Fishery Bulletin 120(2) 
samples (Fig. 2). Multiplying SSFO by the estimates of 
consumption computed by Scordino et al. (2022), we found 
that Steller sea lions ate an average of 714.1 t of coho 
salmon per year and that California sea lions ate 550.4 t of 
coho salmon from spring through fall during 2010-2013 
(Table 4). Chinook salmon composed 0.8% of the diet of 
both California and Steller sea lions (Suppl. Table 3) (online 
only), with average estimates of consumption of 93.6 t per 
year for Steller sea lions and of 74.1 t for California sea 
lions from spring through fall during 2010-2013 (Table 4). 
Proportionally assigning unidentified salmon bones to a 
salmon species on the basis of the frequency it was identi- 
fied, we computed that Steller sea lions ate an average of 
861.7 t of coho salmon and 116.4 t of Chinook salmon per 
year and that California sea lions ate 601.0 t of coho 
salmon and 80.9 t of Chinook salmon from spring through 
fall in each year (Suppl. Table 4) (online only). 
Blind study of identification accuracy 
Fifteen samples were provided to our laboratory team for 
a blind analysis of identification accuracy. The team was 
able to identify the species for 13 of the 15 samples, and 
the identification was accurate for all 13 samples. 
Comparison of salmon consumption by sea lions 
to fishery landings 
We compared consumption of each Pacific salmon species 
by California and Steller sea lions to commercial fisher- 
ies landings of Pacific salmon on the coast of Washington 
and in all of Washington State (Table 5). Steller sea lions 
consumed more coho salmon, chum salmon, pink salmon, 
and steelhead than were landed in commercial fisheries 
at coastal ports in Washington. In addition to the species 
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Figure 2 
Split-sample frequency of occurrence of salmon species identified in samples of 
California sea lion (Zalophus californianus) and Steller sea lion (Eumetopias 
jubatus) scat collected in northwest Washington from 2010 through 2013. The 
Unidentified category is for salmon bones found in scat samples that we were 
unable to identify to species through genetic analysis. 
listed for Steller sea lions, California sea lions also con- 
sumed more sockeye salmon per year than were landed in 
commercial fisheries in coastal Washington. In contrast, 
the combined estimates of consumption for both species of 
sea lions for Chinook salmon of all size classes was roughly 
8.5 times less than the commercial landings of Chinook 
salmon in coastal Washington. To compare consumption 
to statewide commercial fishery landings, we combined 
the consumption estimates for California and Steller sea 
lions for all size classes of Pacific salmon. We found that 
California and Steller sea lions eat more steelhead than 
are landed in commercial fisheries throughout the state 
of Washington. The total estimated consumption of all size 
classes of coho salmon by California and Steller sea lions 
of 1462.8 t is similar to the statewide landings by the com- 
mercial fishery of 1646.8 t. 
Fisheries generally target Pacific salmon that we would 
classify as large salmon in our study of consumption of 
salmon by California and Steller sea lions. Commercial 
fisheries on the Pacific coast of Washington landed more 
Pacific salmon of each species, with the exception of sock- 
eye salmon, than our minimum estimate of consumption 
of large Pacific salmon by sea lions (Table 5). 
Discussion 
This study is the first to rigorously evaluate consump- 
tion of Pacific salmon by California and Steller sea lions 
in Washington State. We found significant differences 
between California and Steller sea lions in the size 
class of Pacific salmon consumed, with Steller sea lions 
more frequently consuming salmon in the small size class 
despite being the larger of the 2 sea lion species (Wynne, 
1993). Coho salmon was the most frequently consumed 
salmon for both California and Steller 
sea lions. This result was not surprising 
for small Pacific salmon because coho 
salmon are the most abundant juvenile 
salmon off the coast of Washington, fol- 
lowed by Chinook salmon (Pearcy and 
Fisher, 1990). In addition to being more 
abundant, juvenile coho salmon are typ- 
ically distributed at shallower depths 
in the water column than the depths at 
which Chinook salmon are found (Beam- 
ish et al., 2018), likely increasing their 
vulnerability to predation by sea lions. 
When consuming large Pacific salmon, 
California and Steller sea lions most fre- 
quently consumed coho salmon despite 
the greater abundance of returning 
adult pink, sockeye, and chum salmon 
migrating through the study area (Losee 
et al., 2019; Walters et al., 2020). 
The total mass of coho salmon con- 
sumed by California and Steller sea 
lions in northwest Washington was simi- 
lar to the mass of coho salmon landed by 
