There are a lot of visitors to the Antarctic Peninsula every austral summer. Most of them are watching wildlife and taking hundreds of pictures. Popular science projects like Happy Whale provide a lot of digital photo material for marine mammal researchers all over the world. So one could assume whale populations and their characteristics especially in the frequently visited Antarctic Peninsula are well established. However, nature can still surprise us.
American marine mammal scientists have been looking closely at different groups of Killer whales in the South Polar Ocean during the past decade. We now know about four different ecotypes of Killer whales in Antarctic waters. The largest Killer whales belong to type A. They mainly hunt Minke whales in the open sea. Type B Killer whales live close to the coast or the pack ice of the Antarctic Peninsula and type C animals are feeding in the Ross Sea region. The so far youngest and least known ecotype D roams in sub-antarctic waters, known beyond others to feed on fish of long lines.
Type B Killer whale, Antarctic Peninsula.
Researchers have been observed differences in body size within type B Killer whales whereas the body colouration, such as the big eye patch and the dorsal cape, does not show significant differences. But apparently, there are differences in group size, feeding behaviour and preferred habitat.
A complex habitat with abundant food resources favour the specialisation of predators. Animals might partition resources and habitats amongst themselves. This is called “niche differentiation” in ecology. Where some species (or sub-species) have similar food and habitat requirements, they are usually separated geographically, e.g. Killer whale type B and type C. Is there enough space and resources available to permit coexistence within one area, niches can be differentiated locally by specialisation. Like that, different ecotypes can develop and even new species can evolve over time.
In future we might look at type B Killer whales as two different ecotypes. The larger are hunting seals in the pack ice or close to the coast, whereas the smaller feed on brush-tailed penguins (Gentoo, Adelie, Chinstrap penguin) and fish. Like that both groups belong to a different trophic level in the food web: the larger are feeding on predators of krill feeders, the smaller feed on the krill feeders themselves.
There seem to be small genetic differences already. Individuals of type B can still mate with each other considering their biology, but members of the different size groups obviously rarely do so. Scientists suppose that the genetic differentiation might have started with the end of the last glaciation period, when a lot of new space became available due to the retreat of the ice.