Alewife

The alewife (Alosa pseudoharengus) is a small to medium-sized fish in the herring family (Clupeidae). It is an anadromous species native to the western Atlantic, spending much of its adult life in marine and estuarine waters and ascended rivers to spawn in freshwater during the spring.

Distribution and habitat

Alewife populations occur along the Atlantic coast of North America, with runs in many coastal rivers and streams from Newfoundland to the mid-Atlantic United States. Juveniles and adults frequently inhabit nearshore, brackish, and estuarine environments, while spawning takes place in cooler freshwater systems with gravel or sandy bottoms.

Description

The fish has a slender, laterally compressed body with a dark bluish-green back and silvery flanks. It features a single dorsal fin and a forked tail, with a relatively small head and mouth. Typical adult length ranges from about 15 to 25 centimeters, occasionally reaching around 30 centimeters.

Life cycle and reproduction

Alewives are spawned in freshwater in spring. Females release thousands of eggs that are fertilized externally by males; the eggs drift in the current and hatch into alevins, which then become fry. Juveniles migrate to estuarine and coastal habitats as they grow. Age at maturity is typically two to three years, and individuals may live several more years in suitable conditions.

Ecology and human use

Alewives are an important forage species, providing food for larger fish, seabirds, and marine mammals. They have been utilized as bait fish and, in some regions, for human consumption. Populations have fluctuated, influenced by dam construction, habitat loss, and competition with other species. Notably, in the Great Lakes region, alewife abundance contributed to ecological shifts and thiamine deficiency issues in some predatory fish, prompting management responses to balance ecosystems.