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Fishery Bulletin 120(2) 
Table 5 
Comparison of average commercial landings of salmon to salmon consumption by California sea lions 
(Zalophus californianus), Steller sea lions (Eumetopias jubatus), and both species combined, by species, 
from 2010 through 2013 in northwest Washington. Sea lion consumption estimates are reported sepa- 
rately for all and large (250 cm in total length) size classes because only large salmon are targeted by 
commercial fisheries. Estimates of consumption by California sea lions are partial-year estimates that do 
not include consumption in winter. 
Commercial landings 
Coastal All of All 
classes 
Species Washington Washington 
Chinook 406.7 2421.0 
Chum 143.5 4819.4 
Coho 1646.8 
Pink f 4911.5 
Sockeye j 1646.6 
Steelhead : 169.7 
studies indicate that pinnipeds typically eat fish less than 
30 cm in length (Etnier and Fowler, 2010) and that pink 
salmon are the smallest Pacific salmon. 
California and Steller sea lions ate over 2550 t of Pacific 
salmon per year during 2010-2013 in northwest Wash- 
ington; therefore, it is logical to examine whether these 
2 species of sea lions are affecting the species of Pacific 
salmon listed under the ESA. The Fishery Regulation 
Assessment Model is used to model stock-based effects of 
fisheries on coho and Chinook salmon on the basis of data 
from recovery of coded-wire tags (Moran et al., 2018). We 
ran the Fishery Regulation Assessment Model by using 
data for marine fishing management areas 3, 4, and 4B, 
areas designated by the Washington Department of Fish 
and Wildlife that include Carroll Island, Sea Lion Rock, 
the Tatoosh Island Complex, the Bodelteh Island Com- 
plex, and Waadah Island (Fig. 1). We used these data from 
these areas in 2010-2013 to determine what proportion of 
the large Chinook and coho salmon consumed by sea lions 
were likely to be from populations listed as threatened or 
endangered under the ESA. We assumed for the purpose 
of this model that California and Steller sea lions eat a 
composition of stocks of coho and Chinook salmon similar 
to the stock composition of Pacific salmon caught in fisher- 
ies. We found that roughly 3% of the large coho salmon and 
5% of the large Chinook salmon in marine fishing man- 
agement areas 3, 4, and 4B during 2010-2013 were from 
ESA-listed populations. 
The effect of predation by California and Steller sea lions 
on ESA-listed populations of Chinook salmon is likely less 
than the effect of commercial fisheries given the disparity 
in the metric tons of Chinook salmon landed by the fisher- 
ies and the metric tons consumed by California and Steller 
sea lions (Table 5). In contrast, the effect of predation by 
California and Steller sea lions on ESA-listed populations 
of coho salmon likely exceeds the effect of commercial 
Steller 
Sea lions in northwest Washington 
California Both species 
Large All Large All Large 
class classes class classes class 
80.9 33.2 197.3 47.4 
316.4 97.5 587.5 185.0 
601.0 336.5 1462.8 493.9 
125.2 31.9 241.6 58.4 
40.7 29.8 47.9 29.8 
23.4 9.2 180.5 31.4 
fisheries for the reasons previously discussed. California 
and Steller sea lions may also be affecting the recovery of 
the threatened population of Lake Ozette sockeye salmon 
given its small size of 7000 returning adults during 2016— 
2019 (Haggerty’) and the proximity of the outfall of the 
Ozette River to the haul-out sites we surveyed. Ecosystem 
modeling that incorporates the direct effect of predation 
by sea lions on salmon as well as the effects on salmon 
predators and prey should be conducted to investigate the 
effect of California and Steller sea lions on populations of 
salmon in the Pacific Northwest. 
A goal of this study was to evaluate if California and 
Steller sea lions in northwest Washington compete with 
endangered southern resident killer whales for their pre- 
ferred prey of large Chinook salmon (Ford and Ellis, 2006; 
Hanson et al., 2021). We found that large Chinook salmon 
accounted for at least 0.3% and 0.1% of the diets of Califor- 
nia and Steller sea lions, respectively. The small amount of 
large Chinook salmon consumed by California and Steller 
sea lions relative to the catch in sport and commercial fish- 
eries in northwest Washington (Table 5) indicates that, in 
our study area, both species of sea lions are not major direct 
competitors with killer whales for prey. California and 
Steller sea lions likely have indirect effects on the availabil- 
ity of prey of killer whales because their predation on small- 
and medium-sized Chinook salmon reduces the number of 
Chinook salmon reaching the large size preferred by killer 
whales. The magnitude of this indirect effect is hard to eval- 
uate because estimates of the number of Chinook salmon 
eaten are very sensitive to the estimated size of Chinook 
salmon consumed (Chasco et al., 2017a, 2017b; Nelson et al., 
2021). Our size sorting allowed us to make broad interpre- 
tations of the size classes of Pacific salmon predated by 
° Haggerty, M. 2022. Personal commun. Mike Haggerty Consulting, 
242 Whiskey Creek Beach Rd., Port Angeles, WA 98363. 
