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



75 



Aleutian archipelago, nor was 

 much known about the extent 

 to which killer whales prey 

 on Steller sea lions and other 

 species of marine mammals in 

 these regions. 



The goals of our study were 

 1) to determine whether the 

 eastern Aleutian Islands are 

 also home to the three lineages 

 and ecotypes of killer whales 

 that have been identified else- 

 where in the northeastern Pa- 

 cific; 2) to derive estimates of 

 killer whale numbers for this 

 region; and 3) to document 

 the behaviour of killer whales 

 foraging on marine mammals. 

 Obtaining such information 

 about killer whale numbers, 

 diets, and hunting behavior is 

 critical for resolving the role 

 that killer whales may have 

 played in the decline and lack 

 of recovery of Steller sea lions 

 and other species of marine 

 mammals in western Alaska. 



Materials and methods 



Vessel survey tracklines 



Summer survey area '. Spring survey area 



False Pass 



Alaska 

 Peninsula 



BERING SEA 



Akutan 

 Unalaska island 

 Island 



54°N - 



PACIFIC OCEAN 



166°W 



I 



15 



30 



60 



Nautical Miles 



!_] Alaska 



Figure 1 



Tracks of the vessels during the surveys for killer whales {Orcinus orca) for the years 

 2001-2004. The vessels tended to return to areas that produced encounters with killer 

 whales. The spring False Pass-Unimak Island surveys are distinguished from the summer 

 Unimak Pass-Umnak Island surveys by the dashed line. 



Following the research method used to collect informa- 

 tion on killer whales in other regions (Matkin et al., 

 1999a; Ford et al., 20001, five types of data were gath- 

 ered: photo-identification pictures of individuals and 

 groups, acoustic recordings of killer whale calls, skin 

 tissue samples for genetic analysis, prey samples, and 

 accounts of predation. Additionally, we documented the 

 presence of potential marine mammal prey. Analysis of 

 these data allowed the determination of killer whale eco- 

 types and a description of killer whale feeding habits. 



Field methods 



Boat-based surveys over a wide geographic range 

 occurred during June-September 2002-2004 from 

 Unimak Pass to Samalga Pass, and surveys over a 

 relatively small range occurred in May and early June 

 2003-2004 in the False Pass-Unimak Island region. 

 Surveys in the broader region traversed 19,686 nauti- 

 cal miles and were focused in the Bering Sea within 

 twenty miles of the shoreline between Unimak Pass and 

 eastern Umnak Island (Fig. 1). The 2003-2004 False 

 Pass-Unimak surveys traversed 1970 miles in Ikatan 

 Bay and along the Pacific shore of Unimak Island. We 

 operated in areas of suspected high killer whale density 

 according to information provided by local fishermen and 

 researchers from the National Marine Mammal Labora- 

 tory (NMML) (Dahlheim, 1997) during previous transect 



surveys that covered broader regions. We modified our 

 surveys each season to cover the areas that were most 

 productive in providing killer whale encounters. 



The research was conducted from aluminum-hull fish- 

 ing vessels (powered by diesel inboard engines) ranging 

 from 10 to 14 meters in length. Survey effort varied by 

 year with a total of 372 days from 2001 to 2003 from 

 the Unimak Pass to Samalga Pass in summer and a 

 total of 49 survey days in 2003 and 2004 in the False 

 Pass-Unimak Island region in spring (Table 1). All 

 sightings of marine mammals during vessel surveys 

 were recorded and the number of individuals was esti- 

 mated to determine the relative abundance of potential 

 prey items. 



Photographs of the left side of dorsal fins and saddle 

 patches of killer whales were taken with a Nikon F-lOO 

 camera (B and H Photo, New York, NY) equipped with 

 either fixed 300-mm lenses or 100-300 zoom lenses and 

 loaded with Fuji Neopan ASA1600 black and white film 

 (B and H Photo New York, NY). These photographs were 

 checked against existing photo-catalogues of Alaskan 

 killer whales (Dahlheim, 1997; Matkin et al., 1999a) 

 and other unpublished photographs. Tissue samples 

 of at least one whale in each group were collected for 

 genetic analysis and biopsy when weather and behavior 

 of the whales permitted close approach. These samples 

 were collected by using lightweight darts and an air- 

 powered rifle (Barrett-Lennard et al., 1996). The outer 

 skin portion of the samples was used for genetic analy- 

 sis, and the underlying blubber portion was used for 



