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Three genetically and acoustically distinct, nonassociating ecotypes of killer whale (Orcinus orca) occur between southeastern Alaska and the Bering Sea: (1) residents (fish-eaters), (2) Bigg's (formerly transient; mammal-eaters), and (3) offshores (shark-eaters) (Matkin et al., 1999; Ford et al., 2011). Bigg's killer whales across this range have been genetically separated into four putative populations: (1) West Coast transients, (2) AT1 (or Chugach) transients, (3) Gulf of Alaska transients, and (4) Eastern Aleutian transients (BarrettLennard, 2000; Parsons et al., 2013). Dietary differences between these populations have been described (Ford et al., 1998; Saulitis et al., 2000; Matkin et al., 2007, 2012; Barrett-Lennard et al., 2011). Gulf of Alaska transients are known to feed upon Steller sea lions (Eumetopias jubatus), Dall's porpoises (Phocoenoides dalli), and harbor seals (Phoca vitulina) (Heise et al., 2003), while AT1 transients feed primarily on harbor seals and Dall's porpoises but not sea lions (Saulitis et al., 2000). Around Unimak Island, Eastern Aleutian transients feed seasonally on migrating gray whale (Eschrichtius robustus) calves and subadults (Barrett-Lennard et al., 2011).
Eyewitness accounts of killer whale predation on humpback whales (Megaptera novaeangliae) in the North Pacific are rare (Jefferson et al., 1991; Matkin & Saulitis, 1994; Mizroch & Rice, 2006; Reeves et al., 2006; Ford & Reeves, 2008). In a review of the literature, Ford & Reeves (2008) summarized only 15 reliably documented accounts of predatory interactions between the two species. Recently, in western Australia, Pitman et al. (2014) observed 14 kills during 22 separate attacks of killer whales on neonate humpback whales on their calving grounds; however, there were no attacks on older calves or juveniles.
During killer whale surveys in Lower Cook Inlet, Alaska (Figure 1), we observed Bigg's killer whales attacking humpback whale subadults and cow/calf pairs and examined carcasses of subadult humpback whales that exhibited evidence of killer whale predation and consumption. Herein, we report on four humpback whale attacks in Lower Cook Inlet and one off Kodiak Island, and we describe 17 partially consumed humpback whale carcasses also found in the region between 2006 and 2012.
The first killer whale attack was observed during an aerial survey off Kodiak Island in 2006, although individual identifications of killer whales could not be made. The other four attacks were observed on 8...