River herring is a collective term for the alewife, Alosa pseudoharengus, and blueback herring, Alosa aestivalis, two anadromous fish species that are related to the American shad. Anadromous fish migrate from the ocean to rivers to spawn. The coastal range of the alewife extends from northeastern Newfoundland to South Carolina, while that of the blueback herring extends from Nova Scotia to Florida. Both species undertake upriver spawning migrations during spring. The American shad, Alosa sapidissima, is the largest of the herring family, and is a favorite Connecticut River sportfish. It also undertakes upriver spawning migration during spring. The historic range of American shad was from the St. Lawrence River to Florida. Shad are still distributed throughout their historic range but shad are most abundant in east coast rivers between Connecticut and North Carolina.
River herring and shad are important to our freshwater, marine and estuarine ecosystems because adult herring and their young provide food for a variety of predators including freshwater gamefish, marine gamefish, osprey, bald eagle, harbor seals, porpoise, egrets, kingfishers, and river otter. Historically, river herring runs into Connecticut rivers and streams numbered into the millions; however, runs have been declining steadily in recent decades. To help restore river herring populations and other anadromous fish, CTDEEP has built fishways at dams, removed dams, and widened culverts to allow fish to bypass barriers to find habitat upstream to spawn.
This group of streams has one fishway where fish are counted. The amount of available habitat upstream of the fishway is expected to increase due to future fish passage projects (e.g. there are upstream dams that will have fishways in the future). Because of this, the number of fish returning in the future will likely increase regardless of survival at sea. These numbers can be used as an index of how restoration is progressing for each watershed over time.