308 
Fishery Bulletin 112(4) 
thermore, the absence of sea lion remains could be ex- 
plained by the comparably small size (1.3-2. 8 m TL) of 
the sharks sampled, if smaller sharks are less likely to 
attack larger and faster prey items. All sampled ani- 
mals were probably immature (Courtney and Sigler, 
2007). This size bias could be driven by the possible 
absence of larger sharks in the region (Hulbert et al., 
2006) or by the possible size bias of long-lining toward 
younger, smaller individuals (for remarks on landing 
and sampling likelihood for long-line gear, see Orlov 
and Moiseev, 1999; Yano et al., 2007; Courtney and 
Sigler, 2007). Courtney and Foy (2012) reported an 
increase in trophic position with TL in Pacific sleep- 
er sharks. They suggested that the diet of the Pacific 
sleeper shark probably also varies by time and location 
of capture and in response to prey availability. There- 
fore, given the evidence of ontogenetic, seasonal, and 
geographic diet shifts in many shark species, includ- 
ing the Greenland shark, southern sleeper shark, and 
Pacific sleeper shark (Orlov and Moiseev, 1999; Fisk et 
al., 2002; Yano et al., 2007; Courtney and Foy, 2012), 
the absence of sea lion tissue in the sampled sharks 
is, perhaps, not surprising and does not contradict our 
indirect evidence of predation on Steller sea lions. 
Conclusions 
Of all observed events of predation on juvenile Steller 
sea lions, at least 3 and likely 4 in 15 — or approximate- 
ly 27% — could be attributed to Pacific sleeper sharks. 
Although these observations do not constitute proof 
of attacks on live Steller sea lions by Pacific sleeper 
sharks, our data indicate that Pacific sleeper sharks 
need to be considered as a possible source of mortality 
of juvenile Steller sea lions in the region of the Gulf of 
Alaska and Prince William Sound. 
Acknowledgments 
We appreciate the assistance provided by the dive 
capture and husbandry teams of the Alaska Sea Life 
Center. Implant surgeries were conducted by M. Haule- 
na, P. Tuomi, C. Goertz, and R. Berngartt. This study 
was supported by grants from the North Pacific Ma- 
rine Research Program (00-0029), U. S. Department 
of Commerce Steller Sea Lion Research Initiative 
(NA17FX1429), North Pacific Research Board (F4011), 
and Pollock Conservation Cooperative Research Center 
(01-0047 & G5498) and by the Alaska Sea Life Center 
with the use of U. S. Department of Commerce funds. 
These funding organizations had no role in the design 
of this study, data collection and analysis, the decision 
to publish, or preparation of this manuscript. 
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