by Stephanie Smith
April 28, 2017
Alewives swim against the current in a tributary of the Chesapeake Bay in Cecil County, Maryland, where thousands of river herring gathered to spawn on April 20, 2017.
River herring—alewives and their close relatives, blueback herring—are anadromous: as adults, they live off the Atlantic coast, but they return to freshwater to spawn. For the most part, river herring return to the same streams in which they were born. Scientists aren’t quite sure how the fish manage this migratory feat, but tend to attribute their homing instincts to a sensitivity to polarized light, magnetic signals and the unique characteristics of the waters where they were born.
As water temperatures warm and days lengthen each spring, river herring are spurred to begin their spawning runs. Years ago, some rivers seemed to turn silver or appeared to flow backwards as millions of river herring migrated upstream. The river herring fishery was once one of the most valuable in the Bay—alewives can be eaten fresh, smoked, salted or pickled, as well as used for pet food, as bait for lobster and snow crab or in fishmeal and fish oil. But habitat loss, harvest pressure and migration-restricting barriers like dams and culverts led to a sharp drop in river herring abundance, resulting in harvest moratoriums in Maryland, Virginia and the Potomac River, as well as other states along the East Coast.
These days, river herring populations continue to struggle, and adults must navigate a maze of obstacles to reach their spawning grounds. Sometimes their long journey ends at a dam or other barrier that blocks their access to upstream habitat. By clearing blocked waterways, or by installing fish ladders and lifts that help fish get over or around larger barriers, managers can help river herring recover. “Last month they were out in the Atlantic Ocean somewhere,” said Jim Thompson, a fisheries biologist with the state of Maryland, as he observed last week’s spawning run. “That’s why it’s really important to build these [fish] ladders or take these dams out to get them over that last little speed bump so they can spawn.”
Learn more about the Chesapeake Bay Program’s work to open the region’s streams to the migration of fish.