Scordino et al.: Consumption of Oncorhynchus spp. by Zalophus californianus and Eumetopias jubatus in Washington 
Table 4 
Estimated average seasonal consumption of salmon in metric tons (t) by Steller (Humetopias jubatus) and California (Zalophus 
californianus) sea lions, by size class of prey and season during 2010—2013 in northwest Washington. Species of salmon were 
identified by analyzing bones found in sea lion scat. The size classes are small (<25 cm in total length [TL]), large (=50 cm TL), 
and unclassified. The total consumption estimates for California sea lions are partial-year estimates from spring through fall 
(no scat of California sea lions was collected in winter). Consumption of the family Salmonidae is informed by the split-sample 
frequency of occurrence (SSFO) of prey taxa. The consumption of individual salmon species within size classes is informed 
by the SSFO of prey identified to the lowest possible taxon, with species of different size classes treated as unique species. As 
a result, the estimated total consumption of individual species does not equal the total estimated consumption of the family 
Salmonidae. 
Consumption by Steller sea lions (t) 
Taxon Spring Summer Fall 
Salmon (Salmonidae) 377.1 
Small size class 
Coho salmon 
Chum salmon 
Chinook salmon 
Steelhead 
Pink salmon 
Sockeye salmon 
Unidentified 
Unclassified 
Coho salmon 
Chum salmon 
Chinook salmon 
Steelhead 
Pink salmon 
Sockeye salmon 
Unidentified 
Large size class 
Coho salmon 
Chum salmon 
Chinook salmon 
Steelhead 
Pink salmon 
Sockeye salmon 
Unidentified 
commercial fisheries throughout the state of Washington. 
Roughly half of the population of Steller sea lions in 
Washington State haul out in our study area (Scordino 
et al.*). Furthermore, the positive trend in counts at haul- 
out sites in northwest Washington (Allyn and Scordino, 
2020) indicates that the abundance of California and 
Steller sea lions has more than doubled over the past 
decade, and their consumption of Pacific salmon has likely 
also doubled. Therefore, the total mass of coho salmon con- 
sumed by California and Steller sea lions in all of Wash- 
ington is likely much greater than is landed in commercial 
* Scordino, J. J., S. J. Jeffries, and B. A. Diehl. 2014. Steller sea 
lion aerial survey counts in Washington, Oregon, and north- 
ern California during the breeding season of 2011. In Research 
and education/outreach to benefit ESA listed and recently del- 
isted marine mammals of northwest Washington (J. J. Scordino 
and A. M. Akmajian, eds.), p. 190-198. Final report for species 
recovery grant award NA10ONMF4720372. [Available from Makah 
Fish. Manag., Makah Tribe, P.O. Box 115, Neah Bay, WA 98357.] 
Winter 
Consumption by California sea lions (t) 
Annual Spring Summer Fall Spring-—fall 
1204.8 
fisheries. Future efforts to model marine survival of coho 
salmon would benefit from inclusion of the abundance of 
California and Steller sea lions. 
Prior to conducting our study, we hypothesized that 
consumption of Pacific salmon by California and Steller 
sea lions would be greatest during the summer of odd- 
numbered years, when large runs of pink salmon are 
available. Contrary to that expectation, the season with 
the lowest overall salmon consumption by Steller sea lions 
was summer, when many adult Pacific salmon, including 
pink salmon, migrate through the study area. Further- 
more, Pacific salmon accounted for a smaller component 
of the diets of both California and Steller sea lions in 2011 
than in 2012. Pink salmon were the most commonly con- 
sumed salmon by Steller sea lions during the summer, 
but not by as much as expected given that, during 2011, 
roughly 70% of the Pacific salmon returning to Puget 
Sound were pink salmon (Losee et al., 2019). This result is 
even more surprising given that results from previous diet 
