Matkin et al.: Ecotypic variation and predatory behavior among Orcinus orca off tfie eastern Aleutian Islands 



85 



served kills is therefore important to develop greater 

 confidence and detail in estimating the composition of 

 killer whale diets. 



Our seasonal bias towards spring and summer leaves 

 uncertainty about killer whale diets during fall and 

 winter. In this regard, analytical techniques that in- 

 clude identification of fatty acids, stable isotopes, and 

 contaminants may prove useful when coupled with field 

 observations to obtain a more complete picture of the 

 feeding habits of killer whales during these seasons 

 (Herman et al., 2005). 



Conclusions 



Our work underscores the importance of determining 

 lineages and ecotypes of killer whales before making 

 assumptions regarding feeding habits and potential 

 impact of killer whales on prey populations. Although 

 there may be well over 100 marine mammal-eating tran- 

 sient killer whales that aggregate in False Pass-Unimak 

 Island region to feed on gray whales in spring, the major- 

 ity of the killer whales present in summer are fish-eating 

 residents. In the summer, marine-mammal-eating tran- 

 sients are far less abundant than in spring. 



Our study indicates that the diet of transient killer 

 whales off the eastern Aleutian Islands contrasts with 

 the diets of transient killer whales in other parts of 

 the North Pacific. In British Columbia, for example, 

 transient killer whale diet is composed primarily of 

 harbor seals (Ford et al., 1998), whereas both harbor 

 seals and harbor porpoise are the primary prey of killer 

 whales in northern Glacier Bay and Icy Strait region 

 of southeastern Alaska (Matkin et al., 2005). Further 

 north, in Prince William Sound and Kenai Fjords, the 

 dominant prey of the ATI transient killer whales are 

 harbor seals and Ball's porpoises (Saulitis et al., 2000). 

 Only in the Gulf of Alaska (Kenai Fjords) has predation 

 by some Gulf of Alaska transient killer whales appar- 

 ently focused on sea lions (Matkin et al., 2005). 



Killer whale feeding behavior needs to be examined 

 on a region-by-region basis, as well as seasonally. Expe- 

 rience in other regions of the North Pacific has shown 

 that estimated population sizes, life history param- 

 eters, and dietary information can be obtained with 

 a concerted long-term research effort. Our study has 

 demonstrated that the eastern Aleutians also support 

 the presence of three killer whale ecotypes, as has been 

 previously described along the Pacific Coast of North 

 America. It also has developed minimum estimates of 

 the numbers of transient and resident killer whales that 

 use the region and has provided information that may 

 indicate that grey whales and northern fur seals are 

 important prey items in this region at certain times and 

 in certain areas. Steller sea lions were not a primary 

 prey during our spring and summer surveys. Whether 

 or not killer whales are impeding population recovery of 

 Steller sea lions in the eastern Aleutian Islands cannot 

 be answered decisively, nor can the effect that killer 

 whales may be having on other species in this region 



as yet be ascertained. Answers to these and other ques- 

 tions are expected to become clearer as the observation- 

 al database for killer whales is expanded and the data 

 for regions within the North Pacific are compared. 



Acknowledgments 



Financial support was provided by the Cooperative Insti- 

 tute for Arctic Research (CIFAR), the National Marine 

 Mammal Laboratory, the National Oceanic and Atmo- 

 spheric Administration, the Steller Sea Lion Research 

 Initiative (SSLRI), the North Pacific Universities Marine 

 Mammal Research Consortium (NPUMMRC), the North 

 Pacific Marine Science Foundation, and the Alaska 

 Sea Life Center (ASLC). Field biologists included P. 

 Nielson, T. Markowitz, D. Power, and L. Mazzuca and 

 vessel operations were directed by M. Brittain. Vessel 

 operators were B. Schauff, P. Thompson, B. Laukitis, 

 D. Graves, T. Peterson, A. Bartlett, and G. Marshall. 

 Assistance in the field was provided by L.A. Holmes, R. 

 Brewer, V. Vergara, T. Ciosek, G. Calef, C. Bianchini, 

 A. G. MacHutchon, K. Leonard, F. Nicklin, K. Walker, 

 D. Masters, and R. Blancato. Office and logistic support 

 were provided by P. Rosenbaum and J. Rose. 



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