It has been known for a long time that whales and dolphins are incredibly intelligent animals but it’s not often we see that intelligence so impressively displayed as when orcas (often called killer whales) hunt. Orcas can actually be divided into several different ‘types’ which are found in different areas of the world and often specialise in hunting different prey. Some, such as those around Norway and Greenland, are particularly adept at hunting herring and follow the fishes migration path. Others, such as those in the north-east Pacific are skilled salmon hunters, and some have even learnt to strip tuna fish from fisherman’s lines. There is one group however that outclasses them all, the orcas of the Antarctic peninsula have become specialised at taking seals from floating ice and the way they do it is simply breathtaking. Ingrid Visser and her colleagues were lucky enough to observe the attack in 2006 and described it like this
…one killer whale remained in position with its rostrum against the ice floe while four killer whales moved away from the ice floe with the seal on it. These four killer whales reappeared simultaneously, approximately 20 seconds later in line-abreast with all submerged just under the surface. All four were coordinated-swimming, with their left sides orientated towards the surface. A trail of bubbles emanated from each of the animals blowholes as they accelerated and passed directly under the ice floe, two on each side of the stationary killer whale. This generated a large wave, which tipped the ice floe initially towards the wave, then as the wave poured over and crested under the ice, it pivoted and tilted the ice in the other direction where the attacking whales were now waiting. The breaking wave washed the seal into the water…
This same hunting technique, sometimes termed “wave-washing”, was later filmed by the BBC for the series Frozen Planet (highly recommended if you haven’t yet seen it).
As someone who has worked with seals a lot over the last few years I have mixed feelings about this. On the one hand the seal is clearly distressed and is tormented for a very long time before it is finally killed, but on the other I can’t fail to be impressed by the skill and intelligence of the orcas that is required to pull off an attack like this. For this hunting strategy to be succesful there must be forward planning, and a high level of communication and coordination between individual orcas. These characteristics are not often associated with animals.
What is really interesting is that in the case described by Visser and her colleagues the seal was caught after around 15 minutes but then released and allowed back onto the ice. It then had to endure a second wave-washing attack before being finally killed almost 15 minutes later. Why did the orcas not kill and eat the seal immediately? The answer is not known, it could simply be play behaviour or, more interestingly, it may be that the adults are training their young to hunt. We clearly have a lot more to learn from these amazing animals and I expect there will be many more discoveries in the future.
For a detailed description of this behaviour see:
Visser I.N., Smith T.G., Bullock I.D., Green G.D., Carlsson O.G.L. & Imberti S. (2008). Antarctic peninsula killer whales (Orcinus orca) hunt seals and a penguin on floating ice, Marine Mammal Science, 24 (1) 225-234. DOI: 10.1111/j.1748-7692.2007.00163.x