Published online 14 January 2000 | Nature | doi:10.1038/news000120-2

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A stunning performance

Killer whales slap their prey into submission before eating them, says Eleanor Lawrence.

Underwater movies of killer whales (Orcinus orca) feeding on shoals of herring (Clupea harengus) off the coast of Norway reveal how these whales use their powerful tails to stun the fish before picking their prey off individually, Paolo Domenici from the International Marine Centre at Torregrande, Italy, and colleagues report.

Image © NOAAImage © NOAA

This way of killing and catching food is much more efficient for such a large mammal than chasing each fish individually, they explain in the Journal of Experimental Biology1. They estimate that a whale can stun around 16 fish at a time with one blow of its tail.

Killer whales are shaped much like torpedoes, measuring around six metres long on average (although they can reach up to nine metres). They weigh anything between one and five tonnes. The last quarter of a whale's body forms a muscular tail. This ends in a broad flat triangular fluke, which can pack a powerful punch when rapidly slapped down by muscular contractions in the tail. Domenici and colleagues' video reveals that the fish are stunned by actual physical impact with the underside of the fluke -- a successful 'hit', as judged by the appearance of disoriented herring, was always accompanied by a loud bang.

The researchers filmed the killer whales hunting in 'pods' of 10 to 20 animals. They swim round and under the shoal of fish, herding it into a tight ball near the sea surface. Once they get the fish cornered, the whales make periodic swift lunges into the shoal. These seem to be concerned with directing the movement of the fish, rather than actually catching prey, and are often followed by a stunning tail slap. Whales swimming around the perimeter of the shoal join in the fun, delivering yet more blows.

Tail slaps were always made while the whale was completely submerged, and the effect was pretty much like swatting flies. The researchers estimate that a whale could theoretically stun between 10 and 47 fish at one blow, although the actual number is likely to be about 16. The stunned fish are then eaten one by one.

By analysing the position of the tail-fluke in successive video frames of a single tail-slap, Domenici and his colleagues found that the fluke started off almost vertical to the water surface. It was then brought slightly forward and then sharply down, so that the leading edge described an S-shaped curve. Each tail flick lasted only a second, and rarely missed.

So given the relatively poor acceleration and manoeuvrability of such a large animal as a killer whale, compared to a small fish like the herring, the whale's use of its mobile tail fluke as a herring-swat is a highly efficient way of gathering food. 

  • References

    1. Domenici,P., Batty, R.S., Similä, T. and Ogam, E. Killer whales (Orcinus orca) feeding on schooling herring (Clupea harengus) using underwater tail-slaps: kinematic analyses of field observations. The Journal of Experimental Biology 203, 283 - 294 2000. | PubMed |