Killer whales are found in every ocean of the world. They are the most widespread mammals other than humans. While they are all technically the same species (stay tuned—there has been talk about reviewing species and subspecies distinctions), they are all separate breeding populations, each with their own language, social structure, food preference and hunting behaviours—essentially their own culture. This is passed on from the older generations to the younger ones in much the same way as it is in humans. So while technically, the different ecotypes can interbreed and produce fertile offspring (thanks, SeaWorld, for proving that one [cough sarcastically]), in the wild, they don’t. Showing that they are much smarter than humans, they seem to have some sort of silent agreement that even though they may live in the same waters, since they’re not competing for the same resources, they generally just avoid each other. No fighting! No war! No genocide! Everyone wins.
It is likely that the different ecotypes evolved in different places (perhaps separated by glaciers, etc.), learning to feed on whatever prey was abundant in their area. By the time they found themselves in the proximity of other killer whales, they had been reproductively isolated for so long that the thought of interbreeding probably didn’t even occur to them. In BC, Bigg’s (aka transient) killer whales are thought to have diverged from other killer whale populations over 700,000 years ago. This is known as cultural divergence.In the North Pacific, there are three distinct ecotypes: resident (fish-eaters who prefer Chinook salmon) and Bigg’s killer whales (connoisseurs of marine mammals) occur in the coastal waters of the North Pacific, while offshore killer whales (with a palate for sharks) are mostly found—you guessed it—offshore. The same sorts of distinctions occur in the North Atlantic: type 1 eastern north Atlantic killer whales prefer herring or mackerel, which are plentiful there, and type 2 prefer marine mammals, mostly other whales and dolphins.
In the southern hemisphere around Antarctica, there are at least 5 different ecotypes of killer whales. (We’ll forgive researchers for not being certain about this, as it is a rather harsh and inhospitable climate). Antarctic type A killer whales tend to stay away from the ice and feed mostly on minke whales. Type B have recently been split into two groups: pack ice killer whales feed on seals around the outer pack ice, and smaller Gerlache killer whales (named after the Gerlache Strait on the Antarctic Peninsula in which they are often found) feed mainly on penguins. Type C or Ross Sea killer whales are piscivores, feeding mainly on fish and following channels or openings in the pack ice. Types B and C have a distinctive yellowish colour from diatoms on their skin, as well as a prominent dorsal cape. Type C is the smallest known killer whale ecotype. Last but not least is the Type D or subantarctic killer whale, with its tiny eyepatch and distinct shape, which been seen only a few times (including a few years ago off the coast of Chile).
There you have it! It is also important to note that while there are three ecotypes of killer whales in BC, they are further separated into distinct breeding populations. The endangered southern resident killer whale population, the best known in the world (thank you Center for Whale Research for 40 years of study, and Dr. Mike Bigg for pioneering the photo-identification techniques we still use today), contains only 83 animals. The northern residents, also fish-eaters, are a much larger population, numbering almost 300 animals. Bigg’s killer whales are also separated into several distinct breeding populations. So you see, conservation is not just about whether or not two animals can breed together to produce offspring; it is about ensuring the continuity of the culture, the language, the way of life… much as it is in humans. If the SRKW population continues to dwindle, would they eventually interbreed with the Northern Residents? Observations of the AT1 population of Bigg’s killer whales in Alaska, who were severely affected by the Exxon Valdez oil spill, indicates that they won’t. But let’s hope we never have to find out.
Special thanks to Uko Gorter for use of his illustrations. A picture says a thousand words!