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Blueback herring (Alosa aestivalis) are anadromous, meaning they spend the majority of their life in the open ocean of the Atlantic and return to freshwater tributaries along the eastern coast of North America to spawn each year (Fuller et al., 2016; U.S. Fish and Wildlife Service, n.d.). When ocean temperatures reach approximately 14°C, blueback herring begin migrating from the open ocean into freshwater systems to spawn. The entire spawning season occurs from late April to mid-September, but the greatest activity is exhibited from mid-May to mid-July. The herring select spawning sites based on the amount of water flow and type of benthic substrate, preferring quick-moving water and hard, stable bottoms (Loesch & Lund, 1977).
The blueback herring fry remain in freshwater streams until they transition into the later juvenile life stage, where they then migrate downstream into estuarine systems (Pardue, n.d.). As estuary water temperatures begin to decline from mid July through early November, juvenile blueback herring begin the migration out of the estuaries into the Atlantic Ocean (“Maine River Herring Fact Sheet,” 2016). The first groups of fish begin this migration when water temperatures hit 21°C and the greatest movement is observed between 14°C and 15°C, then concludes at 10°C (O’Leary & Kynard, 1986).
Pre-adult, juvenile and young-of-year (fish within the first year of hatching), blueback herring are obligate planktivores meaning that they feed on prey such as copepods and cladocerans (water fleas) (Burbidge, 1974; Janssen, 1982). This fish is opportunistic such that if a prey species comes within or above its field of vision, the herring will approach the surface to engulf the prey (Janssen, 1982). As a result of this predation method, young-of-year only feed during daylight (Burbidge, 1974). Adult blueback herring consume a variety of prey including plants, zooplankton, insects, small fish and fish eggs (Simonin et al., 2007).