How well do you know your orcas?
Orcas are both iconic and dangerous, maintaining a reputation as the top predator in the ocean. It was once thought that there was only one type of orca, but thanks to a combination of evolution and wild orca research, we now know that this is not the case. There are in fact several different types (also termed ecotypes or subspecies) of orca, which can be differentiated on the basis of their diet, hunting techniques, markings and acoustic behaviours. These individual groups of orcas do not interbreed, despite having a degree of range overlap. So far, we are aware of the following ecotypes of orca, which can be split into groupings depending on their geographical range:
- Resident Orcas –Found in the north pacific, resident orcas are fish specialists, consuming a variety of fish species including salmon and mackerel. These orcas can be subdivided further based on location and fish preferences- Resident orcas in Alaska for example are more generalist in their approach to fish, compared to northern and southern communities who consume mostly salmon.
- Biggs Orcas- Like resident orcas, Biggs orcas also reside in the north pacific and can be subdivided into communities which have distinct dietary preferences. All of these orcas are mammal eating, but some communities feed on harbour seals and others on minke or grey whales. These whales have large home ranges and travel frequently between southern California and the Arctic Circle. These orcas are known to carry high levels of toxins which have worked their way up through the food chain and end up being stored in the blubber of orcas.
- Offshore– the final type of orca found in the north pacific (at least that we know of) are offshore orcas. Less is known about these orcas as they reside far away from land. What is known is that offshore orcas have been seen in large groups of around 50 individuals preying on fish and sharks. Offshore orcas are small than Biggs and Resident orcas, and despite all residing in the north Atlantic, these three ecotypes are genetically distinct.
- North Atlantic type 1– These orcas are smaller than other types, and tend to be generalist feeders. They are known to feed on fish and seals (again, this type or orca can be subdivided with different communities exhibiting different feeding preferences) and have been observed employing the ‘carousel’ method of hunting. Here, orcas herd fish into tight balls before slapping them with their flukes to stun them.
- North Atlantic type 2– Type 2 orcas are known to feed on whales and dolphins, especially minke whales. They are larger than type 1 orcas and possess sharper teeth. Like other mammal eating orcas, type 2 are threatened by high toxin levels.
- Type A- These orcas are large and inhabit the open ocean. They migrate in and out of Antarctic waters and mainly feed on minke whales.
- Type B– these orcas can be further split into two types- large and small. Large type B orcas feed on seals on loose ice sheets in the Antarctic. These orcas are also known as Pack ice orcas due to their famous wave washing hunting technique. Small Type B (also known as Gerlache orcas, after the Gerlache Strait of the Antarctic Peninsula where they are most often found) are thought to feed on penguins, though little is known about their dietary preferences. Both large and small type B orcas may appear brown/yellow because of the presence of diatoms (a group of algae) on their skin.
- Type C- The smallest of all ecotypes, type C, or Ross sea orcas, are typically seen in East Antarctica and are known to feed on Antarctic tooth fish.
- Type D– These orcas are rare but are known to have a distinctive look compared to the other orca ecotypes- they have shorter dorsal fins, rounder heads and small eye patches. Like Ross Sea orcas they are known to consume tooth fish. It is not known if their diet includes any other animals.
Further ecotypes and implications for conservation
It is likely that there are other ecotypes of orca. Communities in the strait of Gibraltar and the British Isles for example are likely to be distinct from other orca types, though not enough research has been done to confirm this. There is concern that small populations such as the resident group around New Zealand may be lost in the future as they do not appear to interbreed with other communities and we lack the knowledge to properly assess their uniqueness, alongside the threats they are facing.
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