104 
Fishery Bulletin 11 7(1 -2) 
between the Lower Columbia River winter-run and the 
Middle and Upper Snake River groups. The Lower Co¬ 
lumbia River winter-run group also was found farther 
north (44 km) than the Lower Columbia River summer- 
run group. The average longitude values indicate that 
we tended to catch steelhead at our westernmost (far¬ 
thest from shore) sampling stations. 
Discussion 
Using GSI, we examined the distribution of steelhead 
juveniles off the coast of Oregon and Washington dur¬ 
ing their early marine migration and found differences 
in relative abundance and distribution among genetic 
stocks and years. From this work, we provide the first 
published evidence of stock-specific distributions of ju¬ 
venile steelhead from the Columbia River. Steelhead 
from the Lower Columbia River winter- and summer- 
run groups were found, on average, farther north than 
fish from other genetic stock groups of the Columbia 
River. The simplest explanation for this observation is 
a difference in the timing of marine entry among these 
groups. Lower Columbia River steelhead have been 
observed to migrate through the estuary earlier than 
other genetic stock groups of steelhead from the Co¬ 
lumbia River (Weitkamp et al., 2015). Therefore, at the 
time of our sampling, they had been in the ocean for a 
longer period, giving them more time to travel north. 
We also observed that between the Lower Columbia 
River steelhead genetic stock groups, the winter-run 
fish were found farther north than the summer-run 
fish. Additional analysis of data from Weitkamp et 
al. (2015) revealed that, on average, Lower Columbia 
River winter-run steelhead passed through the estuary 
3.1 d earlier than summer-run steelhead, a finding that 
could explain why we found them farther north, but 
this difference in timing was not significant (£=1.52, 
P=0.203). 
Although our research focused on stocks of steelhead 
from the Columbia River, there were a few interesting 
results regarding other stocks. Of note is the presence 
of fish from the Oregon coast in our catches, indicating 
that not all steelhead from that area migrate directly to 
offshore waters before heading north, as has been gen¬ 
erally accepted (Myers, 2018). Some of these fish may 
have migrated up to 300 km north before they entered 
our study area. However, given the low CPUE values 
for this stock, the majority of them may already have 
been offshore outside of our study area and the few that 
were caught likely were migrating closer to the coast. 
Also, in our study area, we caught steelhead that were 
assigned to the genetic stock group from Puget Sound 
and the Strait of Juan de Fuca, indicating that they 
did not migrate north immediately (we caught them at 
locations that were south of the entrance to the Strait 
of Juan de Fuca, through which they pass). However, 
the Chambers Creek hatchery steelhead stock, a stock 
that originated in Puget Sound, has been raised and 
released extensively by hatcheries in Washington, in- 
48°N 
47°N 
46°N 
4 ^ -fjW 
I 
I 
t + + 
Washington 
CPUE 
• 0.01-0.05 
• 0.05-0.1 
• 0.1-0.15 
Pacific Ocean 
ft 
Columbia River 
Oregon 
Kilometers 
25 
50 75 100 
i 
+ +i + + +H-; 
V 
Genetic stock group 
• Lower Columbia River summer run 
O Lower Columbia River winter run 
45 N 
Mid & Upper Columbia River/Lower Snake River 
Mid & Upper Snake River 
Oregon coast 
Puget Sound/Strait of Juan de Fuca 
( Washington coast 
125°W 124°W 123°W 
Figure 4 
Average latitude and longitude over all years, with 
standard deviations, of the locations where juvenile 
steelhead (Oncorliynchus mykiss) from each genetic 
stock group were caught in 2006-2012 off the coasts of 
Washington and Oregon. The diameters of the circles 
indicate the average catch per unit of effort (CPUE) for 
each genetic stock group. Plus signs indicate locations 
of ocean sampling, and the black dotted line traces the 
180-m depth contour. 
eluding those located on rivers of the Washington coast 
and the Lower Columbia River (Busby et al., 1996). 
Therefore, it is possible that the fish we caught were 
progeny of stock from Chambers Creek released into 
rivers not within the Puget Sound Basin. 
