Recovering from co-extirpation: The challenge of restoring an ecologically relevant host-affiliate relationship
American eels (Anguilla rostrata) have declined dramatically throughout their range, partially due to the stream barriers blocking migration pathways. Evidence suggests that the the common eastern elliptio mussel (Elliptio complanata) is less abundant and has lower recruitment in rivers and streams above large fish passage barriers. Freshwater mussels are obligate ectoparasites on one or more host fish species to complete their metamorphosis from larvae to juveniles.
Results of host fish studies indicate that American eels are good hosts for E. complanata, which may partially explain data suggesting limited recruitment of E. complanata. Because eels were historically of economic importance and both eels and freshwater mussels contribute essential functions to stream ecosystems, efforts have been made to restore eel populations, particularly around native mussel beds. Effects of experimental stocking on eel and mussel population dynamics are being assessed, but preliminarily show increased recruitment in E. complanata. Alternative methods for restoring eel populations, and thereby E. complanata recruitment, are being tested.