Over the last few decades, as wild orca research has expanded, researchers have described different forms or types of orcas.
Known as ecotypes, these distinct types of orcas differ in size, appearance, prey preferences, foraging techniques, dialects, behaviours, and social groups. Their ranges often overlap, but they are also genetically distinct – they don’t appear to interbreed, and rarely interact with other ecotypes.
Resident orcas are fish-specialists, named so because they tend to have small home ranges around areas of large fish populations. Residents are found on both sides of the North Pacific; the Northern and Southern communities almost exclusively eat salmon, while Residents in Alaska appear to be more generalist in their fish preference, eating multiple fish species including salmon, mackerel, halibut and cod. Research by the Far East Russia Orca Project (FEROP) has shown that fish-eating orcas off the coasts of Russia and Japan prefer salmon and mackerel. Resident orcas live in family groups within larger communities, divided by matrilines and pods, and offspring live with their mother for their entire lives. These communities are genetically and acoustically distinct from each other, and each has unique traits specific to their group, like the beach-rubbing behaviour of the Northern Residents.
Another North Pacific ecotype is Bigg’s, or transient, orcas. These are mammal-eating orcas, and like Residents, different communities of Bigg’s orcas specialize on different prey – from harbour seals to minke whales to gray whale calves. They live in small groups and travel frequently over large home ranges, from Southern California up to the Arctic Circle. Also very family-oriented, Bigg’s orcas live in smaller groups but form close associations with their relatives, and some offspring stay with their mother for life. Transient orcas have been recorded by FEROP in the Western North Pacific, and populations on both sides of the Pacific carry high loads of contaminants. As top predators, these mammal-eating orcas accumulate pollutants that are transferred through the food web and end up stored in the blubber of these whales.
The third ecotype found in the North Pacific, little is known about the elusive Offshore orcas, as they live far from land – mainly over the outer continental shelf - and are rarely encountered. Their large range stretches from Southern California to the Bering Sea, and their social structure and prey preferences are still unknown. They are usually seen in large groups with more than 50 individuals, and have been seen preying on both fish and sharks. The teeth of Offshore orcas are often worn down, indicating that they’re eating things with rough skin (like sharks). They are the smallest of the three North Pacific ecotypes, and are more closely related to Residents than to Bigg’s orcas, though all three ecotypes are genetically distinct.
North Atlantic Type 1
These small orcas live in closely related pods and appear to be generalist eaters. They are known to feed on large runs of herring and mackerel around Norway, Iceland, and Scotland; and some have been seen feeding on seals as well. Like other orca ecotypes, different communities have different prey preferences and have different home ranges. Type 1 orcas off Norway have been observed using a carousel feeding technique, herding herring into dense balls, then slapping with their tails to stun the fish. Research on Type 1 orcas is ongoing, and photo-identification studies are gradually revealing the size and population structure of these orcas; they may be more divided into separate populations than previously thought.
North Atlantic Type 2
Type 2 orcas prey primarily on other whales and dolphins, particularly minke whales. These rarely-seen orcas are large, with distinctive back-sloping eye patches, and like other mammal-eating orcas, they are especially threatened by high contaminant loads. Similar to the different ecotypes in the Pacific, the prey specializations of Type 1 and Type 2 orcas are reflected in their teeth – Type 1 orcas have very worn teeth from feeding on fish, while Type 2s have larger and sharper teeth for hunting other mammals.
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