Alewife (Alosa pseudoharengus), Blueback Herring (Alosa aestivalis)
Alternate common names for alewife: Sawbelly,
Alternate common names for blueback herring: Blueback, Glut Herring, Big-eye.
Color: Pale white and silvery with a blue black back. Appears iridescent in the water, with shades of green and violet. Single dark spot on the shoulder, just behind the gill cover.
Size: Up to 15 inches long. Females are larger than males.
Habitat: Salt marsh, open water, freshwater rivers, river mouths.
Seasonal appearance: Spring through late fall.
River herring is the general name for two species of fish commonly found in Rhode Island waters, the alewife and the blueback herring. They are similar to one other, differing only slightly in appearance and behavior. The blueback herring is thinner and has a distinctive blue black back, while alewives are thicker and more greenish black. This distinction is most apparent in freshly caught fish.
River herring are also similar to a group of larger herring called shad. River herring are thick around the head and abdomen, narrowing to the tail, with heavy sharp serrations along the underside, hence the nickname "sawbelly." Its scales are large and slough off easily when handled. It has a distinctive dusky grey spot just behind the margin of the gill cover. These fishes have large eyes, lower jaws that project beyond the upper jaw, and toothless mouths.
Life History and Behavior
River herring are anadromous fish that hatch and move out to the ocean where they spend their adult lives before returning each year to spawn in the freshwater streams where they hatched. River herring can often be found in schools of thousands, congregating near natal streams. River herring suffer high rates of natural mortality, with less than one percent of all eggs surviving the harsh migration to salt water as juvenile fish. Adults are capable of spawning more than once, but the rate of repeat spawning is low. Many die due to predation by birds, mammals and fishermen. River herring feed primarily on plankton, including copepods, amphipods, shrimp, and fish eggs. They are preyed upon by striped bass, bluefish, gulls, terns, and other coastal birds.
Adapted from The Uncommon Guide to Common Life on Narragansett Bay. Save The Bay, 1998.