Blueback Herring
Alosa aestivalis
Profile / Morphology 2
Blueback herring are a medium-sized, relatively deep-bodied fish. It is grayish green on its back and is silvery on its belly and sides. Blueback herring are distinguished from other Atlantic herring by differences in body depth, origin of the dorsal fin, coloration patterns, and markings on the underside. They also appear similar to young American shad, although there are differences in jaw shape, body shape, and numbers of gill rakers. Blueback herring are similar in appearance to alewife. However, they can be distinguished by differences in eye size, body depth, and the color of the peritoneum which is the abdominal cavity membrane.
Diet 3
Juvenile blueback herring feed predominantly on zooplankton, preying primarily on ctenophores, calanoid copepods, amphipods, mysids, and other pelagic shrimp. While at sea, they also prey on small fishes, such as Atlantic herring, eel, sand lance, cunner and other alewife, as well as eating the eggs/larvae of other fish species (Collette and Klein-MacPhee 2002).
Average lifespan in the wild 3
10 years
Size / Weight 3
They reach 16 inches (40 cm) in length and weigh no more 4 pounds (1.8 kg).
Habitat 3
Blueback herring adults are a pelagic, schooling species. In the ocean, they undertake seasonal migrations, most likely in response to changing water temperatures (Collette and Klein-MacPhee 2002). They are believed to migrate offshore to over winter near the bottom. According to Collette and Klein-MacPhee (2002), they are usually found in deeper water during the day. Diel migrations by adults may be associated with the distribution of zooplankton in the water column (Collette and Klein-MacPhee 2002). Little else is known of the species’ behavior and habitat use in marine environments. Blueback herring are euryhaline. They do not spend a large part of their life in estuaries and migrate between the sea and freshwater.
Range 3
Historically and currently, they are found from Cape Breton, Nova Scotia to the St. John’s River in Florida. This is a more southerly range than their sister species, the alewife.
Reproductive / Life Span 3
The blueback herring is an anadromous species that migrates from adult ocean habitat into freshwaters to spawn in the late spring. They arrive in coastal waters approximately a month later than their sister species, the alewife. Spawning migrations begin in the southern portion of the range and move progressively northward from late March (southern portion of their range) through mid-May (northern part of range) (Collette and Klein-MacPhee 2002).
Blueback herring broadcast spawn over a wide range of substrates such as gravel, sand, detritus, and submerged aquatic vegetation, which are found in large rivers, small streams, ponds, and large lakes. They use a greater variety of habitats in areas where they co-occur with alewife, and spawning sites include areas with submerged aquatic vegetation, rice fields, swampy areas, and small tributaries upstream from the tidal zone (Virginia Institute of Marine Sciences 2003).
Blueback herring lay down spawning marks on their scales so that the number of times an individual fish has spawned in its lifetime is recorded on its scale. Most females reach sexual maturity by age five, and females are capable of producing between 60,000 and 103,000 eggs. Males generally mature between 3 and 4 years of age. Juveniles remain in freshwater for only 1 to 4 months of their lives, until they reach about 2 inches (5 cm) in length, before migrating out to sea. A tagging study conducted on the Saint John River in New Brunswick, Canada indicated that river herring return with accuracy not only to their home rivers but also to birth areas within those rivers (Jessop 1994). Blueback herring lifespan is about 8 years.
Relatives 3
Blueback herring belong to the family that also includes herring, shad, sardines and menhaden. They are closely related to and similar in appearance and biology to their sister species, the American shad and skipjack herring, which occur in the same areas. These species are often caught and confused with blueback herring.
Found in the following Estuarine Reserves 3
They occur in the following NERRs: Wells (ME), Great Bay (NH), Waiquoit Bay (MA), Narragansett Bay (RI), Hudson River (NY), Jacques Cousteau (NJ), Delaware, Chesapeake Bay (MD and VA), North Carolina, N. Inlet-Winyah (SC), ACE Basin (SC), Sapelo Island (GA), and Guano Tolomato Matanzas (FL).
Water quality factors needed for survival 3
•Water Temperature: spawning occurs between 18 and 22 °C, upstream migrations to spawn occur from 8 to 13 °C
•Turbidity: low
•Water Flow: low to moderate
•Salinity: euryhaline - spawn in freshwater streams, adults live in ocean
•Dissolved Oxygen: moderate to high
Threats 3
Blueback herring populations have exhibited drastic declines throughout much of their range. Blueback herring are often caught with alewife, another species of concern, and it is difficult to tell these two species apart. Much of the following discussion considers these two species together. Both species are called “river herring”.
There are several threats that have most likely contributed to blueback herring declines. These threats include:
•Loss of habitat due to decreased access to spawning areas from dam construction and other migration impediments
•Habitat degradation (silt run-off, loss of wetlands)
•Overharvesting of fisheries
•Bycatch
•Increased predation due to recovering striped bass populations
River herring are taken as bycatch in other ocean fisheries in various gear types including gillnets, bottom otter trawls, and menhaden purse seines (ASMFC 1999).
Conservation notes 3
Importance to Humans and Estuaries
Blueback herring support commercial and recreational fisheries throughout their range. In response to the declining trends in river herring abundance, the states of Massachusetts, Rhode Island, Connecticut, and North Carolina have instituted moratoriums on taking and possessing river herring. In many areas, blueback herring had historically occurred in high numbers. Due to their migratory lifestyle, they were a significant source of nutrients being brought into and out of estuaries. This species served as prey for many larger predatory fishes.
How to Help Protect this Species
Bllueback herring use estuaries and freshwater areas as habitat. This makes them susceptible to water pollution and to the effects of damage to and alteration of stream channels and riparian zones. Suggested methods to help this species include:
•Minimize runoff of neighborhood pollutants, fertilizer, and sediment into local streams.
•Join a stream or watershed advocacy group in your area to protect your local estuary ecosystems.
•Advocate the implementation of effective fish passage solutions so fish can bypass dams and artificial barriers.
•Support restoration natural water flow regimes.
•Support conservation programs like the Species of Concern program and other non-governmental organization programs.
•Support research into the ecology of the species, including studies of the marine phase of the populations. Genetic analyses are needed to determine if there are any distinct subpopulations, and there is a need to measure population sizes in poorly studied river systems.
Sources and Credits
- (c) Henry Zbyszynski, some rights reserved (CC BY-NC), https://www.flickr.com/photos/hankzby/1061882246/
- Adapted by GTMResearchReserve from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Pomacentrus_simsiang
- (c) GTMResearchReserve, some rights reserved (CC BY-SA)
