A departure from popular sportfish like salmon and bass, the alewife is something between a small-sized “forage fish” and a trout although they are more closely related to shads. The alewife has a laterally compressed, silver body and a conspicuous eyespot behind its operculum, or the bony flap that protects the gills. Overall, the body is silver in color with a pale belly and a darker, olive-colored dorsal surface. It is important to understand their coloration to tell them apart from a very similar species, the blueback herring (Alosa aestivalis) whose dorsal surface is a silvery blue compared to the alewife’s olive shade.
Alewives are important forage fish for piscivorous fish and birds. They also support a substantial commercial fishery where they are smoked and packed for human consumption or processed into oil and fishmeal for animal feed. When consumed by humans, they are often packaged like sardines and either smoked or pickled.
As small forage fish, they live relatively short lives and can survive up to 10 years although most individuals are eaten long before then. Older fish can grow up to 15 inches in length (38.1 cm). Alewives that survive to adulthood make up a staggeringly small percentage of fish that are born each year and usually average 12 inches (30.5 cm).
Where Are Alewives Found?
Alewives are indigenous to the Atlantic coastlines of North America, primarily along the eastern seaboard of the United States from South Carolina to Nova Scotia, Canada. Populations on the east coast are threatened and therefore the recreational and commercial harvest of these populations is prohibited in states where they occur, like Massachusetts.
Their look-alikes, the blueback herring, occupy a similar range although they can be found as far as Florida. Seafaring adults travel into freshwater rivers and spawn during the late spring and early summer. Their eggs are deposited onto the riverbed and adults who survive this journey return to the ocean. In a few days, juvenile alewives hatch and spend their first summer in freshwater before migrating to estuaries in the late summer and early fall, finally joining the adults in the Atlantic Ocean near the end of their first year.
Landlocked alewives have a somewhat different life cycle. These populations cannot migrate to the ocean and therefore spend most of their lives in deep lakes, using the shallows or connected rivers as spawning grounds. Landlocked alewives spend the cold winter months in the depths of lakes to avoid freezing surface temperatures. It is important to note that most landlocked alewife populations are introduced and can disrupt native ecosystems. These alewives are also 1.5 inches (3.8 cm) shorter on average than their anadromous counterparts.
Are Alewives Invasive?
In some regions, they are invasive, particularly in the Great Lakes Region and the Central Midwest of the United States. In freshwater lakes where alewives are introduced, they compete with native planktivores like young salmon, trout, lake herring, and chubs. In most cases, they outcompete native planktivores and replace natives as the dominant fish in an ecosystem. This can change an aquatic system’s ecology by replacing fish populations that grow into predators with a fish species that remains planktivorous throughout its life.
The alewife has been present in Lake Ontario since the mid to late 1800s, but its status as a fish native to the area has been challenged. Their spread into the other Great Lakes is, however, adventive and they have been stocked in lakes and reservoirs in the eastern and midwestern regions of the United States as a forage fish for larger piscivorous sportfish.
Predatory Pacific salmon were introduced in the 1960s to control alewife populations although the introduction of yet another non-native species to the Great Lakes, which competes with native predators, also impacts this ecosystem, and does not necessarily help restore it.
Is the Alewife a Prey Species?
The alewife is considered a pelagic “forage fish,” meaning that they are heavily predated upon by other animals. Namely, larger fish, like salmon and bass, birds such as the osprey (Pandion haliaetus), and aquatic mammals like the sea otter (Enhydra lutris). Double-crested cormorants (Phalacrocorax auritus) also feed heavily upon alewives. Alewives form large schools to confuse predators and increase their odds of survival. Additionally, to combat heavy predation mortality, female alewives produce hundreds of thousands of eggs, only a percentage of which survive to adulthood. Their role as a forage species is extremely important to their native ecosystems because predatory animals rely on them as a source of food.
While it is a prey species, the alewife is also a predator–of plankton! Alewives are carnivores but, due to their small size, they can only consume small prey items. They feed on zooplankton and very small aquatic invertebrates. Large adults may opportunistically consume small fish or fish eggs.
