The Alewife (Alosa pseudoharengus) or River Herring, is one of the most important anadromous fish in the coastal ecosystem. An anadromous fish is a fish that spends most of its life out in the ocean, but swims into freshwater bodies to spawn. These fish school by the thousands in mid-spring, coming from all directions searching for their spawning grounds. They make their way up turbulent, swelling spring rivers in search of calmer lakes and ponds to drop their eggs. This mass migration of fish into coastal fresh water bodies brings a huge nutrient influx to the local ecosytem. This food source is important for birds like eagles, osprey, herons, and gulls. Many mammals also take advantage of this influx, as these fish are easy pickings when they come to a bottleneck in a river or stream. Striped bass will also follow these fish up river and prey upon them as well.
This adapted anadromous behavior has been beneficial to the species for millenia, but it ran into problems when people began constructing mill dams along rivers throughout northeast coastline. Dams constructed along rivers to power sawmills had the unintended consequence of blocking millions of alewives access to their spawning grounds. Alewife populations quickly plumetted. Over the past 100 years, these mill dams have become obsolete, and many of them have been descontructed, restoring alewives access to spawning areas. These fish have very high fecundity, one female capable of laying 70,000 eggs in a season, and thus are quick to recover when given the opportunity. To learn more about the push for alewife restoration, counting efforts, and dam removal, visit the Herring Alliance.