98 
Fishery Bulletin 11 7(1-2) 
Table 1 
Genetic stock groups and run types of the 148 populations of steelhead ( Oncorhynclius mykiss ) used in 
genetic stock identification analyses in this study of the early marine migration of steelhead from the 
Columbia River. The 2 phylogenetic groups or subspecies of steelhead are coastal steelhead (O. mykiss 
irideus ) and Columbia River redband steelhead (O. mykiss gairdnerii ), commonly referred to as inland 
steelhead. 
Genetic stock group 
Phylogenetic 
group 
No. of 
populations 
Run type 
Puget Sound/Strait of Juan de Fuca 
Coastal 
12 
Winter 
Washington coast 
Coastal 
7 
Winter 
Lower Columbia River summer run 
Coastal 
4 
Summer 
Lower Columbia River winter run 
Coastal 
17 
Winter 
Middle and LTpper Columbia River/Lower Snake River 
Inland 
67 
Summer 
Middle and Upper Snake River 
Inland 
28 
Summer 
Oregon coast 
Coastal 
7 
Summer, winter 
Klamath Mountains Province 
Coastal 
3 
Summer, winter 
Northern California 
Coastal 
2 
Summer, winter 
Central Valley, California 
Coastal 
1 
Winter 
of which is commonly referred to as inland steelhead 
(Busby et ah, 1996; Blankenship et al., 2011). Within 
these groups, there are 2 life history types that are 
identified by the time of year when they return to 
freshwater and by their maturity status when they ar¬ 
rive in freshwater. The inland group is composed al¬ 
most exclusively of summer-run steelhead (Busby et al., 
1996). These are stream-maturing steelhead that enter 
freshwater between May and October, when they are 
still sexually immature, and remain in freshwater for 
several months until they mature and spawn. Summer- 
run stocks are present also in populations of coastal 
steelhead, but this group is primarily composed of 
winter-run steelhead. Winter-run steelhead are ocean¬ 
maturing fish that enter freshwater between November 
and April almost fully mature, and they spawn shortly 
after entry into a river. 
Steelhead of the Columbia River out-migrate from 
freshwater to saltwater through the Columbia River es¬ 
tuary in springtime, with peak out-migration occurring 
in mid-May (Weitkamp et ah, 2012; Weitkamp et al., 
2015). They travel through the estuary quickly (Dawley 
et al., 1986) and, after reaching the marine environ¬ 
ment, move quickly into offshore waters before head¬ 
ing north to the Gulf of Alaska (Burgner et al., 1992; 
Brodeur et al., 2004; Quinn and Myers, 2004; Daly et 
al., 2014). This movement contrasts with that of other 
salmonids, such as Chinook (Oncorhyjichus tshawyts- 
cha ) and coho ( O. kisutch) salmon, which remain closer 
to the coast as they migrate northward (Van Doornik et 
al., 2007; Teel et al., 2015). The rapid offshore migra¬ 
tion of steelhead could be related to a need to quickly 
travel to areas where the fish larvae on which they 
prey are more abundant (Daly et al., 2014). However, 
it is not known if there are stock-specific differences in 
routes of early marine migration. 
Variation among individuals in migration routes can 
affect survival (Furey et al., 2015), and, if differences 
in migration routes among stocks exist, factors, such as 
oceanographic conditions, hatchery practices, or man¬ 
agement of water flow through the hydroelectric dams 
of the Columbia River, could affect the survival of dif¬ 
ferent stocks in different ways. Therefore, our goals for 
this study were to determine if there are differences in 
the early marine migration of steelhead among genetic 
stock groups and if any such differences vary from year 
to year. 
Materials and methods 
Sample collection and genotyping 
To estimate the genetic stock to which each juvenile 
steelhead belonged, we first had to create a baseline of 
genotypic data for steelhead populations whose mem¬ 
bers were likely to be found in our study area. No such 
baseline existed; therefore, we compiled genotypic data 
collected by several genetics laboratories based on the 
West Coast of the United States. Data for populations 
of Puget Sound, the Strait of Juan de Fuca, and the 
Washington coast were provided by the Washington 
Department of Fish and Wildlife (T. Seamons, unpubl. 
data). Data for steelhead of the Columbia River were 
obtained from the Columbia River Inter-Tribal Fish 
Commission and Idaho Department of Fish and Game 
(data available from website, accessed January 2016; 
Hess et al. 1 ; Matala et al., 2014). The NOAA Northwest 
1 Hess, J. E., N. R. Campbell, A. R Matala, and S. R. Narum. 
2013. 2012 annual report: genetic assessment of Columbia 
River stocks, 147 p. Div. Fish Wildl., Bonneville Power Ad¬ 
min., U.S. Dep. Energy, Portland, OR [Available from web¬ 
site, accessed July 2018.] 
