Scordino et al.: Dietary niche overlap and prey consumption for Eumetopias jubatus and Zalophus californianus Al 
124°50'W =: 124°40'W 
Carmanah Poin 
oe Tatoosh Island 
Complex ° 
rere 
Bodelteh Islahd 
Complex 
48°10'N 
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9 
= 
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9 
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3 
48°0'N4 Carroll Island 
Sea Lion Rock®”. ° 
124°30'W 
Washington 
124°20'W Ss 124° 10'W 124°0'W 
(@) Haul-out sites 
@ Cities 
200-m isobath 
Pa 
_Waadah Island ©°7 
120°0'W. 
Canada 
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Seattle:e | 
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45°0'N Portland ® 
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35°0'N 
Figure 1 
Map of study area of northwest Washington marking haul-out sites of Steller sea lions 
(Eumetopias jubatus) and California sea lions (Zalophus californianus) where counts of 
sea lions and scat collections occurred from 2010 through 2013. The dotted line indicates 
the 200-m isobath. 
Counts of the age-1+ population were included in this 
analysis only if sea lions at all the haul-out sites in the 
survey area were counted and, for Steller sea lions, only 
if a full demographic count was conducted. The excep- 
tion was that if we had a land-based count for East 
Bodelteh Island within 10 d of a survey that included 
all haul-out sites, we used the land-based count for East 
Bodelteh Island rather than the boat-based count for 
that day. The counts are minimum estimates of sea lions 
present because an unknown proportion of the sea lions 
that were hauled out were not visible during the sur- 
veys and, therefore, were not counted (Westlake et al., 
1997). We used average counts, rather than maximums, 
because both species of sea lions are known to change 
their distribution in response to prey and other factors 
(Sigler et al., 2009; Womble et al., 2009; Olesiuk*; Brown 
et al., 2020). 
Scat collection We collected scat from the Tatoosh Island 
Complex, Bodelteh Islands Complex, Carroll Island, and Sea 
Lion Rock (Fig. 1). Locations of scat collections differed by 
season and were influenced by sea conditions, safety of trans- 
ferring staff onto the haul-out site, and haul-out utilization by 
sea lions. Samples of scat of California sea lions were primar- 
ily collected at East Bodelteh Island, where large aggrega- 
tions of California sea lions occur in the spring, early summer, 
and fall. A central assumption to our sampling method was 
that scat collected from any haul-out site in northwest Wash- 
ington was representative of scat of Steller and California sea 
lions at all haul-out sites in northwest Washington. 
