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



83 



eastern Aleutian Islands. All killer whales examined by 

 acoustic or genetic analysis could be placed unequivo- 

 cally in the resident, transient, or offshore lineage. 



Resident killer whales 



A vast majority of the whales observed in the eastern 

 Aleutians during summer were determined to be of the 

 resident ecotype. Our minimum estimate of 901 whales 

 is as high as any density of resident killer whales in 

 any region of the eastern North Pacific studied to date 

 (Matkin et al., 1999a; Ford et al., 2000). 



Our data indicate that the eastern Aleutian resi- 

 dent killer whales comprise a distinct population, but 

 evidence is equivocal at this time. No repeated asso- 

 ciations have been recorded between eastern Aleutian 

 residents and those photographed off Kodiak Island 

 north and eastward, despite extensive field effort and 

 examination of photographic databases for matches. 

 However, at least one group of resident killer whales 

 has been photographed in both regions (Durban-j. 

 Acoustic analysis indicates that resident whales sam- 

 pled in the eastern Aleutians have call repertoires 

 distinct from other well-known resident populations de- 

 scribed from Kenai Fjords through Washington State. 

 However, on the basis of structural similarities among 

 calls from these regions, it can not be ruled out that 

 some social contact occurs or that these whales share 

 a recent common ancestry. The structure of some call 

 syllables appears to change quickly in a climate of di- 

 minishing social contact (Deecke et al., 2000), whereas 

 the overall syllable type and the syntax of syllables in 

 calls remains stable for a longer period of time (Ford, 

 1991; Yurk, 2005). Genetic samples taken in the east- 

 ern Aleutians revealed only the NR haplotype, whereas 

 those from Kodiak Island waters and in Kenai Fjords 

 yielded a mixture of NR and southern resident hap- 

 lotypes (SR haplotypes) (Barrett-Lennard, 2000). An 

 examination of nuclear alleles is needed to clarify the 

 relationship between eastern Aleutian residents and 

 other resident killer whales in other regions of the 

 North Pacific. 



Offshore killer whales 



Only one group of whales was determined to be of the 

 offshore ecotype, with 54 individuals identified in a 

 single encounter. Most (44) of the individuals identified 

 in that encounter had been identified in other regions, 

 including southern British Columbia and Kenai Fjords. 

 Alaska, indicating that there is a single wide-ranging 

 population in the eastern North Pacific. This ecotype is 

 not known to consume marine mammals and the only 

 reported stomach contents are salmonid bones, crab 

 shell, sculpin, and eelgrass (Heise et al., 2003). 



Transient killer whales 



Transient killer whales, as determined in our analyses, 

 were the only whales observed consuming marine mam- 

 mals and were not seen feeding on fish or engaging in 

 behaviors associated with fish-feeding in other areas 

 (Ford and Ellis, 1999; Saulitis et al., 2000 ). This obser- 

 vation supports findings in other regions that indicate 

 transient killer whales are a distinct ecotype specializ- 

 ing in marine mammal prey and comprise a subset of the 

 total whales found in any region (Matkin et al., 1999b; 

 Ford et al., 2000). Most of the 165 transient individu- 

 als identified in our study were present only in spring 

 and early summer when gray whales were migrating. 

 We documented only 51 different transient individuals 

 in late summer, at which time their appearance was 

 sporadic and they seemed to leave the region for periods 

 of weeks or longer. 



Transient killer whales in the eastern Aleutians 

 display a unique call repertoire that is distinct from 

 from the repertoire of transient killer whales in other 

 regions. Therefore, the eastern Aleutian group may rep- 

 resent a separate population. Other than three whales 

 photographed near the Barren Islands by NMML in 

 2001 (Durban-), and resighted east of Unalaska Island 

 in 2002; no other transient whales from this area have 

 been photographed north and east of the Shumagin 

 Islands. The results of mitochondrial DNA analysis are 

 equivocal because the three haplotypes we identified all 

 occur in waters of the northern Gulf of Alaska. Again, 

 extensive examination of nuclear alleles and comparison 

 with those from other regions will be needed to clarify 

 population structure. 



For example, more detailed genetic analysis of eastern 

 Aleutian transient killer whales exhibiting the ATI 

 haplotype has shown that they have dissimilar nuclear 

 alleles from those of the threatened ATI population of 

 Prince William Sound and Kenai Fjords (Barrett-Len- 

 nard'^). This finding indicates that the similarity of their 

 haplotypes reflects historical lineage sorting rather 

 than a recent descent from a common maternal ances- 

 tor. Because haplotypes reflect maternal lineages, the 

 co-occurrence of two haplotypes in the transient whale 

 aggregations encountered in the False Pass-Unimak 

 Island area during spring supports the idea that dis- 

 tinct matrilines that may not associate at other times 

 of year join to form these aggregations. 



The small overlap (3.6% of the individuals) between 

 transient killer whales encountered west of Unimak 

 Pass in summer and transient killer whales observed in 

 spring in the False Pass-Unimak Islands area indicates 

 there is further seasonal and spatial structuring in the 

 population. The large percentage of new transient killer 

 whales encountered in each year of summer studies, 

 compared to the lower percentage of resighted individu- 



^ Durban, J. 2005. Unpubl. data. National Marine Mammal 

 Lab, National Marine Fisheries Service, 7600 Sand Point 

 Way NE, Seattle, WA 98115. 



^ Barrett-Lennard L. 2005. Unpubl. data. Vancouver 

 Aquarium, 845 Aviso Rd. Vancouver, BC, Canada.V6G 

 3E2 



