Killer Whale Diet
The Complex Predator
Almost everything about the killer whale is more complex than it first appears. Around the world, killer whales attack and feed on prey ranging in size from herring to blue whales. They’re known to take mackerel, salmon, tuna, squid, sea turtles, sharks, seals, sea lions, porpoises, dolphins, grey whales, minke whales, and many other species. Knowing this, it would seem that no swimming marine animal more than about 20 cm long is safe from these awesome predators. Globally speaking that may be true---but locally, nothing could be further from the truth. Individual killer whales tend to have very specialized diets and in fact DON’T feed on all prey that are available to them. Furthermore, their food preferences are learned from family members and shared by other members of their population. As you explore this site, you’ll learn that some killer whale populations in the NE Pacific Ocean only eat fish, others only eat marine mammals, and some appear to specialize on sharks. To make things really confusing, these populations overlap—although it appears that they don’t socialize or mate with each other.
Top photo: John Durban Killer whales hunting a gray whale in the north Pacific; king penguins at the Crozet Archipelago, and herring in Norway.
Middle and bottom photo: Lance Barrett-Lennard
Is Picky Eating Common in the Marine World?
Foraging and feeding specialization has been described in a few other marine animals, notably sea otters, bottlenose dolphins, and a few sea birds, but only killer whales are known to have entire populations that single-mindedly focus on some types of prey while ignoring others. In fact, killer whale food preferences are so strong that the safest place in the ocean may be next to killer whales that specialize on other prey species. Killer whales from different populations maintain their distance from each other, which means that a dolphin associating with fish-eating killer whales is safe from mammal-eating killer whales—and it may be able to steal a few scraps of fish to boot.
How Do Killer Whales Come by Their Food Preferences?
We probably shouldn’t be surprised that individual killer whales have strong opinions about what they want—and don’t want—to eat. Every human culture has foods that it esteems. Every culture also finds some perfectly edible foods repugnant—locusts and fresh cow’s blood would be examples for most Westerners. We learn our tastes culturally—from family, friends, and others in our society. Killer whales are similar to humans in that they pass on information, including traditions, customs, and food preferences by a process of social learning. Both species have low reproductive rates and take many years to mature sexually—offspring are few and precious. Risk is minimized if learning is by example, not by trial and error. The most reliable method of choosing a safe diet is to learn one’s food preferences from one’s parents.
Why Do Killer Whale Populations have Different Food Preferences?
It’s all about competition—probably. The British scholar Malthus pointed out 200 years ago that all populations have the capacity to grow until they run out of resources. Competition for resources is a fact of life, and the most successful individuals are either the best competitors...or they’ve figured out ways to escape or lessen competition. Killer whale populations have different histories and are likely to have somewhat different dietary preferences just by chance. If two killer whale populations overlap, they can lessen food competition by increasing their differences and focusing on entirely different types of food. Once this dietary separation is established, social tradition likely makes it difficult and slow to reverse. So, co-existing fish-eating and mammal-eating killer whales probably don’t know that they have pushed each other into different ecological niches, but they likely do know that there’s no dietary overlap and no reason for conflict.
Evolution and Diet
Did the evolutionary ancestors of killer whales eat fish, marine mammals, or both? At a simple level, the morphology (form and structure) of killer whales does not appear to reflect their well-known ability to tackle dangerous prey. They have no armour and their skin is soft and sensitive. Their conical teeth are adapted for puncturing and holding, rather than slicing flesh or crushing bone, and they aren’t as big as one would expect in a killer of whales. Their bodies are smaller and their swimming speeds slower than some of their mammal prey. Their lower jaw is not particularly robust, and the section behind the back teeth is positively fragile. Their dives rarely exceed 350 m and 15 minutes--less in both respects than many other marine mammals. In general, their appearance and physical abilities suggest that their lineage fed on fish or other relatively small prey throughout most of its evolutionary history.
The Killer’s Secret
If the bodies of killer whales are best suited for killing fish, why are they so successful at taking marine mammals as well? First, they use their secret weapon—their large brain—to develop specialized hunting strategies. Second, they hunt in highly-coordinated groups that are terribly difficult to evade or resist. Some people refer to killer whales as the Tyrannosaurus of the sea. In reality, they are much more like the Homo sapiens of the sea—they look meek, but achieve terrifying power through intelligence and teamwork.
Photo: Lance Barrett-Lennard
Killer whales learn their food prefence from their mothers.
Photo: Lance Barrett-Lennard
The underside of a killer whale skull.
Photo: Lance Barrett-Lennard
A group of transient killer whales hunting along the rocky shore of Unimak Island, Alaska