By Victoria Gill

Science reporter, BBC News, Portland



Sperm whales may team up and hunt collaboratively, scientists have suggested. A US research team used hi-tech tags to glimpse some of the giant marine mammals' remarkable hunting behaviour. This tracking showed how the whales travelled together in groups, but when they hunted, each whale "varied its role" within the group. The research team announced the findings at the Ocean Sciences meeting in Portland, Oregon. Professor Bruce Mate from the Hatfield Marine Science Center in Oregon led the study. It may be that each individual takes it in turns to do the most physiologically demanding task

Professor Bruce Mate, Hatfield Marine Science Center Please turn on JavaScript. Media requires JavaScript to play. "The unique thing about this study is this new piece of equipment," he explained. "We have [a tag with] GPS precision for the whales' movements and a time and depth record of their dives. "And, for the first time, we have tagged several animals within the same group." Professor Mate showed tracking evidence of the whales sticking closely together over several months - swimming around the Gulf of Mexico. But as the huge mammals made their dives - hunting squid at depths reaching more than 1,000m - their behaviour varied with each dive. "We can see that they're actually changing their role over time," he said. "And we're speculating that the animals are herding a ball of squid." He said that 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. "It may be that each individual takes it in turns to do the most physiologically demanding task - the deep dive," he said. Professor Hal Whitehead, a researcher from Dalhousie University in Nova Scotia, Canada, who studies whales, was impressed by the data, but said the suggestion that whales might be herding a ball of squid may be a little "far-fetched". However, Dr Mate pointed out that previous research had shown this type of herding behaviour in dolphins. In that case, scientists were able to capture footage of the dolphins herding a ball of fish, and appearing to take turns to dive through the ball for a mouthful. Dr Mate explained that, with sperm whales, which dive to great depths, it was far more difficult to capture the behaviour. "Our next step will be to image the squid at the same time as tracking the whales," he said. "And to tag more members of the same group so that we can track their movements." The American Geophysical Union's Ocean Sciences meeting in Portland, Oregon, runs all week.



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