74 



Abstract— From 2001 to 2004 in the 

 eastern Aleutian Islands, Alaska, 

 killer whales (Orcinus orca) were 

 encountered 250 times during 421 

 days of surveys that covered a total 

 of 22,491 miles. Three killer whale 

 groups (resident, transient, and off- 

 shore) were identified acoustically and 

 genetically. Resident killer whales 

 were found 12 times more frequently 

 than transient killer whales, and 

 offshore killer whales were encoun- 

 tered only once. A minimum of 901 

 photographically identified resident 

 whales used the region during our 

 study. A total of 165 mammal-eating 

 transient killer whales were identi- 

 fied, and the majority (70%) were 

 encountered during spring (May and 

 June). The diet of transient killer 

 whales in spring was primarily gray 

 whales iEschrichtius robustus), and 

 in summer primarily northern fur 

 seals (Callorhinus ursinus}. Steller 

 sea lions (Eumetopias jubatus) did 

 not appear to be a preferred prey or 

 major prey item during spring and 

 summer. The majority of killer whales 

 in the eastern Aleutian Islands are 

 the resident ecotype, which does not 

 consume marine mammals. 



Ecotypic variation and predatory behavior 

 among killer whales {Orcinus orca) 

 off the eastern Aleutian Islands, Alaska 



Craig O. Matkin (contact author)' 



Lance G. Barrett-Lennard^ 



Harald Yurk^ 



David Ellifrit^ 



Andrew W. Trites'' 



Email address for C. O, Matkin: cmatkin(5iacsalaska,net 



' North Gulf Oceanic Society 

 3430 Mam St. Bl 

 Homer, Alaska 99603 



^ Vancouver Aquarium Marine Science Center 



University of British Columbia 



845 Avison Way 



Vancouver, B.C , Canada V6G 3E2 

 ^ Center for Whale Research 



355 Smugglers Cove 



Friday Harbor, Washington 98250 



" Marine Mammal Research Unit, Fisheries Centre 

 University of British Columbia 

 Vancouver, B.C., Canada V6T IZ4 



Manuscript submitted 5 December 2005 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 18 April 2006 by the Scientific Editor. 



Fish. Bull. 105;74-87 (2007). 



In 1992, flipper tags from fourteen 

 Steller sea lions (Eumetopias jubatus} 

 were found in the stomach of a killer 

 whale (Orcinus orca) that had died 

 in Prince William Sound (Heise et 

 al., 2003). This discovery prompted 

 considerable interest and specula- 

 tion about the role that killer whales 

 may have played in the decline and 

 lack of recovery of Steller sea lions 

 in western Alaska (Barrett-Lennard 

 et al., 1995). Since the late 1970s, 

 Steller sea lions in the Gulf of Alaska 

 and Aleutian Islands have declined 

 by over 80% (Merrick et al., 1987; 

 Trites and Larkin, 1996; Loughlin 

 and York, 2000; Winship and Trites, 

 2006). Similar sharp declines have 

 also occurred among some popula- 

 tions of harbor seals (Phoca vitulitia), 

 northern fur seals (Callorhinus ursi- 

 nus), and sea otters (Enhydra lutris) 

 (York, 1987; Pitcher, 1990; Trites, 

 1992; Estes et al., 1998). Whether 

 or not these declines are related to 

 killer whales is currently the sub- 

 ject of considerable scientific debate 

 (Springer et al., 2003; Trites et al.. 



2006; DeMaster et al., 2006; Mizroch 

 and Rice, 2006 ). 



Most knowledge about killer 

 whales in the North Pacific has been 

 gathered between California and 

 the northern Gulf of Alaska, where 

 three distinct lineages of killer 

 whales have been identified: fish-eat- 

 ing "resident" killer whales, which 

 appear predictably in large groups 

 from Washington to Alaska; marine 

 mammal-eating "transient" killer 

 whales, which appear infrequently 

 and in smaller groups; and "offshore" 

 killer whales, whose feeding habits 

 are poorly known, but are thought 

 to eat fish, including sharks (Mat- 

 kin et al., 1999a; Barrett-Lennard, 

 2000; Ford et al., 2000; Saulitis et 

 al., 2000). These groups are geneti- 

 cally and behaviorally distinct, but 

 have overlapping geographic ranges 

 and are considered as ecotypes be- 

 cause of their differences in diet. 

 However, prior to our study, it was 

 not known whether these lineage and 

 ecotype distinctions extended to the 

 northwestern Gulf of Alaska and the 



