Adult coho salmon (Oncorhynchus kisutch) typically enter small coastal streams or tributaries of larger rivers in fall and usually ascend to the headwaters to spawn enabling their progeny to fill habitats throughout the system. Conventional understanding of coho salmon life history presumes that, following emergence from the redd in spring, coho fry take up residency in the stream for a year or more before migrating to sea in spring as smolts (Sandercock 1991). However, large numbers of fry (age 0, 1st year of life), typically move downstream following emergence. Chapman (1962) first coined the term “nomads” referring to those coho fry moving downstream between emergence and October. The movement of nomads downstream following emergence was interpreted as normal behavior, and this movement is still observed in streams from Oregon to Alaska (Salo and Bayliff 1958, Chapman 1962, Crone and Bond 1976, Hartman et al. 1982, Harke and Lucey 1999). The movement in spring often accompanied freshets, although fry were observed moving downstream even during periods of stable flow. This downstream movement was considered a result of either a physical displacement because of streamflow and fry size (Hartman et al. 1982, Tschaplinski 1987), a behavioral response to aggression and territorial space (Chapman 1962, Mason and Chapman 1965), or a result of habitat limitations (Ruggles 1966, Fraser et al. 1983). In an intensive study of the comparative ecology of stream and estuarine-rearing coho, Tschaplinski (1987) found no evidence of density-dependent causes for this migration and concluded from his observations that the fry were physically displaced by rapid currents associated with freshets.