atlanticsalmon columbiariverwatershed conservation conservationofnaturalresources control dams economicaspects ecosystemmanagement effectofhabitatmodificationon effectofwaterlevelson endangeredspecies fishes governmentpolicy habitat habitatconservation history juvenileliterature lawandlegislation management migration northwest pacific pacificsalmonfisheries predatorsof predatorymarineanimals public-privatesectorcooperation reservoirdrawdown salmon salmonstockmanagement sealions socialaspects unitedstates