Blueback Herring
Alosa aestivalis
Fish Illustrations by: Roz Davis Designs, Damariscotta, ME (207) 563-2286
With permission, the use of these pictures must state the following: Drawings provided courtesy of the Maine Department of Marine Resources Recreational Fisheries program and the Maine Outdoor Heritage Fund.
Common name: Blueback herring, blueback shad, river herring
Scientific name: Alosa aestivalis
Range: Blueback herring are anadromous migratory fish, distributed along the Atlantic coast of North America from Nova Scotia, Canada to northern Florida, though are most abundant in waters from the Chesapeake Bay south. Their range and abundance has shrunk considerably over time, and were historically more abundant and widely distributed in river systems along the east coast.
Identification: Blueback herring are overall silvery in color, characterized by the deep bluish-green color on their backs. They have a series of scutes (modified scales that are spiny and keeled) along their belly. On average, blueback herring grow to be 10 to 11 inches in length and 8 to 9 ounces in weight. However, the largest recorded blueback was nearly 16 inches long.
Blueback herring are almost visually identical to alewives, and fishermen in Maine often use the word “alewife” to refer to both alewives and bluebacks. However, there are ways to tell them apart. Bluebacks have a smaller eye (diameter less than or equal to snout length), and a slightly shallower body depth. Spawning location can also indicate species, since bluebacks will spawn in flowing water whereas alewives stick to slack water. However, the best way to tell them apart is to look at their peritoneum (the lining of the abdominal cavity). If you were to cut each open, the body cavity in the blueback herring is dusky black while the alewife's is pinkish-gray.
Life history: The life history of the blueback herring is similar to that of the closely related alewife. Both species are anadromous, which means that they live in the ocean, but migrate into freshwater habitats to spawn. While blueback herring will spawn from northern Florida to Nova Scotia, they prefer slightly warmer water. As a result, they tend to have a more southern distribution than alewives, and are less common in Maine.
Spawning occurs in late spring (May-June) in the northern part of their range. When rivers begin to warm and reach about 57°F, adult blueback herring migrate up coastal rivers to spawn. They will deposit their eggs in large rivers, small tributaries upstream from the tidal zone, and even in brackish waters, with an overall preference for fast moving water over hard substrates. Depending on water temperature, the eggs hatch in 3 to 6 days. The young fish spend their first summer (3-7 months) growing rapidly in freshwater until they are large enough (generally 3-4 inches) to start their journey back to the ocean. The exact length of this period depends largely on the average water temperature.
With the approach of cooler water temperatures in the fall, most juvenile blueback herring begin their migration back out to the ocean. Once they are out at sea, they undertake seasonal migrations along the Atlantic Coast. They stay in the ocean until they reach maturity after 3 to 4 years in males and 4 to 5 years in females, then return to the river where they hatched to spawn a new generation of fish. Blueback herring may live up to 8 years and can spawn multiple times if they survive. Repeat spawners are an important component of populations as larger females produce more eggs and help with population resilience under variable and changing environmental conditions.
Behavior and Diet: Once in the ocean, blueback herring travel along the coast in large schools, feeding on plankton and small fish for most of the year. The Gulf of Maine is a known summer feeding area for many east coast stocks. Blueback herring are vertical migrators: following the diel movements of zooplankton in the water column. However, blueback herring are typically found higher in the water column than alewives.
Ecological importance: As part of the “river herring” group, blueback herring are a vital component of freshwater, estuarine, and marine environments in Maine for the same reasons that alewives are. They are an important forage base, and both freshwater and marine fishes, like striped bass and bluefish, feed on blueback herring. Marine mammals and birds, like seals, ospreys and bald eagles, among others, also feed on blueback herring.
Cultural importance: Before European settlers arrived in Maine, river herring were plentiful in the rivers and ponds, and provided a bountiful source of food for people and wildlife for thousands of years. The Passamaquoddy at Sipayik describe river herring as “the fish that feeds all”. Historical accounts describe spring herring runs as being so large one could “walk on the backs of the fish” to cross rivers.
River herring were also important for early settlers and their communities. The spring runs would bring people together to catch and process large volumes of fish each year, and provide a way for communities to catch up with one another after winter. River herring have also been used for fish meal and fish oil to be added to fertilizer, pet food and domestic animal feed, and today the fish are used primarily as spring lobster bait.
Threats: Blueback herring numbers have declined significantly throughout their range. The main challenges blueback herring face are obstacles to fish passage, climate change, fishing pressure, and pollution. Over the years, river herring populations have declined due to habitat loss associated with dams, road crossings and other development activities, overfishing as a direct fishery and as bycatch, pollution, and other factors.
The hundreds of dams found along Maine’s rivers are remnants of a long and productive history of industry in the state. However, dams and other barriers like hung culverts or beaverdams can block fish migration and prevent them from reaching their spawning grounds.
In addition to unsustainable fishing practices in the last century, river herring are currently caught as bycatch in Atlantic herring and mackerel fisheries. There are efforts to limit this bycatch, however, and commercial fishing is collaboratively regulated through federal, state and local groups. Pollution and effects from climate change are additional concerns, because of the species’ reliance on specific water temperatures, consistent river flows, and good water quality.
Restoration efforts: Dam removals are the best long term strategy for restoring river herring runs. Fish passage construction is the best option for restoring river herring populations to rivers where dams are unlikely to be removed. However, blueback herring may be more reluctant to use certain fishways compared to alewives.
Some stocking of adult river herring has occurred in the northeast, as part of a larger restoration plan. However, success of the plan will largely depend on continued improvements in fish passage, and restoring access to as much natural spawning habitat as possible.
Fishery: Alongside alewives, blueback herring were once part of the largest and oldest commercial and recreational fishery on the Atlantic Coast. However, as a result of population declines, the fishery no longer supports anywhere near the same numbers as in the past. Today, river herring are harvested commercially both for human consumption and for bait, though the latter is the more common usage. Adult river herring are the preferred bait for the spring lobster fishery, when other bait options are limited. No commercial distinction is made between blueback and the more abundant alewife; the species are equally useful for bait, for food, and are harvested and marketed in a similar fashion. Management of the fishery in Maine is a cooperative effort between the Maine Department of Marine Resources and municipalities. Fishing privileges are often leased to independent fishermen, and regulations limit harvest through time and area closures as well as gear restrictions. There is also a small recreational fishery for river herring, and the same restrictions apply as for commercial fishing.
Sources:
https://www.fws.gov/species/blueback-herring-alosa-aestivalis
https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=488
https://www.wildlife.nh.gov/fishing-new-hampshire/fish-species-nh/blueback-herring
https://www.fisheries.noaa.gov/species/river-herring
https://www.gomriverherringnetwork.org/about-river-herring
http://www.downeastfisheriestrail.org/fisheries-then/alewives-and-blueback-herring/