Riemer et al. : Food habits of Eumetopias /ubatus off Oregon and northern California, 1986-2007 
379 
particularly on the southern part of the species range, 
warranted continued research and monitoring. Popu- 
lation growth in California sea lions (Carretta et al., 
2010) may also be a concern for the EDPS because 
these sympatric ottariids potentially compete for prey 
resources and habitat. Steller sea lions in the Channel 
Island rookeries in California experienced a similar 
situation in the late 1950s as California sea lion popu- 
lations increased and potentially out-competed Steller 
sea lions for food and habitat (Bartholomew and Booloo- 
tian, 1960). Additionally, as the Steller sea lion EDPS 
increases, its real and perceived impacts on sport and 
commercial fish harvests; as well as threatened and 
endangered fish populations, will likely increase. For 
example, Steller sea lion abundance at Bonneville Dam 
on the Columbia River (Fig. 1), 235 km from the ocean, 
increased from zero individuals in 2002 to at least 53 
in 2010 and these sea lions have consumed hundreds of 
threatened and endangered salmonids and thousands 
of white sturgeon (Acipenser transmontanus ) (Stansell 
et al. 4 ). Ongoing uncertainties over the role of diet in 
the decline of the WDPS, impacts of climate change 
on the EDPS, and emerging management concerns all 
argue for continued and refined research on Steller sea 
lion diet and foraging behavior in the southern extent 
of their range. 
Conclusions 
Identification of prey from 1383 Steller sea lions scats 
collected in Oregon and northern California during 
1986-2007 resulted in a list of 47 prey taxa consumed. 
Primary prey items included Pacific hake, Pacific salmon, 
skate, Pacific lamprey, rockfish and clupeid species. Prey 
identified from scat during the breeding and nonbreed- 
ing seasons were fairly similar but rockfish and skate 
species had a higher frequency of occurrence during the 
nonbreeding season. Data analysis showed that, in gen- 
eral, diet composition varied seasonally, annually, and 
spatially. When compared to previous diet studies for 
Steller sea lions in Alaska, this population was shown 
to depend on hake as the primary prey rather than on 
the gadid and hexagrammid species identified in the 
northern populations studied. Salmonids were impor- 
tant prey in all the studies compared. Continued study 
of Steller sea lion food habits is necessary to evaluate 
their interactions with important fish populations (such 
as salmonids and rockfish), to assess the increasing pres- 
sure from migrating California sea lions for limited prey 
resources, and to begin to address the effects of climate 
change on population abundance. 
4 Stansell, R. J, K. M. Gibbons, and W. T. Nagy. 2010. Evalu- 
ation of pinniped predation on adult salmonids and other fish 
in the Bonneville Dam tailrace, 2008-2010. U.S. Army Corps 
of Engineers, Cascade Locks, OR. [Available online at http:// 
www.nwd-wc.usace.army.mil/tmt/documents/fish/2010/2008- 
2010_Pinniped_Report.pdf, accessed 2 March 2011.] 
Acknowledgments 
This article summarizes over 25 years of research on 
Steller sea lions in Oregon that would not have been 
accomplished without the help of many individuals and 
agencies. We would like to thank the following for sup- 
port, guidance, and assistance: Oregon Department of 
Fish and Wildlife, National Marine Fisheries Service (J. 
Scordino, P. Gearin, R. DeLong), U.S. Fish and Wild- 
life Service Oregon Coast National Wildlife Refuge (P. 
Sekora, R. Lowe, D. Pitkin), M. Tennis, J. Jenniges, J. 
Scordino, M. Dhruv, A. Ougzin, S. Jeffries, J. Harvey, 
J. Stein, and many others who assisted in the field with 
collection of data and samples over the years. R. Emmett, 
P. Gearin, D. Fox, and R. Stauff and three anonymous 
reviewers provided beneficial comments on the man- 
uscript. This research was conducted under Marine 
Mammal Protection Act scientific research permit num- 
bers 499, 835, 854, 782-1446, 434-1669, and 434-1892. 
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