Based on several lines of evidence, Estes et al. (1998) concluded that killer whale (Orcinus orca) predation was the most parsimonious explanation for this decline. Garshelis and Johnson (1999) commented that equally compelling evidence Pictilisib for killer whale predation on otters existed for Knight Island. Common to both Knight Island and the Aleutians, there was no indication of reduced birthing or pup survival, few dead otters washed ashore (as they would in cases of disease, malnutrition, winter mortality,

or contamination), and body condition of otters indicated that food supplies were adequate ( Dean et al., 2000, Dean et al., 2002 and Laidre et al., 2006). In the Aleutians, only six killer whale attacks have been observed, and among these only three of the otters died (Hatfield et al., 1998). However, given the low probability of actually witnessing such brief events in this huge area, the three confirmed mortalities were extrapolated to an estimated 40,000 otters consumed by killer click here whales (Estes et al., 1998). It is now widely believed that killer whale predation reduced the Aleutian Islands’ otter population by more than 95% (Estes et al., 2005). Doroff et al. (2003, p. 55) called it “one of the most widespread and precipitous population declines for a mammalian carnivore in recorded history.”

Despite the rather scant observational evidence of the cause for this decline, when southwestern Alaska sea otters were proposed as a threatened population under the U.S. Endangered Species Act, killer whale predation was considered the most probable cause, with little support for other alternatives (U.S. Federal Register, 2004). Although intensive studies of both otters and killer whales have been conducted in PWS since

the early 1980s, the first attack was not witnessed until 1992 – by coincidence, shortly after the spill. All three observed killer whale attacks since then occurred at Knight Island, two of which were in Herring Bay, NKI (Hatfield et al., 1998). Additionally, in 2003, a killer whale was found dead in LaTouche Passage, south of Knight Island, with five sea otters in its stomach. This whale was identified as part of a pod whose range was centered in the Knight Island area (Vos et al., 2006). Killer whales could not only consume Leukotriene-A4 hydrolase several otters per day at Knight Island, but the risk of predation could drive otters to move to safer areas. Many scientists have moved beyond the question of whether killer whales began preying heavily on sea otters to why they did. Leading theories suggest that those killer whales that preferentially prey on marine mammals (rather than fish) have been forced to switch from diminishing stocks of harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus) to much smaller, less-preferred sea otters. Although harbor seals are a preferred prey of most marine-mammal eating killer whales, in PWS whales prey equally on Dall’s porpoise (Phocoenoides dalli).