Tuesday, October 18, 2011

Orcas make waves to hunt seals

Naturalists and guests on a National Geographic Expeditions cruise in Antarctica witness and record the phenomenon of Type B Orcas working in unison to dislodge a seal from an iceberg.

From BBC

A BBC film crew has captured footage of killer whales working together to create waves to wash their vulnerable prey into the water.
The predators targeted a weddell seal that was resting on a small ice floe, sweeping it off the ice to where they could attack it.

Scientists who worked with the film crew said the footage revealed new insights into killer whale ecology.
The team filmed the sequence for the BBC documentary Frozen Planet.

Robert Pitman, from the National Marine Fisheries Service in California, joined the team in order to carry out research and as a scientific adviser on the documentary.
He said that the footage was "some of the most amazing wildlife footage ever taken".
Although killer whales - otherwise known as orcas - had already been recorded hunting in this way, Dr Pitman said that "to see footage of it in action like that is totally unprecedented".

Wave-washing killer whales were first observed by scientists in the early 1970s.
"It wasn't seen again for about 30 years," explained Dr Pitman. "Then a tour boat saw it and [a tourist took] some home video.
"[The BBC] contacted us because they were interested in filming it.
"As part of our research, we're able to tag them [with tracking devices] and follow them," he explained.

Killer whales often work in teams to hunt seals, according to scientists from the National Oceanic and Atmospheric Administration in California.
Working together, killers whales create waves with their tails.
These waves in turn knock seals off their ice flows and into open water, where they are vulnerable.
But if the seal happens to hide among the ice after being knocked into the sea, the whales create shock waves with their tails or blow bubbles under the seal to chase their prey out into the open.

So, in 2009, Dr Pitman and his colleagues joined the BBC team off Adelaide Island, in the western Antarctic Peninsula, and went in search of wave-washing killer whales.
They are not the easiest mammals to track down; killer whales can travel up to 200 miles (320km) in a day as they move around in search of their prey.

"But we lucked out," recalled Dr Pitman.
"We saw 22 wave-wash attacks on 22 different seals; it turned out that this was actually a fairly common occurrence."

Dr Pitman said that the trip generated new insight into killer whale ecology.
"It was shocking to us that, although there are lots of different types of seals down there, they were only interested in weddell seals," he said.
"We learned a lot; it was a great collaboration."

The trip also added weight to a theory that there are actually several different types of killer whale.
Dr Pitman believes that there could be four different species in Antarctica alone and that their feeding habits are different - with some hunting mammals and some feeding only on fish.
"This is one of the world's most immediately identifiable mammals," he said, "and yet we're still discovering differences the species level."
"It just shows how little we know about the life in our oceans."

Links :
  • YouTube : Orcas hunting seal on ice floe in Antarctica

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