154 
Fishery Bulletin 110(2) 
dation pressure by an increased number of transient 
killer whales. 
It might be expected that the combination of re- 
duced numbers of ATI transient whales, the apparent 
rebound of harbor seals in the region, and a recent 
increase in Steller sea lion numbers, particularly in 
the eastern Gulf of Alaska (Allen and Angliss, 2010), 
would lead to increased use of these coastal waters by 
GOA transients. Because the local extinction of a killer 
whale population, as is likely for the ATI population, 
is an unprecedented event, it is unknown whether 
members of the GOA population eventually will ex- 
pand their use of the region. Our analysis indicates 
that, despite greatly reduced ATI transient numbers 
and a slowly increasing prey population, this has not 
yet occurred. 
Conclusion 
This study illustrates the importance of examining dif- 
fering population trends and movements of individual 
killer whale ecotypes to reveal subtleties of population 
ecology and potential prey impacts. The Kenai Fjords- 
Prince William Sound region at the northern Gulf of 
Alaska supports two distinct non-associating transient 
populations that both occur at low numbers relative to 
other well-studied North Pacific regions. Despite their 
common position at the apex of marine food chains, each 
population exerts unique ecological impacts based on 
food preferences, prey abundance, and habitat use. These 
diverse impacts are reflected in the different range and 
trajectories of our study populations. The ATI transients 
are a localized, inshore population apparently headed 
for extinction, whereas the GOA transients are a wider 
ranging, more oceanic population with relatively stable 
numbers. 
Our study reveals that for small, infrequently ob- 
served populations such as the GOA transients, mark- 
recapture methods can be coupled with a Bayesian 
statistical approach to quantify important population 
parameters and examine population trends. With a com- 
bination of extensive geographically based photographic 
data and satellite tracking results, we can begin to 
define important aspects of population ecology. 
Acknowledgments 
The majority of the long-term funds for the project were 
provided by the Exxon Valdez Oil Spill Trustee Council 
and the Alaska SeaLife Center. The Norcross Wild- 
life Foundation provided equipment. Hubbs Seaworld 
Research Institute and the National Marine Mammal 
Laboratory funded early work. Dozens of individuals 
have made substantial contributions to this multidecadal 
project. We are indebted to all of you. We would like to 
thank O. von Ziegesar, C. St. Amand, L. A. Holmes, L. 
Mazzuca, D. Maldini, and D. Olsen for data contribu- 
tions. A. Gaylord assisted with GIS analysis. W T . Perrin 
and three reviewers made invaluable comments on the 
manuscript. 
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