Chesapeake Bay Field Office
Northeast Region

Alewife (alosa pseudoharengus) and Blueblack Herring (alosa aestivalis)

Life History
When ready to spawn, adults usually return to the same water in which they were born, although some straying does occur. No one knows exactly how they do this. Many scientists believe this homing instinct is due to a special sensitivity to magnetic signals, polarized light and unique characteristics of the natal stream.

The onset of spawning is related to water temperature and length of day. Spawning season for alewife generally runs from March through April. Blueback spawn from mid-April through late May.

Blueback herring prefer to spawn in swift water, while alewife favor slow streams. Upon reaching the spawning ground, males circle a lone female. As this mass of fish swirls around, the females releases her eggs and the males release their sperm. After spawning, the adults swim back downstream and return to the ocean.

The eggs hatch in three to seven days. Swift flowing streams carry the larvae downstream. In Chesapeake Bay rivers, juveniles range throughout tidal and freshwater areas during the spring but move upstream during summer with the encroachment of saltier water. During fall, the water the young move downstream, beginning their first seaward migration. Juvenile river herring remain at sea until reaching sexual maturity in 3 to 6 years.

Herring are food for estuarine and coastal predators, including striped bass. Historically, the ample supply of river herring supported a large fishery. Colonists stored salted herring in for winter food and used the oily backbones of blueback herring as lamp wicks.

The Fishery
Herring are still harvested. They can be eaten fresh, pickled or smoked. Herring are also harvested for their roe (eggs). The majority of commercially harvested herring, however, usually ends up as crab and eel bait, fish meal, or pet food.

Commercial landings of herring in the Bay peaked in 1908 at nearly 66 million pounds. By the early 1970s herring stocks dropped dramatically and commercial harvests plummeted. From 1965-1985, harvests of herring in Maryland and Virginia declined by at least 80%.

A variety of factors has contributed to this decline. Between 1967 and 1977, foreign offshore fishing caught huge quantities of herring as the fish tried to migrate.

Recent depletion of river herring has been attributed to overfishing, pollution, and loss of spawning habitat. Spawning river herring must run a gauntlet of fishermen equipped with nets and rods. Pollution such as sediment runoff or acid rain can kill sensitive larval fish. In addition, dams, road culverts, stream gauging stations, and debris impede herring migration. These blockages have eliminated nearly 1,000 miles of potential spawning habitat in Chesapeake Bay tributaries.

The decline of river herring has had significant economic and ecological impacts. Thriving herring runs offer sport and commercial fishing opportunities. In addition, they are a valuable food for fish, mammals, amphibians, and birds. Largemouth bass, white and yellow perch, and other fish feed on juvenile herring. Adult herring are consumed by a variety of birds.

Restoring Herring
Of all anadromous fish in the Chesapeake, herring have dropped most dramatically. Only a few rivers support healthy populations.To restore herring and other anadromous fish, historic migration paths and spawning grounds must be improved and in some cases re-established.

Where possible, barriers such as dams, culverts, and debris are removed. Construction of artificial passageways, like fish ladders and lifts, help fish get over or around larger dams. Since 1989, almost 200 miles of spawning habitat has been restored and more rivers are slated for opening. Additional restoration efforts include restocking depleted streams with herring transferred from other river systems.

The water quality of spawning and nursery habitat must also improve. Citizens can help. Maintaining streamside forests or vegetative buffers, and reducing the amount of nutrients applied to farms and yards, are two simple ways to protect the water quality of spawning grounds. Ultimately, habitat must be restored and protected to ensure abundant spawning runs of river herring in the Chesapeake Bay watershed.

Find out about these fish in Chesapeake Bay

Striped Bass


American Shad

Atlantic Sturgeon

For centuries throughout the Bay watershed, fishermen lined the banks of rivers and streams dipnetting for alewife and blueback herring as the fish made their annual spawning runs. Once so abundant, the fish were often referred to as glut herring.

Commonly known as river herring, both fish are anadromous, spending living in the ocean but migrating to freshwater to spawn. The blueback herring is silver with a bluish back, while the alewife, also silver, has a bronze-green back. Both share a single dark shoulder spot and vary in length from 12 to 15 inches when fully grown.

Last updated: January 28, 2011