscot was 2,175,687 in 2018.
“Another study by the University of Maine showed that restored runs of river herring were benefiting salmon in the Penobscot by reducing predation pressure by seals as river herring are much more abundant that salmon and a great seal snack,” Ledwin said.
He also said new alewife runs taking shape in the Mattawamkeag River watershed may more than double the Penobscot River runs in the next few years. That would be aided by the installation of a fish passage at a dam in Danforth.