World Fish Migration Day: What River Herring Teach Us About Connected Ecosystems

Migratory fish connect ecosystems in ways few species can. From ocean depths to inland rivers, their journeys link habitats, fuel food webs, and sustain both wildlife and communities.

World Fish Migration Day, celebrated every two years, is a global call to recognize these connections and take action to protect free-flowing rivers. Around the world, people come together to learn, imagine, and act for fish and the waters they depend on.

Each spring in the Gulf of Maine, river herring begin one of these remarkable migrations. After years in the ocean, alewives and blueback herring return to the freshwater streams and ponds where they were born, moving upstream to spawn before heading back to sea. This ancient cycle makes them a vital link between marine and freshwater ecosystems.

River herring are often called “the fish that feeds them all.” They are a critical food source for birds, marine mammals, and commercially important fish like cod and haddock. Their presence helps move nutrients across ecosystems and supports the health of entire coastal food webs.

But this migration has become increasingly difficult. Dams, culverts, pollution, and climate change have reduced river herring populations to a fraction of their historic levels. For centuries, barriers have blocked access to spawning habitat, disrupting a life cycle that depends on connected rivers.

There is progress. Dam removal, fishway construction, improved water quality, and limits on harvest are helping river herring runs begin to recover in parts of the Gulf of Maine.

Manomet Conservation Sciences is part of that effort. Through the Gulf of Maine River Herring Network, Manomet works with local harvesters, agencies, and community groups to restore these migrations stream by stream, pond by pond. By tracking river herring runs and supporting community-driven stewardship, this work helps rebuild populations while strengthening coastal ecosystems in a warming climate.

On this World Fish Migration Day, river herring remind us what’s possible when rivers flow freely and what’s at stake when they don’t.