In the Midcoast, the annual alewife run is a sure sign that spring is really here – or is it better to say that spring signals the arrival of alewives?
For those who harvest the two species of river herring that choke coastal rivers and streams by the thousands every year as they migrate inland to spawn, timing the alewives’ movement right is crucial to logging accurate data and maximizing harvests.
Factors like water temperature and stream flows affect alewife movement, which can happen any time between April and early June. For Jeff Pierce, president of the Alewife Harvesters of Maine, predicting the alewife run is as simple as knowing nature’s cues.
“Go down to the stream, open your eyes, and look around,” he said.
Pierce, a Dresden resident, has learned what to look for over more than two decades of harvesting alewives and said his predictions based on those clues haven’t led him astray in 22 years.
Pierce begins his season by preparing his nets when the crocuses are beginning to bloom. Then, he looks to the trees for his next clue.
“I always say to look at the buds on the trees. The alewives will run when the buds are as big as a mouse’s ear,” he said on Monday, April 21, the day after the alewives had begun to migrate in Dresden.
Other signs include the presence of birds of prey upriver, algae beginning to grow on river rocks, and a congregation of seals and cormorants at the river’s mouth, Pierce said.
“Nature doesn’t go where there’s no food,” he said.
Abden Simmons, a Waldoboro Select Board member who led the effort to install a fish counter in the Medomak River, said he looks for the fish themselves to time their arrival. A few fish begin appearing in the lower river before the run begins in earnest, he said, and he will sometimes see these early arrivals while fishing for eels.
State scientists who study alewives are also interested in the timing of the annual alewife run. The Maine Department of Marine Resources tracks the arrival at various monitoring locations state-wide, said Michael Brown, a state marine resource scientist.
There are two major clues the DMR assesses to predict alewife migration, Brown said: water temperature and stream flow rate.
“As water temperatures approach the low 50s, alewives start to migrate into spawning habitats,” he said.
This, he added, is provided their streams aren’t flowing too aggressively. If currents are moving too quickly, the fish will drop down into the bay to wait for better conditions. Pierce echoed this wisdom, noting that an unfavorable wind or cold tide can also prevent alewives from running upstream.
Brown noted many species across the ecosystem rely on the same temperature and light cues to time their yearly behavior and growth cycles. This means that during a year when, for example, alewives are running early, other natural clues – like the growth of buds on trees – are likely to be keeping pace.
The DMR works with commercial harvesters, educational institutions, land trusts, and fish counting efforts – like those in Waldoboro and at Damariscotta Mills – to collect yearly data on run timing and fish populations, according to Brown.
“These data are all used to look at shifts in population dynamics and for significant changes in behavior that may need to be accounted for in our management programs,” he said.
In Waldoboro, the addition of an electronic fish counter has greatly increased the town’s knowledge of its fishery, Simmons said. In the first year the fish counter was used, the town about doubled their estimation of the fish population in the Medomak. In 2024, the town counted 265,000 alewives migrating through the river.
“It was a huge eye-opener for the electronic counter to be in place 24/7,” he said.
Simmons hopes to see alewife habitat expanded upstream by removing obstructions farther north. Ultimately, this will help restore the ability to harvest alewives locally, he said. The population of alewives in the Medomak is not currently estimated to be high enough to support fishing.
“It all revolves around habitat, if we’ve got the habitat to support all those fish,” he said.
Restoring alewife populations also benefits the greater ecosystem, Simmons said.
“Alewives feed on phosphorus, so they clean up lakes and make the water quality a lot better,” he said.
Brown, Pierce, and Simmons noted that the timing of alewife runs can vary widely from location to location and year to year, fluctuating with year-to-year weather patterns.
Milder winters and warming waters seem to be contributing to shifts to slightly earlier runs at some locations, Brown said. Some locations in the Midcoast, in particular, have observed “very early start times,” with fish running as soon as early April.
“During the past decade Maine has experienced some very mild winter conditions. Late ice-up and early ice-out of lakes and ponds allows waters to warm earlier than normal in the spring,” contributing to earlier than typical alewife migration, he said.
However, any conclusions about long-term shifts in alewife behavior will require data collection over “a long period of time,” he said. The DMR will continue to gather data in collaboration with harvesters and scientists statewide, he said.
