Contemporary Snake River fall Chinook salmon exhibit migration tactics that differ from their historical counterparts, and this may have resulted from several anthropogenic disturbances.
Other species, such as some populations of Chinook salmon, migrate to sea after just a few months of rearing in freshwater, and chum salmon (O. keta) and pink salmon (O. gorbuscha) begin their migration to sea directly after emergence from the gravel.
Finally, the White River drains into Lake Wenatchee, which must be navigated by returning adults and out-migrating smolts; migration through natural lakes is unusual for Chinook salmon, especially in the Columbia Basin.
In most Chinook salmon populations, juveniles begin migration to sea either shortly after emergence in the spring (subyearling migration tactic) or undergo a full year of growth in freshwater before migrating to sea as a yearling (yearling migration tactic).
For our focal Chinook populations, survival during downstream migration is negatively correlated with temperatures over 13°C and positively correlated with flow (Achord et al. 2007).
In the Fraser River, Cultus Lake sockeye (from the lower Fraser) had slower travel speeds during the downstream migration than populations of Chinook, coho, or steelhead from the mid-Fraser River (Figure 4).
Multiple lines of evidence support the conclusion that historically Snake River fall Chinook salmon had a subyearling juvenile migration tactic.
Furthermore, these findings suggest that the circadian clock genes may influence the migration timing of Feather River Chinook, which is consistent with previous studies of Pacific and Atlantic (Salmo salar) salmon (O'Malley et al.
Scale readings from naturally produced Snake River fall Chinook salmon sampled during their upstream migration at Lower Granite Dam from brood years 1994 through 2002 (incomplete returns for BY 2002; Connor et al. 2005 and subsequent unpublished data) indicated that an average of 54% (range 24 82%) of the total returning adult females to Lower Granite Dam had migrated to sea as yearlings.
The migration tactics of Snake River fall Chinook salmon have changed over time.
