A scientist who has spent the last few years researching killer whales in Shetland led a study which has revealed there are two types of the mammal living in UK waters.
The two types vary in size, colour and feeding habits, with type one, the smaller of the two at six and a half metres for an adult male, the one most likely to be found in Shetland waters. A type two adult male will grow to eight and a half metres.
Dr Andy Foote, from the University of Aberdeen, will be familiar to many readers and wildlife enthusiasts having been in the isles during the past three summers.
In the study, for which samples were taken from throughout the North Atlantic, he looked at the feeding habits of killer whales as well as the remains of the mammals’ teeth.
While it is known there are variations of killer whale which have evolved through ecological differentiations in the Antarctic and Pacific, this is the first time studies of this type have been done in the North Atlantic, where it was previously thought there was just one type of the mammal.
The research, which has taken around three years, involved Dr Foote and his colleagues studying museum samples of teeth from the remains of killer whales over the past 200 years, and chemical traces from the diets of the mammals.
Dr Foote was assisted in his work by local expert Neil Anderson while in Shetland, where several samples were taken. Dr Foote said: “It’s a bit different to what we’ve done before and isn’t related to the other research work we’ve done in Shetland.”
During the studies, a difference in tooth wear was noticed. In the wild, killer whales that “suck up” herring and mackerel display this tooth wear. Knowing this, the researchers suspected a difference in diet and ecological preference between the two groups.
Dr Foote said: “We found that one form, which we call ‘type one’ had severely worn teeth in all adult specimens. The other form, ‘type two’, had virtually no tooth wear even in the largest adults.
“The two types also differed in length, with type two adult males being almost two metres larger than types one males.”
Using stable isotope analysis – the analysis of chemical traces from the mammals’ diet – the scientists found that type one is a generalist feeder, consuming fish and seals.
Type two, on the other hand, is a specialist feeder that scientists suspect exclusively feeds on marine mammals such as small dolphins and whales.
This specialisation for alternate ecological niches has also resulted in a difference in shape and appearance, with colour, pattern and number of teeth varying between the groups.
Dr Foote explained: “It’s similar to how Darwin’s finches have adapted to different ecological roles in the Galapagos, but on a larger scale.
“They seem to have occupied completely different ecological niches and have started to diverge morphologically. This divergence may eventually lead to the two types becoming different species.”
However Dr Foote said that at the moment, the research points to them being different “races” of the same species, as it is not yet known whether they are reproductively separate or whether the two types mate.
The findings could be important for the future of the animals and their conservation. Dr Foote said the groups should be monitored separately to allow for effective conservation work.
He said: “It’s exciting to think about two very different types of killer whale in the waters around Britain.
“Killer whales aren’t really a species that we think of as being a regular visitor to Britain, but in fact we have two forms of these killer whales in our waters.
“It’s useful for conservation as instead of looking at how many killer whales there are in any given area, we need to look at how many of each type.”