May 15, 2008

Study Shows Pilot Whales Sprinting After Large Prey

Under the sea, predatory pilot whales take part in high-speed chases as they track down their prey.

The cetaceans have been observed reaching such high speeds that scientists have likened their hunting technique to that of the cheetah, according to researchers in the Journal of Animal Ecology.

Their findings may dispel the common notion of whales as large slow creatures.

The research is the first to document the remarkable "burst-speed" of the pilot whale.

"As far as we know, no other whale has been recorded to swim nearly as fast at depth," says marine biologist Natacha Aguilar Soto, of La Laguna University in Tenerife, Spain.

"Short-finned pilot whales seem to be the greatest burst-speed athletes of the deep-diving mammals."

Overall, 23 pilot whales were tagged off the coast of the Canary Islands, which is one of three permanent residences of the short-finned creatures.

Mark Johnson of Woods Hole designed the tags to document the speed, depth and direction of the whales' quick dives. Sounds were also recorded.

During the dives, the acoustic tags revealed that the whales switched from slower echolocation clicks to a fast series of clicks, or buzz.

"The analogy is like going from snap-shots to video," he says, indicating the whales are trying to capture prey after the sprints.

Tags proved that it only takes 15 minutes for a pilot whale to dive over half a mile, and more, reaching speeds of 20 miles per hour as they instantly race toward their prey as soon as they spot it.

Until now, researchers assumed that deep-diving whales moved relatively slowly, due to the need to conserve oxygen whilst holding their breath.

"It was completely unexpected that short-finned pilot whales sprint at depth with limited oxygen reserves. Cheetahs, for example, more than double their breathing rate during chases," says Aguilar Soto.

However, whales are able to achieve such high speeds while holding their breath. Scientists say this may be why whales are often seen moving slowly on the ocean's surface. They could actually be catching their breath after a recent high-speed chase.

As for the size of prey, Aguilar Soto says they "must be large or calorific to reward the deep dives, and they must be able to move rapidly given the top speeds we clocked for the whales."

This led researchers to think that one creature in particular may be high on the whale's preferred menu: the giant squid Architeuthis.

"We found a piece of fresh Architeuthis arm floating in the vicinity of diving pilot whales and findings of bitten Architeuthis are common in the area where the whales live," Aguilar Soto said.

Pablo Aspas took a recent photo of a plot whale with a piece of a large squid in its mouth.

"Its color and the shape of the cups indicate it may well belong to Architeuthis and the size of the piece indicates that the full length of the tentacle would be more than two meters, corresponding to a squid 4-5 meters long and some 180kg in weight," says cephalopod expert Angel Guerra of the Institute for Marine Investigations in Vigo, Spain.

"We have imagined battles between sperm whale and giant squid. But it may turn out that it is pilot whales, one-third the size of sperm whales, which are sprinting for the giant squid!" Aguilar Soto said.


On the Net:

Journal of Animal Ecology