50 
Fishery Bulletin 120(1) 
Table 4 (continued) 
Total 
Prey group SSFO 
Eelpouts: family Zoarcidae 0.4% 
Eelpouts, unidentified 0.4% 
Sand lances: family Ammodytidae 0.2% 
Pacific sand lance (Ammodytes hexapterus) 0.2% 
Lampreys: family Petromyzontidae 0.2% 
Pacific lamprey (Entosphenus tridentatus) 0.2% 
Jacks: family Carangidae 0.2% 
Jack mackerel (Trachurus symmetricus) 0.1% 
Sculpins: family Cottidae 0.1% 
Sculpins, unidentified 0.1% 
Snailfishes: family Liparidae 0.1% 
Snailfishes, unidentified 0.1% 
Hagfishes: family Myxinidae 0.1% 
Pacific hagfish (Eptatretus stoutii) 0.1% 
pinniped studies (Womble et al., 2009; Walters et al., 
2020). The diet of California sea lions generally met our 
expectation; whereas, the portion of Salmonidae in the 
diet of Steller sea lions was smaller in summer than in 
winter by a factor of 3. 
Annual variability in the diets of both sea lion species 
were also observed. Large annual differences in the por- 
tion of the diet composed of Pacific sardine and Pacific 
hake were likely driven by environmental factors that 
affect their distribution (Demer et al., 2012; Malick et al., 
2020). We had expected to see a large increase of Salmoni- 
dae in the diet of both sea lion species during 2011 because 
—_ 
Oo 
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j=) 
© Steller sea lions 
1 California sea lions 
Average metric tons consumed 
Spring Summer Fall Winter 
Figure 4 
Estimated metric tons of prey consumed by Steller (Hume- 
topias jubatus) and California (Zalophus californianus) 
sea lions per season during 2010-2013 in northwest Wash- 
ington. Error bars indicate standard deviations. 
Summer 
SSFO 
0.0% 
0.0% 
1.2% 
1.2% 
0.0% 
0.0% 
0.0% 
0.0% 
0.0% 
0.0% 
0.0% 
0.0% 
0.4% 
0.3% 
of the presence of odd-year pink salmon (Oncorhynchus 
gorbuscha), which contributed to the roughly 6 times more 
Salmonidae fish entering Puget Sound in 2011 than in 
2012 (Losee et al., 2019). Despite higher availability of 
Salmonidae in 2011, the portion of diet composed of Sal- 
monidae was slightly higher in 2012 than in 2011 for both 
sea lion species. 
Pacific hake composed a smaller portion of the sea lion 
diets than expected. From their studies of California and 
Steller sea lion diets in Washington in the 1990s, Scordino” 
and Wiles (2015) reported that bones of Pacific hake had 
an FO of 89.0-98.0%, compared with an FO of 15.0% for 
Steller sea lions and an FO of 30.6% for California sea 
lion in our study (Suppl. Table 1) (online only). The large 
decrease over time in importance of Pacific hake in the 
diet of Steller sea lions was likely due to environmental 
factors that resulted in a smaller portion of the population 
of Pacific hake utilizing northwest Washington during our 
study (Malick et al., 2020). During 2010-2013, the period 
of our study, the Makah Tribe’s commercial Pacific hake 
fishery, which is spatially restricted to northwest Wash- 
ington within 40 nmi (74 km) of shore, also had lower than 
normal landings (Svec’). Low availability of Pacific hake 
likely resulted in greater consumption by both Steller and 
California sea lions of prey that are species of conserva- 
tion concern, such as rockfish and salmon species. 
Biases in our study method may have resulted in 
inaccuracies in our diet estimations. The annual and 
seasonal variability in diet may be an artifact of our 
sampling effort (Trites and Joy, 2005). We often had only 
1 or 2 sampling occasions per season for California sea 
lions and between 1 and 6 sampling occasions per season 
for Steller sea lions, and this effort may have resulted 
in detecting short-term shifts in fish distributions and 
7 Svec, R. 2021. Personal commun. Makah Fish. Manage., Makah 
Tribe, 150 Resort Dr., Neah Bay, WA 98357. 
