Residents have shown no such propensity for violence against mammals, however. They feed exclusively on fish, ignoring the seals and sea lions that are often nearby. They have also developed a social structure that may be unique among mammals. A resident pod is a tightly closed unit, dominated by a matriarch. Nobody leaves the group unless they die.
Nobody gets in unless they are born into it.
That, of course, poses an inbreeding problem. Ford said it is a mystery as to how the resident pods deal with that, but clearly the females are somehow finding mates from outside the group. A top priority for researchers like Ford is finding out where the Strait of Georgia's resident whales go when they vanish in the fall. We just don't know. The vastness of the coastline and the notoriously bad weather in winter has limited research efforts.