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of scat collected per trip ranged from 2 to 78 (mean of 
34) (Table 1). Of the 1416 scat, 22 were discarded from 
analysis because they had no prey and 11 were discarded 
because they contained only unidentified prey, resulting 
in a working data set of 1383 scat. The majority of sam- 
ples came from Rogue Reef during the breeding (n=526) 
and nonbreeding («=290) seasons, followed by collec- 
tions at the Columbia River South Jetty (n=219) and St. 
George Reef (n = 165) during the breeding season. Only 
minor collections were made at Orford Reef during the 
breeding season 0? = 56), and Cascade Head (n=24) and 
St. George Reef (n- 7) during the nonbreeding season 
(Table 1). 
A total of 47 Steller sea lion prey taxa from 30 families 
were identified (33 to species) (Table 2). Overall percent 
frequency of occurrence for the most common (FO>10%) 
prey in decreasing order were Pacific hake ( Merluccius 
productus, FO=78.6%), salmonids ( Oncorhynchus spp.; 
FO = 28.6%), skates (Rajidae; FO=23.4%), Pacific lam- 
prey ( Lampetra tridentata; FO=20.8%), clupeids (Clu- 
peidae; FO=18.7%), rockfish (Sebastes spp.; FO=17.4%), 
northern anchovy ( Engraulis mordax ; FO=13.2%), and 
unidentified teleost fishes (FO = 10.8%) (Table 2, Fig. 
2). Scat during the breeding season were dominated 
by hake (87.1%), followed by salmonids (27.1%) and 
Pacific lamprey at 20.1%. Hake, with an FO of 59%, 
was also a primary prey in samples collected during 
the nonbreeding season and skate species increased in 
frequency to 40.3%, followed by salmonids (32.1%), and 
rockfish (29.7%) (Table 2). Prey diversity within scat 
samples ranged from one to 25 types, although 64% of 
all samples had <3 prey types. Of the 222 scat collected 
during the breeding season that contained a single prey 
item, 85.1% contained Pacific hake and 4.1% contained 
rockfish. Scat collected during the nonbreeding season 
that contained a single prey species (n = 63), 49.2% con- 
tained hake and 22.2% rockfish. 
By site and season (Fig. 2), Pacific hake occurred in 
more scats than any other prey taxa among all sites 
and seasons except at Cascade Head and St. George 
Reef during the nonbreeding season. For example. Pa- 
cific hake was the dominant prey in scats collected at 
Rogue Reef, the largest rookery in the study area, both 
during breeding (87.3%) and nonbreeding (62.1%) sea- 
sons. Although salmonids occurred with high frequency 
at all sites and seasons, except at Cascade Head, the 
highest frequency was found at Rogue Reef during the 
nonbreeding season. Skates, although consumed at all 
sites and seasons, occurred most frequently in scats 
collected during the nonbreeding season. For example, 
skate FO increased at Rogue Reef from 16.2% to 45.5% 
during the breeding and nonbreeding seasons, respec- 
tively. Pacific staghorn sculpin ( Leptocottus armatus ) 
was common only at the northern sites (i.e., Colum- 
bia River and Cascade Head), whereas rockfish were 
common only at the southern sites (particularly Rogue 
Reef). 
In general, diet composition varied seasonally, annu- 
ally, and spatially. After controlling for site and year 
(10 of 11 comparisons; Table 3), we found that diet dif- 
fered by month; after controlling for site and month, we 
found that diet differed by year (10 of 12 comparisons; 
Table 4); and after controlling for year and month (2 of 
3 comparisons; Table 5), we found that diet differed by 
site. Average Jaccard distance within collections ranged 
from 0.206 to 0.807 (median of 0.724), whereas average 
Jaccard distance between collections ranged from 0.425 
to 0.911 (median of 0.771). 
Discussion 
Like other researchers (e.g., Pitcher, 1981; Merrick et al., 
1997; Sinclair and Zeppelin, 2002; Womble and Sigler, 
2006; Trites et al., 2007b; McKenzie and Wynne, 2008), 
we found that Steller sea lion diet was diverse yet domi- 
nated by only one or two species (Fig. 3). In Oregon and 
northern California the diet was dominated by Pacific 
hake, whereas in Alaska diet was dominated by walleye 
pollock (Theragra chalcogramma) in the Bering Sea and 
Gulf of Alaska, and Atka mackerel ( Pleurogrammus 
monoptery gius) in the Aleutians Islands. Prey types 
shared between Alaskan and Oregon-northern Califor- 
nia collections included salmonids, clupeids (e.g., Pacific 
herring [Clupea pallasii]), rockfish, and skate. 
The dominance of Pacific hake in Steller sea lion 
diets in Oregon and northern California is probably 
related to the widespread abundance of this species 
in the California current (as is the case with the 
widespread distribution of walleye pollock in Alas- 
kan waters). Dorn et al. 2 reported that Pacific hake, 
ranging from southern California to the Queen Char- 
lotte Sound, British Columbia, was the most abundant 
groundfish in the California Current system. During 
summer months adult Pacific hake move north along 
the Oregon coast while juveniles stay further south 
off central California (Bailey et al., 1982). From 1966 
to 2007 the Pacific Coast (U.S, and Canadian waters) 
Pacific hake fishery landings averaged 219,000 metric 
tons (t), with a low of 90,000 t in 1980 and a peak har- 
vest of 364,000 t in 2006 (Helser et al., 2008). Pacific 
hake are similar in caloric density to cod and pollock, 
which are prominent in the diet of Steller sea lions in 
the WDPS. This gadid diet has been hypothesized to 
result in chronic nutritional stress and ultimately pop- 
ulation declines (Trites and Donnelly, 2003, Trites et 
al., 2007a). However, despite the dominance of Pacific 
hake in the diet from Oregon and northern California, 
Steller sea lions in the EDPS have been increasing at 
approximately 3% per year since the 1970s (Pitcher et 
al., 2007). This fact was cited by Fritz and Hinckley 
(2005) as evidence that was inconsistent with the nu- 
tritional stress hypothesis. 
2 Dorn, M. W., M. W. Saunders, C. D. Wilson, M. A. Guttormsen, 
K. Cooke, R. Kieser, and M. E. Wilkins. 1999. Status of 
the coastal Pacific hake/whiting stock in U.S. and Canada 
in 1998, 102 p. [Available at Pacific Fishery Management 
Council, 7700 NE Ambassador Place, Suite 101, Portland, 
OR. 97220 1384.] 
