Blueback Herring

Alosa aestivalis

Quick Facts

  • Species

    Nonnative

  • Habitat

    The preferred habitat of blueback herring depends on its age and surrounding species. Blueback herring spawn in brackish water or freshwater rivers over areas with gravel, sand, detritus or underwater grasses. In areas where alewife and blueback herring co-exist, blueback herring will expand their spawning site range to shallow areas covered with vegetation, ricefields, swampy areas and small tributaries. Juvenile blueback herring leave these areas and swim out to sea, some migrating more than 1,200 miles in the Atlantic Ocean.

  • Range

    The range of blueback herring extends from the lower parts of Cape Breton rivers in Nova Scotia, Canada, and south to the St. Johns River in Florida, and west to the Great Lakes. They can be found throughout the Chesapeake region.

  • Diet

    Plankton, small crustaceans and fish eggs

  • Lifespan

    8 years

  • Status

    Threatened

The blueback herring is a small, silvery fish that migrate from the brackish waters of the Chesapeake Bay to the open ocean. 

Appearance

The blueback herring is a silvery fish with a blueish green back and dark spots on its shoulder. It also has spiny scales, called scutes, along its belly. Its fins are slightly yellow to green, with a branched pelvic fin and a short anal fin. The blueback herring can be difficult to distinguish from the alewife, but blueback herring have smaller eyes and are smaller overall, at 11-15 inches. 

Feeding

River herring feed on plankton, shrimp, fish eggs and small crustaceans like copepods and amphipods. 

Predators

Blueback herring are part of the forage base for large predators, such as striped bass and bluefish, but are also preyed upon by gulls, terns and other coastal birds. They are also threatened by habitat impediments like dams, habitat degradation and loss and commercial and recreational fishing. Dams block rivers that lead to spawning migrations and urban development produces pollution. These threats have restricted the habitat range of blueback herring. 

Reproduction and Life Cycle

As anadromous fish, blueback herring migrate inshore and up rivers to spawn in fresh or slightly brackish water with an outlet to the sea in late spring. Males reach maturity earlier than females and are smaller. Female blueback herring reach maturity between ages three to five, and can lay 30,000 to 400,000 eggs each. The eggs are yellowish and semi-transparent. Males and females release their sperm and eggs simultaneously into the water.  After spawning, adults immediately migrate downstream. Once hatched, juvenile blueback herring remain in freshwater nursery areas in spring and summer, feeding mainly on zooplankton until the water temperatures fall. As it gets colder, the juveniles move downstream to saltier waters and eventually out to sea. 

Did You Know?

  • Blueback herring are an anadromous species, which means they can live in both fresh and saltwater. 
  • Blueback herring have spawning marks on their scales recording the number of times each individual fish has spawned in its lifetime.  
  • Blueback herring come to the surface when the sun is shining, and go deeper into the water on darker days. 
  • Adult blueback herring migrate coastward in response to changes in water temperature and light intensity.

Sources and Additional Information

Quick Facts

  • Species

    Nonnative

  • Habitat

    The preferred habitat of blueback herring depends on its age and surrounding species. Blueback herring spawn in brackish water or freshwater rivers over areas with gravel, sand, detritus or underwater grasses. In areas where alewife and blueback herring co-exist, blueback herring will expand their spawning site range to shallow areas covered with vegetation, ricefields, swampy areas and small tributaries. Juvenile blueback herring leave these areas and swim out to sea, some migrating more than 1,200 miles in the Atlantic Ocean.

  • Range

    The range of blueback herring extends from the lower parts of Cape Breton rivers in Nova Scotia, Canada, and south to the St. Johns River in Florida, and west to the Great Lakes. They can be found throughout the Chesapeake region.

  • Diet

    Plankton, small crustaceans and fish eggs

  • Lifespan

    8 years

  • Status

    Threatened