Alewife
Alosa pseudoharengus
Profile / Morphology 2
The alewife (Alosa pseudoharengus) is a species of fish. The front of the body is deep and larger than other fish found in the same waters, and its common name is said to come from comparison with a corpulent female tavernkeeper ("ale-wife").
Alewife are a medium-sized, relatively deep bodied and laterally compressed fish. The species coloring is grayish green above, darkest on the dorsal surface, and silvery on the ventral surface and sides. There is often a dusky spot on adult fish that is located at eye level on either side, behind the margin of the gill cover (Collette and Klein-MacPhee 2002). Alewife are distinguished from other Atlantic herring by differences in body depth, origin of the dorsal fin, coloration patterns, and serrations on the ventral surface midline. They also appear similar to young American shad, although there are differences in jaw length and projection, body shape, and numbers of gill rakers (Collette and Klein-MacPhee 2002). Blueback herring are similar in appearance to alewife. However, they can be distinguished by differences in eye diameter, body depth, and the color of the peritoneum – the abdominal cavity membrane (Collette and Klein-MacPhee 2002).
Diet 3
Juveniles feed on zooplankton. Adults feed on small fishes.
Average lifespan in the wild 3
10 years
Size / Weight 3
15 inches maximum / 4 lb maximum
Habitat 3
Alewife 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). According to Collette and Klein-MacPhee (2002), they are also light sensitive and are usually found in deeper water during the day. Diel migrations by adults may also 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. Alewife are euryhaline. They do not spend a large part of their life in estuaries, and migrate between the sea and freshwater habitats.
Range 3
Historically, they were found from Newfoundland, Canada as far south as South Carolina. However, alewife have not been documented this far south in recent years and only occur as far south as North Carolina (ASMFC 2005).
Reproductive / Life Span 3
The alewife is an anadromous species and migrates from adult ocean habitat into freshwaters to spawn in the spring. Spawning migrations begin in the southern portion of the range moving progressively northward and are initiated when water temperatures reach approximately 41 to 50ºF (5-10ºC) (Collette and Klein-MacPhee 2002). Alewife broadcast spawn over a wide range of substrates, such as gravel, sand, detritus, and submerged aquatic vegetation. These substrates are found in large rivers, small streams, ponds, and large lakes. Spawning generally takes place when water temperatures are between 61 and 66ºF (16-19ºC) (Kocik 2000).
Alewife 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 adults reach sexual maturity by age four. Females are capable of producing between 60,000 and 300,000 eggs annually throughout their range (Kocik 2000).
Juveniles remain in freshwater and descend toward the sea in summer and autumn, or even as late as November or December. 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). Bentzen and Paterson (2005) also found that there are significant genetic differences between alewife from the St. Croix River and populations in the LaHave and Gaspereau Rivers (Bentzen and Paterson 2005). They also found some genetic differences between two different tributaries to the St. Croix – Dennis Stream and Milltown. These results indicate that alewife do home to their birth streams. Alewife lifespan is about 10 years.
Relatives 3
Alewife belong to the family that 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. They 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), and ACE Basin (SC).
Water quality factors needed for survival 3
•Water Temperature: spawning occurs between 16 and 19 °C, upstream migrations to spawn occur from 5 to 10 °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
Alewife populations have exhibited drastic declines throughout much of their range. They are often caught with blueback herring, another species of concern. It is difficult to tell these two species apart, so much of the following discussion considers these two species together. The alewife and blueback herring are generally called “river herring”.
There are several threats that have most likely contributed to the alewife’s decline. These threats include:
•Loss of habitat due to decreased access to spawning areas from dam construction and other impediments to migration
•Habitat degradation (silt run-off, loss of wetlands, agricultural practices)
•Overharvesting of fisheries
•Bycatch
•Increased predation from recovering striped bass populations
Conservation notes 3
River herring are taken as bycatch in ocean commercial fisheries using gillnets, bottom otter trawls, and menhaden purse seines (ASMFC 1999).
In the 1930’s, alewife spread into the Great Lakes through the Welland Canal. This landlocked alewife population became very abundant, and has caused many problems by competing with native Great Lakes species. Because they are not native to the Great Lakes, scientists and managers still consider alewife a species of concern because it is at risk in its native range. Also, species living in areas where they are not native often evolve new traits in their biology that make them less like their ancestors in their native areas.
Importance to Humans and Estuaries
Alewife support commercial and recreational fisheries throughout their range. In the past, they were used as bait for crab and lobster fishing. Due to declining trends for river herring, the states of Massachusetts, Rhode Island, Connecticut, and North Carolina have instituted moratoriums on taking and possessing river herring. In many areas, alewife occurred in high numbers. Alewife are migratory, and were once considered a significant source of nutrients being brought into and out of estuaries. Alewife served as prey for many larger predatory fishes.
How to Help Protect This Species
Since these species use estuaries and freshwater habitat, they are susceptible to water pollution, plus damage to and alteration of stream channels and riparian zones. Some suggested methods to help the species include:
•Minimize runoff of neighborhood pollutants, fertilizer, and sediment into local streams, plus other stream and estuary dwelling species.
•Join a stream or watershed advocacy group to protect local estuary ecosystems
•Advocate the implementation of effective fish passage solutions, so fish can bypass dams and artificial barriers.
•Support restoration of more 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 poorly studied areas of the marine phase. Genetic analyses are needed to determine if there are any distinct subpopulations. There is a need to measure population sizes in poorly studied river systems.
Sources and Credits
- (c) Geoffrey Gilmour-Taylor, some rights reserved (CC BY-NC-SA), https://www.flickr.com/photos/giltay/13883951882/
- Adapted by GTMResearchReserve from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Alosa_pseudoharengus
- (c) GTMResearchReserve, some rights reserved (CC BY-SA)
