The project was initiated after detection data from passive-integrated-transponder tags (PIT tags) had shown distinct differences in migration patterns between wild and hatchery fish for three consecutive years. National Marine Fisheries Service (NMFS) investigators first observed these differences in 1989. The data originated from tagging and interrogation operations begun in 1988 to evaluate smolt transportation for the U.S. Army Corps of Engineers. In 1991, the Bonneville Power Administration began a cooperative effort with NMFS to expand tagging and interrogation of wild fish. Project goals were to characterize the outmigration timing of these fish, to determine whether consistent migration patterns would emerge, and to investigate the influence of environmental factors on the timing and distribution of these migrations.