Scordino et al.: Consumption of Oncorhynchus spp. by Zalophus californianus and Eumetopias jubatus in Washington 155 
Of the scat from California sea lions, 37 samples had 
remains of Pacific salmon in the large size class, 10 sam- 
ples had bones of salmon in the small size class, and 
46 samples had bones from salmon of an unclassified size. 
Of the scat from Steller sea lions, 53 samples had remains 
of Pacific salmon in the large size class, 59 samples had 
bones of salmon in the small size class, and 156 samples 
had bones from salmon of an unclassified size. We found a 
significant difference in the proportion of Pacific salmon of 
each size class consumed between California and Steller 
sea lions by pooling samples from spring, summer, and 
fall (Pearson’s 77=6.64, df=2, P=0.036). California sea lions 
more frequently ate large salmon and less frequently ate 
small salmon in comparison with Steller sea lions. 
Through our genetic analysis, the species was deter- 
mined for 305 of the 361 salmon bones analyzed (84.5%) 
(Table 3). For both California and Steller sea lions, coho 
salmon was the most frequently identified salmon spe- 
cies in all 3 size classes (Table 3). Pooling bones of Pacific 
salmon in all size classes from scat samples collected in the 
spring, summer, and fall, we found significant differences 
in the composition of Pacific salmon species consumed by 
California and Steller sea lions (Pearson’s y7=13.22, df=5, 
P=0.021). 
Both California and Steller sea lions had significant dif- 
ferences in the composition of Pacific salmon species they 
consumed by season, with all size classes of Pacific salmon 
pooled (Suppl. Table 1 [online only]; Steller sea lion: y7=98.2, 
df=2, P<0.0001; California sea lion: y7=22.7, df=10, P=0.012). 
Coho salmon was the most frequently identified salmon spe- 
cies in samples of California sea lion scat collected in fall 
and winter; chum and pink salmon were the most com- 
monly identified species from samples collected in spring. 
Coho salmon was the most frequently identified salmon spe- 
cies in samples of Steller sea lion scat collected in the fall, 
spring, and winter; the majority of salmon bones identified 
from samples collected in summer were pink salmon. We 
found no significant differences by size class in the species 
composition of Pacific salmon consumed by California and 
Steller sea lions (Suppl. Table 2) (online only). 
We tested the responses of California and Steller sea 
lions to the large increase of pink salmon available in 2011 
(Losee et al., 2019) by comparing the species composition 
of Pacific salmon consumed between 2011 and 2012. We 
found no significant difference in the annual species com- 
position of Pacific salmon consumed by Steller sea lions in 
2011 and 2012. We further compared Pacific salmon con- 
sumption between years by using only samples collected 
in summer because commercial fishery landings of adult 
pink salmon are typically highest in the study area in the 
summer. We found inconclusive but suggestive evidence 
of differences in the composition of Pacific salmon species 
consumed between summer 2011 and summer 2012 (Fish- 
er’s exact test: P=0.058), with pink salmon accounting 
for a larger percentage of the salmon consumed in 2011 
than in 2012. We had to limit our analysis of the response 
of California sea lions to samples collected in the fall in 
2010, 2011, and 2012 because samples were not collected 
in spring and summer in all years (Table 1). We found sig- 
nificant differences in the composition of Pacific salmon 
species identified by year (Fisher’s exact test: P<0.001), 
with coho salmon being the dominant species among spe- 
cies identified in 2010 and 2012 and chum salmon being 
the dominant identified species in 2011. 
Salmon consumption estimates 
Data on salmon species identified from the genetic analy- 
sis in this study was combined with data on the diets of 
California and Steller sea lions from Scordino et al.” to 
compute the SSFO by Pacific salmon species identified 
and for unidentified salmon by size class. We assumed 
that our calculated SSFO was equivalent to percentage of 
diet (Olesiuk et al., 1990). Coho salmon composed the larg- 
est portion of the diets of California and Steller sea lions 
among the Pacific salmon species identified in scat 
Table 3 
Species composition of salmonids (Oncorhynchus spp.) identified in scat samples of California sea lions (Zalophus cal- 
ifornianus) and Steller sea lions (Humetopias jubatus) collected in northwest Washington from 2010 through 2013 by 
size class and associated sample size of identified salmon and unidentified (Unid.) bones. The size classes of prey species 
are large (>50 cm in total length [TL]), small (<25 cm TL), and unclassified (could not be definitely sorted to the large or 
small size class). 
Prey species identified 
Predator 
Sample size 
species 
California 
sea lion 
Steller sea 
lion 
Size class 
All classes 
Large 
Unclassified 
Small 
All classes 
Large 
Unclassified 
Small 
Chum 
27.4% 
22.9% 
30.8% 
30.0% 
13.6% 
20.5% 
14.2% 
6.0% 
Chinook 
7.1% 
5.7% 
7.7% 
10.0% 
9.5% 
6.8% 
8.7% 
14.0% 
Steelhead 
3.6% 
2.9% 
2.6% 
10.0% 
10.9% 
11.4% 
14.2% 
2.0% 
Pink 
11.9% 
8.6% 
15.4% 
10.0% 
8.6% 
13.6% 
7.9% 
6.0% 
Identified 
Sockeye Unid. 
3.6% 84 
5.7% 
0.0% 
10.0% 
0.5% 
0.0% 
0.8% 
0.0% 
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