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.
This group of streams has one fishway where fish are counted. The amount of available habitat upstream of the fishway is not expected to increase due to future fish passage projects (e.g. no more upstream dams or all upstream dams are currently passable). Because of this, the number of fish returning year-after-year will likely be due to changes in survival at sea than major changes in freshwater. These numbers can be used as an index for how the species are doing at sea or in general.
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.
Mianus Pond Fishway – This fishway was built by the Town of Greenwich in the mid-1990s and is located at the head of tide on the Mianus River. It provides access to the large Mianus Pond and a short distance of free-flowing stream prior to reaching the next dam. When it first opened, only hundreds of alewives moved upstream. After years of being able to spawn in the pond, the alewives now number over 80,000 annually. This is one of the strongest alewife runs in Connecticut and other species like gizzard shad, trout, and blueback herring also use the fishway. The data on blueback herring is relatively recent but it is believed to be increasing. The Town operates an electronic fish counter and an underwater camera to obtain these data. There are also two eel passes at this dam to help eels get upstream. The Town provides tours upon request.
Brides Brook – This stream flows out of Brides Lake and enters Long Island Sound about a mile downstream at Rocky Neck State Park. The lake is a natural coastal pond where the alewives spawn. The CTDEEP operates an electronic fish counter and a trap at the head of the brook where it flows out of the lake. The trap is on property that is part of a state prison and is closed to the public. This run has been the subject of research in the 1960s and again in the 2000s, some of which is ongoing. The run is one of the best in the state and the trap is used to capture fish for transplanting into other streams to accelerate the pace of restoration. A project during 2010 at Rocky Neck State Park replaced rusting, inadequate pipes with a new open channel. The 2010 run of alewives was the largest on record and it remains to be determined if it was the pipe replacement or just a good year that resulted in the increase.
Latimers Brook – This fishway is one of the oldest in Connecticut and was originally built to trap returning sea-run trout. Small numbers of alewives were transferred from Brides Brook in the 1980s and 1990s and the fishway was modified and a small but stable run of alewife was created. A trap was installed to help biologists capture returning trout and this trap is also used to count returning alewives, which are then released upstream of the fishway.
Connecticut River – The counts of returning diadromous fish are obtained at the first dam on the river at Holyoke, MA. The dam is 33 feet high (hydroelectric project) and there are two multi-million dollar fishlifts operated by the City of Holyoke. The fish are counted visually by staff of the Massachusetts Division of Wildlife using a window in the side of the fishlift exit flume. There are four additional dams with fishways located on the Connecticut River upstream of the Holyoke Dam as well as others on upstream tributaries. More fishways and dam removals are planned as well as improvements to existing fishways. Therefore, the number of fish returning each year is a function of successful reproduction and survival in the river years earlier as well as survival rates in the ocean.