When Killer Whales were observed by Spanish sailors, who frequently saw them attacking another whale, they described these great creatures as “whale killers”. Orcinus orca subsequently became known as the killer whale.
The killer whale is an an odontocete, a sharp toothed cetacean, and is the largest of the oceanic dolphins, the delphinidae. The killer whale is one of the fastest underwater mammals, and one of the most widely distributed in all the oceans of the world.
Orcas live socially, in matriarchal pods, consisting of up to fifty males, females and calves. Resident killer whales feed mainly on fish, but the transients eat only other mammals, hunting in pods for dolphins, seals, sea lions, and whales. Transients have been observed attacking fully grown blue whales, the largest existing animals in the world today. Transient killer whales are often covered in scars, and frequently have bent dorsal fins, from their hunting activities.
Richard Ternullo and Nancy Black studied predation behavior of transient killer whales in Monterey Bay, California, and in 2002 they presented the results of this research at the Fourth International Orca Symposium, held in France.
In Monterey Bay, the research whalewatchers had observed killer whales pursuing and harassing blue whales. Several humpbacks, and one beached minke whale, also showed evidence of Killer whale attack. Gray whales were more regularly seen under attack. A significant number of gray whale calves provided food for the killer whales during the migration of female gray whales and their calves.
Gray whale calves are much larger than the killer whales, but adult orca males are capable of using sufficient force to decapitate a gray whale calf. Adult female orcas hunt co-operatively as a group, with one large female separating the gray whale mother from her calf, and the smaller females harassing the gray calf and holding it underwater until it has drowned. The pod will then spend up to seven hours feeding off the calf. Male killer whales will join in the when feeding commences. All the blubber is stripped off the gray whale for consumption, and orcas also consume the huge tongue of the gray whale calf.
Between 1994 and 2002, researchers conducted a survey of gray whale calves in Monterey Bay. They recorded many more attacks by killer whales in years when they counted a high number of gray whale calves in the bay, and far fewer when low numbers of grey whale calves appeared. In 1999, only three attacks were recorded.
The whaling industry caused the gray whale to become an endangered species, but since it became protected by law, the gray has almost returned back to its original numbers, and is once again competing for food with the other whale species. At the top of the marine food chain, the killer whale seems to play an important part in maintaining the ecological balance.