Blueback Herring

The Blueback Herring is a small, silvery anadromous fish in the herring family (Clupeidae), closely related to the Alewife and found along the Atlantic coast of North America from Nova Scotia to Florida. Classified in the genus Alosa, it spends most of its adult life in coastal ocean waters before migrating into freshwater rivers each spring to spawn, typically slightly later in the season and in warmer water than the closely related Alewife. Blueback Herring are an important forage species along the Atlantic coast and have experienced significant population declines in many rivers due to dam construction blocking spawning migrations, prompting fish-passage restoration efforts in several watersheds.

Field marks:

• Slender, laterally compressed body, silvery sides and belly
• Deep blue-green back, more intensely colored than the grayer-backed Alewife
• Single dark spot positioned just behind the gill cover
• Comparatively small eye relative to head size, smaller than in Alewife
• Sharp, saw-toothed scutes along the belly midline
• Deeply forked tail
• Adults typically 25-32 cm

Blueback Herring are best distinguished from the very similar Alewife by their smaller eye, more intensely blue-green back coloring, and a dark or dusky (rather than pale) lining inside the body cavity.

Blueback Herring inhabit coastal Atlantic waters from Nova Scotia to Florida as adults, migrating into coastal rivers and tributaries to spawn each spring. They tolerate a wide salinity range, moving between marine, estuarine, and freshwater habitats over their life cycle. Compared to the Alewife, Blueback Herring tend to spawn slightly later in the season and favor somewhat warmer water and faster-flowing river reaches. Juveniles rear in freshwater and brackish nursery habitat before migrating to the ocean, where adults spend the majority of the year in coastal shelf waters.

Blueback Herring are anadromous, undertaking coordinated spring spawning migrations from coastal ocean waters into freshwater rivers, generally following shortly after Alewife runs in the same watersheds. They form large schools both at sea and during migration, feeding on zooplankton by filtering with fine gill rakers. Spawning occurs in flowing water over sand, gravel, or rocky substrate, with adults broadcasting eggs and sperm in open water; many individuals survive to spawn in subsequent years. As both a prey species and a plankton consumer, Blueback Herring play a significant role in coastal and riverine food webs, supporting populations of predatory fish, seabirds, and other wildlife along the Atlantic seaboard.