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Diadromous FishAlison BowdenCHAPTER6IntroductionDiadromous fish share one major attribute. They exploitboth freshwater and saltwater habitats during distinctphases of their life cycles. The distance they travel inorder to do this varies widely among species, from therainbow smelt that lives its entire life within about a mileof the coast up to the head of tide in rivers, to the Atlanticsalmon that travels thousands of miles from the oceanwaters off Greenland to headwater streams hundreds ofmiles inland. Because their life histories link terrestrial,freshwater, and marine ecosystems, they are an idealconservation target for ecosystem-scale initiatives. Thestress and depletion of energy stores required to transitionbetween fresh and salt water render these speciesextremely vulnerable to habitat degradation within freshwater and marine migratory corridors, and much of their historicfreshwater spawning habitat is no longer accessible, having been blocked by dams and other barriers. The combinationof habitat impacts, excessive predation and fishing pressure, both from directed fisheries and bycatch, has caused significantdeclines in populations of these species. For example, American shad is estimated to occupy about half of its historicspawning rivers coastwide at 10% of historic abundance (ASMFC 2007). The cultural importance of these species is evident:Several of these species have been featured in popular literature, from Henry David Thoreau’s lament of the loss ofherring runs due to dam construction on the Concord River in 1839 to John McPhee’s account (2002) of the natural andsocial history of American shad in The Founding Fish.Technical Team MembersColin Apse, The Nature Conservancy, Eastern DivisionMichael Armstrong, Ph.D., Massachusetts Division of Marine FisheriesAlison Bowden, The Nature Conservancy, MassachusettsMark Bryer, The Nature Conservancy, MarylandMari-Beth DeLucia, The Nature Conservancy, New YorkMichele DePhilip, The Nature Conservancy, PennsylvaniaAndrew Manus, The Nature Conservancy, DelawareJake Kritzer, Ph.D., Environmental Defense FundMartha Mather, Ph.D., University of Massachusetts/USGS Cooperative Fish and Wildlife UnitJay Odell, The Nature Conservancy, VirginiaArlene Olivero, The Nature Conservancy, Eastern DivisionJoshua Royte, The Nature Conservancy, MaineGeorge Schuler, The Nature Conservancy, New YorkGeoffrey Smith, The Nature Conservancy, MaineAdam Whelchel, Ph.D., The Nature Conservancy, Connecticut© William W. Hartley, U.S. Fish & WildlifeNorthwest Atlantic Marine Ecoregional Assessment • Phase 1 Report 6-