Van Doornik et al.: Stock-specific distribution of juvenile Oncorhynchus mykiss during early marine migration 
99 
126°W 
44°N — 
40°N — 
48°N 
120°W 
114°W 
I 
Genetic stock group 
O Puget Sound/Strait of Juan de Fuca 
O Washington coast 
• Lower Columbia River summer run 
O Lower Columbia River winter run 
O Middle and Upper Columbia River/Lower Snake River 
© Middle and Upper Snake River 
O Oregon coast 
O Klamath Mountains Province 
O Northern California 
• Central Valley, California 
O Ocean sampling locations 
Figure 1 
Map showing the sampling locations for steelhead (Oncorhynchus mykiss ) used in a 
baseline of genotypic data for populations assigned to each genetic stock group. Also 
shown are the locations of ocean sampling, conducted for this study in 2006-2012 
along 7 latitudinal transects called (from north to south) Father and Son, LaPush, 
Queets River, Grays Harbor, Willapa Bay, Columbia River, and Cape Meares. 
Fisheries Science Center collected genotypes for sam¬ 
ples collected from coastal rivers of Oregon and Cali¬ 
fornia (data available from website, accessed December 
2017). The compiled baseline consisted of genotypes of 
9934 steelhead from 148 populations (Table 1, Fig. 1). 
Ocean-caught samples were obtained as part of a 
much larger project studying the early marine ecol¬ 
ogy of salmon from the Columbia River (Brodeur et al., 
2000; Brodeur et al., 2005). The steelhead samples used 
in this study were collected from trawl hauls made in 
May in each year of the period 2006-2012. Sampling 
was conducted off the coasts of Washington and Oregon 
along 7 transects, from 48°13.7'N to 45°29.0'N (Fig. 
1), by towing a Nordic 264-rope trawl (Nor’Eastern 
Trawl Systems, Inc. 2 , Bainbridge Island, WA) at a 
2 Mention of trade names or commercial companies is for iden¬ 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
speed of approximately 1.6 m/s for 30 min (Brodeur et 
al., 2005). The same vessel, gear, trawling depth, and 
speed were implemented each year. At the time of cap¬ 
ture, fish were identified to species, measured (in fork 
length), and then frozen on board the sampling vessel. 
In the laboratory, fish were thawed, re-measured, and 
examined for marks indicating hatchery origin, such 
as adipose fin clips or coded-wire tags, and a portion of 
their caudal fin tissue was preserved in 100% ethanol. 
Procedures for genotyping samples differed slightly 
among the laboratories contributing data to this proj¬ 
ect, but all were similar to the method described by 
Hess et al. 1 . In general, fish were genotyped for 131 or 
180 single nucleotide polymorphism (SNP) loci (Hess 
et al. 1 ) by amplifying loci of interest through the use 
of polymerase chain reactions (PCR). The resulting 
PCR products were then visualized by using genotyp¬ 
ing platforms from either Fluidigm Corp. (South San 
Francisco, CA) or Illumina, Inc. (San Diego, CA). 
