Alewife Migration Maine | Conservation Photography Gallery
Alewife Migration & Dam Removal
Alewives (a species of river herring) are anadromous: adults live in the ocean but each spring swim upstream into rivers, lakes, and ponds to spawn (typically late April–June). After spawning their offspring grow in freshwater for months before heading back to sea; adults often repeat this cycle multiple years. They’re key forage fish and move huge amounts of marine nutrients into freshwater ecosystems, benefiting birds, mammals, freshwater fishes, and even mussels.
Historic decline and the role of dams Through the 19th and 20th centuries, many coastal dams and impassable culverts in new England blocked access to historic spawning habitat; harvest pressure and ocean factors also reduced runs. Large reaches that once supported tens of millions of fish were cut off, producing severe local declines. Removing or bypassing dams in Maine and New Hampshire has repeatedly produced large, often rapid increases in alewife and other river-herring returns: The Penobscot River restoration (removal of Great Works in 2012 and Veazie in 2013 plus a bypass at Howland) reopened nearly 2,000 miles of habitat and coincided with millions of migratory fish returning — reports cite multi-million returns in recent years tied to that project.
Shown here the successful population increase of fish returning to the Exeter River after the Great Dam was removed in 2016. I also look at Mill Brook and the healthy population of migrating fish returning each year to Highland Lake in Maine to spawn.