Most of you have probably heard about resident and transient killer whales. They are the most studied killer whales in the world, and they can be found off the west coast of North America. But did you know there are killer whales in the Antarctic as well? Some scientists estimated they are around 25 000 killer whales around Antarctica, but detailed estimates are difficult to obtain in the Southern Ocean. Future research might tell us exactly how many killer whales live in Antarctica.
What we do know, however, is that not all killer whales in the Southern Ocean share the same habits. Scientists have described four major ecotypes: A, B (B1 and B2), C, and D. In this post; we will focus on type B killer whales and provide an overview of their dietary habits. We’ve also partnered with Lauryn Fly, a science illustrator who loves marine mammals, to create a representation of the type, as well as some of its hunting techniques.
What is an ecotype?
On top of being extremely charismatic top predators, killer whales are also one of the most diverse species of marine mammals. Killer whales are a cosmopolitan species: they live pretty much everywhere. And although their distribution spans from polar waters to tropical seas, killer whales are separated into different “ecotypes” that tend to have adapted to a specific environment. An ecotype is roughly defined as a group of individuals within a species that specialize in specific prey and have distinct patterns of movement, behavior, and social adaptations that are linked to this dietary specialization. Because these killer whale ecotypes share common adaptations, they tend to be genetically different. As a result, some scientists suggested they should be considered different species.
In the Southern Ocean, scientists have described four main ecotypes. Type A is a large killer whale that typically follows minke whales, its favorite prey, around Antarctica. The second type, Type B, is smaller and separated into two sub-types (more below). Type C lives almost exclusively around the Ross Sea and feeds on fish like Antarctic toothfish. Finally, type D is the most mysterious Antarctic ecotype; it has a different morphology, and some scientists believe type D killer whales are an entirely different species of killer whales. We might dedicate future posts to the different types, so make sure to let us know if you would like to find out more about them.
Type B is a complex ecotype
Killer whales of this type have very large eye patches and typically show a beautiful pattern of grey on their back called a “dorsal cape.” They can appear yellowish at times because of the diatoms (cold water algae) that grow on their skin. Type B killer whales are considered smaller than their big type A conspecifics. That being said, adult males from the type B ecotype still range between 6 and 8m (20-26 ft) meters. However, things get a bit more complex because there are two sub-types B! Type B1 killer whales are slightly larger than type B2.
Size is not the only thing differentiating the two types. B1 killer whales typically feed on seals, travel in small groups, and stick to the ice pack, where they can hunt easily. B2 killer whales tend to travel in larger groups and feed on a larger range of prey: penguins, fish, and occasionally Weddell seals. Despite their differences in morphology, feeding strategy, and group sizes, both subtypes coexist in the same environment.
Yet, B1 killer whales are the rarer type and might face critical threats due to climate change. A recent study focusing on the Western Antarctic Peninsula reported that the population size of type B1 (~100 individuals) is smaller than type B2 in the area (~740 individuals). The study’s authors also estimated that the population of B1 killer whales is declining annually (by about 5%), which they believe could be explained by climate change and the loss of sea ice. Let’s focus on type B1’s hunting techniques to understand why sea ice is so important to them.
A unique hunting technique
Type B1 killer whales can hunt seals in a spectacular way. To do so, they spy hop (raise their heads above the water) to locate seals resting on sheets of ice. Once they spot a prey (usually a Weddell seal), they coordinate their attack and start charging toward the ice floe at full speed. Once close to the ice, they send a large wave that washes the seal off the ice and into the water, where the rest of the group is waiting. Seals have very little chance of escape once they are in the water. A study focusing on this hunting technique reported that out of 16 seals targeted by the whales, 12 were successfully eaten.
These spectacular hunting events are one example of the impressive range of ecological adaptations of killer whales. Killer whales are incredibly smart and capable of developing intricate strategies to hunt their favorite prey. Yet, because of climate change and the loss of sea ice, B1 killer whales may have to relocate or adapt their hunting strategies to survive in this changing environment.
Did you enjoy reading about type B killer whales? Make sure you let us know what type you would like us to focus on next time! In the meantime, please make sure to check out Lauryn’s incredible illustrations!
Sources and further reading
- de Bruyn, PJ Nico, Cheryl A. Tosh, and Aleks Terauds. “Killer whale ecotypes: is there a global model?.” Biological Reviews 88.1 (2013): 62-80.
- Forney, Karin A., PAUL R. Wade, and J. A. Estes. “Worldwide distribution and abundance of killer whales.” Whales, whaling and ocean ecosystems 145 (2006): 162.
- Pitman, R. L., and P. Ensor. “Three different forms of killer whales in Antarctic waters.” Journal of Cetacean Research and Management 5.2 (2003): 131-139.
- Fearnbach, Holly, et al. “A decade of photo‐identification reveals contrasting abundance and trends of Type B killer whales in the coastal waters of the Antarctic Peninsula.” Marine Mammal Science 38.1 (2022): 58-72.
- Pitman, Robert L., and John W. Durban. “Cooperative hunting behavior, prey selectivity and prey handling by pack ice killer whales (Orcinus orca), type B, in Antarctic Peninsula waters.” Marine Mammal Science 28.1 (2012): 16-36.