Trans-Pacific Consumption of Cephalopods by North Pacific Killer Whales (Orcinus orca)

摘要

Cephalopods are an important component of many cetacean diets. Although some odontocete species in the subfamily, which includes killer whales, primarily consume squid (e.g., pilot whales, beaked whales), killer whales, for the most part, are thought to specialize. In the North Pacific Ocean, three ecotypes have been identified based on dietary specialization. These ecotypes include residents, which have been documented to be piscivorous, feeding primarily on salmonids; offshores, which are also piscivorous but feed primarily on sharks and other fish species; and transients, which feed primarily on marine mammals. Based on the occurrence of cephalopods in the stomach contents of two confirmed transient ecotype killer whales from the west coast of the United States, and two others that are likely closely related to the transient ecotype from across the North Pacific Ocean, we suggest that cephalopods may represent an underappreciated component of the diet of transient killer whales or closely related ecotypes throughout the North Pacific Ocean. Only cephalopods that are known to occur at relatively deep depths were present in the stomach of a killer whale from Hawai'i. The stomach of a killer whale collected in the Sea of Okhotsk not only contained marine mammal and fish parts, but also squid known to only occur at deep depths. Of the two whales from the west coast of the United States that were genetically identified as transients, one contained only squid and the other contained squid and marine mammal parts. If squid were to comprise a substantial portion of the diet in these west coast United States transient killer whales, instead of primarily marine mammals as currently thought, this could account for a mismatch between expected and observed stable isotope values of transient killer whales previously sampled in the eastern North Pacific.