Pilot whales are the cheetahs of the oceans, focusing their hunting effort on short, intense chases after a few rich food items. They are the first deep-diving whales known to follow such a strategy.
Whales such as sperm whales and beaked whales, which feed during deep dives that take them hundreds of metres below the surface, have to find and capture prey while holding their breath.
Until now, biologists had assumed that all deep-diving whales would cruise slowly and graze on slow-moving prey items while underwater, since this minimises their energy expenditure.
Using this strategy, most deep-diving whales can spend nearly an hour at a time underwater. Pilot whales, however, are the exception – their dives last no more than 15 to 20 minutes.
To find out why, Peter Tyack of Woods Hole Oceanographic Institution in Massachusetts, US, and his colleagues suction-cupped data recorders to 23 short-finned pilot whales off Tenerife in the Canary Islands. During the few hours the recorders stuck to the whales, they logged sound and movement for a total of 59 dives to more than 500 metres depth.
Nutritious reward
Near the bottom of most, but not all, of these dives, the recordings showed that whales made a sudden sprint of 30 seconds or less, accompanied by a furious burst of echolocation clicks, which usually signals a nearby prey item.
The researchers calculated that this short sprint consumes, on average, about 22% of the entire oxygen use for the dive, during just 3% of its duration – a huge cost for a breath-holding animal to pay.
Such a cost would need a large potential payoff. "They look like they are going after big, nutritionally rich prey," says Tyack.
The researchers are not sure exactly what the whales were eating on the dives they measured, but other studies have found large, muscular – and hence, especially nutritious – squid in the stomachs of pilot whales.
Journal reference: Journal of Animal Ecology (DOI: 10.1111/j.1365-2656.2008.01393.x)
Pilot whales are the sprinters of the deep - life - 14 May 2008 - New Scientist
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