Spring is in full swing here in Maine, which means alewives are on their way from the ocean into our rivers, lakes and streams. From mid-May to mid-June, millions of these small, silver forage fish navigate rivers throughout the state as they make their seasonal migrations to their freshwater spawning grounds. Along the way, they serve as prey for a wide range of species – from osprey, eagles and herons to striped bass, trout, otters, minks and more. In areas where there are sustainable runs, alewives are also commercially harvested as a favored bait for the spring lobster fishery.

While alewives have gained increasing attention in recent years (largely due to their incredible recovery after dams, pollution and overfishing depleted their populations), our collective efforts to restore them have had important benefits for many other sea-run fish species.

Alewives and blueback herring, collectively referred to as river herring, are part of Maine’s “diadromous dozen,” which also includes American eel, Atlantic salmon, Atlantic and shortnose sturgeon, sea-run brook trout, striped bass, American shad, rainbow smelt, sea lamprey and tomcod. Diadromous species spawn in freshwater, then migrate to the sea to live out most of their adult lives. (The American eel is the only one that does this in reverse, coming to Maine’s rivers as juvenile eels called elvers after spawning in the Sargasso Sea.)

While diadromous fish once freely traversed between Maine’s bays, rivers and streams, they now encounter barriers to their migrations in the form of dams and road crossings that block access to their upstream habitats. Much of our work at the Downeast Salmon Federation – and our many Nature Connects collaborators – is concerned with removing or repairing these fish passage barriers.

Following the removal of the Edwards and Fort Halifax dams in Augusta and Winslow in 1999, millions of alewives now return each year to the Kennebec River, which currently has the largest alewife run in the U.S. On the Skutik-St. Croix River, where a series of dams has blocked fish passage since the 1880s, decades of restoration efforts paid off when, just last year, 840,000 alewives were counted at the Milltown Dam in Calais. That was the final fish count at that dam, as shortly thereafter, work began to decommission and remove it from the river. With continued improvements at other dams along the Skutik-St. Croix, an estimated 20 million fish could return there each year.

These efforts to restore fish passageways benefit Maine’s river ecosystems and the many other fish that depend on them, including our most imperiled sea-run species: Atlantic salmon. In the spring, salmon transform into smolts with their signature silver color and begin to leave our rivers. Alewives provide food for the salmon, but perhaps more importantly, when the waters are filled with alewives for other predators to eat, salmon have a better chance of surviving their arduous journey to the sea.

This spring, you can join the ongoing efforts to conserve river ecosystems and support the resilience of nature. Saturday, May 25, is World Fish Migration Day, when people around the planet gather to celebrate the importance of migratory fish. There are amazing events happening across the state, including the Pennamaquan Alewife Festival in Pembroke, which will have smoked fish, live music and talks by fisheries biologists along the banks of the Pennamaquan River, where repairs to a fish ladder in 2020 have helped restore alewife populations. To experience alewife runs for yourself, check out the Maine Rivers’ Alewife Trail Map, where you’ll find nearly 20 sites to observe an astonishing display of nature, while learning more about conservation efforts to restore this humble, beloved fish.

Stream by stream, river by river, we are waking up to the benefits of having healthy waters full of fish. Each improvement we make to fix the environmental problems we’ve caused is another step closer to restoring all of Maine’s diadromous dozen.

Nature Connects is a monthly column featuring conservation stories from people and organizations across Maine. To learn more or suggest story ideas, email reply@mcht.org.