Killer whales are probably several different species

Three different Antarctic killer whales: Top - Type A; Middle - Type B; Bottom - Type C (as designated by Pitman and Ensor, J. Cetacean Research and Management.

April 2010. Scientists report finding strong genetic evidence supporting the theory that there are several species of killer whales (Orcinus orca, also known as orca) in the world's oceans.

Very different behaviour patterns
Scientists have suspected for some time that there was more than one species of killer whales because of differences in behaviour, feeding preferences and subtle physical features. But until now DNA analysis has been inconclusive because of the inability to map the entire genetic picture, or genome, of the whales' mitochondria.

Mitochondria
"The genetic makeup of mitochondria in killer whales, like other cetaceans, changes very little over time, which makes it difficult to detect any differentiation in recently evolved species without looking at the entire genome," said Phillip Morin, lead author and geneticist at the Southwest Fisheries Science Centre in California. "But by using a relatively new method called, 'highly parallel sequencing' to map the entire genome of the cell's mitochondria from a worldwide sample of killer whales, we were able to see clear differences among the species."

The following killer whales are recommended for separate species status: 

Type-B "pack ice killer whale" from the Antarctic. Note the large eye-patch and two-tone gray color pattern. This type specializes in hunting seals, which are often on the ice and need to be knocked off the ice by the whales before they can be caught.  Photo Credit: Bob Pitman, NOAA Southwest Fisheries Science Center

Type-C "Ross Sea killer whale" from the Antarctic. Note the narrow angled eye patch. These are the smallest of the 3 Antarctic types and they eat fish that are found primarily under the ice pack, so they follow leads deep into the ice as it breaks up in the summer months. Photo Credit: Bob Pitman, NOAA Southwest Fisheries Science Center

Type-A killer whale from the Antarctic. Note the striking black and white colour pattern. This type is found in open water areas and feeds primarily on other cetaceans (whales and dolphins).   Photo Credit: John Durban, NOAA Southwest Fisheries Science Center

NE Pacific Transient killer whale in Alaska. Note the typical black and white colour pattern and eye-patch, similar to Antarctic Type A killer whales (left), but genetically distinct. The Transients are known to feed on all types of marine mammals, including other whales, dolphins, and seals and sea lions.  Photo Credit: Dave Ellifrit, NOAA Alaska Fisheries Science Center

139 killer whale samples analyzed - Several species identified
In all, tissue samples from 139 killer whales were analyzed. Samples came from killer whales found in the North Pacific, the North Atlantic and oceans surrounding Antarctica. As a result of the study, two types of killer whales in the Antarctic that eat fish and seals, respectively, are suggested as separate species, along with mammal-eating "transient" killer whales in the North Pacific. Several other types of killer whales may also be separate species or subspecies, but additional analysis is required.

New technology
Highly parallel sequencing of DNA is far faster and less costly than historical methods of analysis. For instance, the examination of mitochondrial DNA genome in one sample could have taken as long as several months. But with the use of high throughput sequencing, researchers can complete the same analysis for 50 or more samples in just a few weeks, and technology to sequence larger parts of the genome and more individuals continues to improve rapidly.

Determining how many species of killer whales there are is critically important for resource managers to establish conservation priorities and to better understand the ecological role of this large and widespread predator in the world's oceans.

The report was published in the journal Genome Research