Our whale of the month feature is back from a summer holiday!
Species fact file
Common names: killer whale, orca
Icelandic name: háhyrningur
Scientific name: Orcinus orca
Family: Delphinidae (dolphins)
Max length: 9.8m (males), 7.9m (females)
September’s whale of the month is the killer whale, or orca. Killer whales are the largest member of the dolphin family and they are found in almost every ocean on the planet: from coastal shallows to the open sea, from the tropics to the poles. You can meet them at the 4th stop on our audio guide.
Male killer whales are larger than females and have a very tall dorsal fin – it can reach up to 2m tall! This, along with their size and their distinctive black and white colouring, makes this species relatively easy to identify at sea. Their markings are like fingerprints: the shape of the dorsal fin and the light-coloured saddle patch behind it as well as the many scars and notches that a whale picks up throughout its life are unique. This means scientists can identify any killer whale from a photograph of them and provides information on where they are at different times of year, what they are feeding on, and which other killer whales they are socialising with.
Killer whales are top marine predators and as a species have a wide and varied diet, feeding on small fish, sharks, seabirds, seals, other dolphins and even some of the largest species of whales! However, in some places, killer whales can be very picky eaters. For example, the ‘resident’ killer whales of Washington state and British Columbia hunt for the same few species of salmon year-round, even when other kinds of fish are more abundant.
For many years, scientists thought that Icelandic killer whales had a similarly strict diet and only ate herring. Recent research has shown that some killer whales follow the Icelandic herring between their summer and winter grounds, and strongly suggests that they do prefer herring over other fish. But scientists found that other Icelandic killer whales travel to the north of Scotland in summer where they have been seen feeding on seals, just like the local Scottish killer whales. It seems that these orcas make this journey every year before returning to Iceland to feed on shoals of herring during winter.
We have known for a long time that killer whales are found around Iceland, but there has only been dedicated research carried out on this population recently, which is why we are still finding out so much about them.
One of these recent discoveries is the interesting and unusual interaction between killer whales and long-finned pilot whales in the herring spawning grounds of Vestmannaeyjar, a group of islands off the south coast of Iceland. Researchers have seen large groups of pilot whales harassing killer whales, approaching at high speed and driving them out of the area. We still don’t know why pilot whales do this – it may be a response to killer whales as potential predators, or as competition for prey – and this interaction is the focus of research by the University of Iceland.
Another area of ongoing research is the structure of Icelandic killer whale society.
Like all dolphins, killer whales are a very social species. Most of what we know about killer whale social structure comes from the ‘resident’ and ‘transient’ populations of the Pacific Northwest, which have been closely studied for decades. While the ‘residents’ are salmon specialists, ‘transient’ killer whales will only eat marine mammals – and this difference is reflected in their social structures. Despite living in the same area, these two populations are socially isolated and do not interact. However, Icelandic killer whales don’t seem to do this, as they are not socially divided based on their diet: those which hunt seals in Scotland over summer interact and socialise with the year-round herring specialists during winter months in Iceland.
This flexible, seasonally-variable society is very different to the rigid social structure of killer whales in the Pacific Northwest, and that we found these differences so recently shows just how much we still have to learn about this iconic and beloved species.
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