Some cetacean species - bottlenose dolphins, common dolphins, dusky dolphins, killer whales etc. - are famous ‘fish ball’ hunters.
They gather together, circle around a school of fish, squish the fish into a ball, and then take turns swimming into the bait ball and eating the fish.
A new study suggests that sperm whales (Physeter macrocephalus) can probably do the same. Thanks to special tags attached to the animals, researchers could study movement, time and depth recorded during dives of several individuals within the same group.
‘We're speculating that the animals are herding a ball of squid’ said Professor Bruce Mate who led the study, and added: ‘Some whales appeared to guard the bottom of this bait ball, preventing the prey from sinking to unreachable depths, while other animals in the group took advantage of the centre of the ball’.
The sperm whale food-ball theory is not yet proved but researchers are working to better understand what happens when these giants feed at 1,000 m depth.
Silvia Bonizzoni
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Photo: a fish ball, at http://www.sea-way.org/blog/Beneath14.JPG
For more information:
http://news.bbc.co.uk/2/hi/science/nature/8530116.stm
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