Orca fins washing up in the North Pacific are scratched with characteristic tooth marks that suggest killer whales are occasionally cannibals. Scientists say this may explain why some orcas live in large family groups.
Orcas (Orcinus orca) come in several distinct types, sometimes considered different subspecies. In the North Pacific Ocean, two of these types inhabit roughly the same areas: Resident orcas (Orcinus orca ater) live in large family groups and eat fish, and Bigg's orcas (Orcinus orca rectipinnus), which are more common and transient, live in smaller groups and hunt other mammals, such as whales, dolphins and seals.
