A school of alewife spawn in the calm shallows where Deer Creek meets the Susquehanna River in Susquehanna State Park in Havre de Grace, Maryland, on April 16, 2015.
Alewife (Alosa pseudoharengus) and their close relative blueback herring (Alosa aestivalis) are collectively known as "river herring." The two can be difficult to distinguish from one another—both are thin, silver-sided fish, each with a single dark spot located behind its head. Alewife, however, can be distinguished by their bronze-green backs, whereas the aptly named blueback has a blue-colored back.
River herring are anadromous: they spend their adult lives at sea, returning to freshwater areas only to spawn in the spring. The small fish serve as important prey for larger predators like striped bass and bluefish. They also once served as one of the largest fisheries in the Chesapeake Bay; in 1931, over 25 million pounds of river herring were harvested from the estuary.
But the destruction of spawning habitat, the constructions of dams restricting migration and increased fishing pressure led to a major decline in river herring abundance. In 2006, commercial catch of river herring for the entire Atlantic coast totaled just 823,000 pounds. By 2012, Maryland, Virginia and the Potomac River had harvest moratoriums for river herring in place, as did many other states along the East Coast.
To restore herring to the Chesapeake Bay, experts like the Chesapeake Bay Program’s Fish Passage Workgroup are helping to remove barriers such as dams and culverts where they block waterways and prevent river herring from migrating. Where structures are unable to be removed, fish ladders and lifts help fish get over or around larger barriers.