Comprehensive DescriptionRead full entry
BiologyAmphihaline species (Ref. 51442), schooling and strongly migratory (Ref. 188). Adults are usually found in open waters along the coast (Refs. 59043, 89486); juveniles are usually found along estuaries and near the shore (Ref. 59043), possibly making vertical diurnal movements synchronized with the tides; they remain in estuaries for over one year (Ref. 89630). Migrates to major rivers to spawn; also reported to spawn in small rivers. Several landlocked (lake) non-migratory populations exist (Ref. 10541). Ichthyophagous, feeds on small fishes and crustaceans, the young taking the fry of herrings, sprats and gobies (Ref. 188, Ref. 51442). Females grow faster and are always larger than males of the same age (Ref. 10541). Very locally distributed due to pollution and impoundment of large rivers throughout Europe and most populations declined during the first decade of the 20th century, but seem to have stabilized at a low level since then (Ref. 59043). It has been suggested that members of the genus Alosa are hearing specialists with the American shad (Alosa sapidissima) having been found to detect and respond to sounds up to at least 180 kHz (Ref. 89631). This may aid in predator avoidance (e.g. cetaceans) (Ref. 89632). Hybridization between this species and the allis shad (Alosa alosa) has been reported from the Rhine (Ref. 89633) as well as rivers in France and Algeria (Ref. 10541). There is some evidence that indicates that shad hybrids may reproduce (Ref. 27567).