Our recent acoustic study suggests that killer whales in Iceland and Norway may not have been one completely mixed population as previously thought. We found that, while the basic properties of Icelandic and Norwegian killer whale calls are similar, they do not share any call types.
Killer whales in Iceland and Norway are very similar in their genetics, morphology and behaviour. They mostly feed on herring and use similar techniques to capture this prey. Before the 1960s, the Norwegian herring stock was distributed all across between Norway the East shores of Iceland. Catches from whalers and sighting information indicated that killer whales were distributed uniformly in this region, suggesting one population spread out between Iceland and Norway. However, more recent studies using photo-identification could not match any individuals between Iceland and Norway. Therefore, it was thought that the collapse of the herring stocks in the 1960s lead to a split in the population, with the whales retreating closer to the coastal areas of Iceland and Norway, where there was still herring to be found.
Recording killer whales in Iceland
We compared acoustic recordings of killer whales collected in Iceland, Norway and Shetland between 2005 and 2016 to see if the whales in these locations share any calls. The idea was that if the whales that we see in these locations were all a single, mixed population in such a recent past we might expect to see some calls that are the same. In other well-studied killer whale populations, such as the North Pacific residents for example, call repertoires reflect relatedness, with closely related whales sharing more calls than distantly related ones. From these studies we also know that call repertoires in wild killer whales only change very slowly.
Processing calls in the lab
The first step in comparing call repertoires is to collate catalogues of the calls recorded in different locations. For Iceland, only a small catalogue from the 1980s existed. From our collection of over 700 hours of recordings from Iceland, Norway and Shetland, we extracted over 12.000 high quality calls. We used these calls to create a call catalogue for Iceland and updated existing catalogues from Norway.
Once the call catalogues were established, we compared the calls from each location and found that while they share similar basic properties of duration and frequency, killer whales from Iceland and Shetland share a few call types but whales from Norway do not appear to share any call types with the others.
Visual representation and corresponding sounds from a recording of killer whale calls from Iceland.
Visual representation and corresponding sounds from a recording of killer whale calls from Norway.
These findings are similar to what we know from the most recent photo-identification studies. There have not been any matches of individuals between Iceland and Norway or Shetland and Norway. However, there are several individuals that regularly migrate between Iceland and Shetland.
This analysis was the first step in answering the question of how call repertoires vary across the North Atlantic and within different groups or regions. We are already working on new projects trying to learn more about the vocal behaviour of killer whales in Iceland. For example, we are looking at variation in the repertoire between locations in Iceland as well as between different groups of individuals. Understanting how killer whales in different locations are (and used to be) connected is important to assess the status of this top predator in the North Atlantic.
Like most of the work we do, this study was a great team effort with wonderful support from our international collaborators: Selbmann A, Deecke VD, Fedutin ID, Filatova OA, Miller PJO, Svavarsson J and Samarra, FIP (2020) A comparison of Northeast Atlantic killer whale (Orcinus orca) stereotyped call repertoires. Marine Mammal Science, doi: 10.1111/mms.12750 Available here or contact us for a pdf
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