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Orcas against beaked whales : part of cache-cache between the giants of the seas

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This is perhaps the part of hide-and-seek the most impressive in the world. A sort of game of cat and mouse between species greater than 5 meters. Orcs against beaked whales, a clash of titans but a battle of balance. In direct contact, the seconds have no chance. Less fast, less powerful especially. Then they have developed a method that an international team was unveiled on Thursday 6 February, in the journal : stay grouped together, silent and never ascend vertically.

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“When we observed this behavior, it seemed to us initially to have no sense,” says Natacha Aguilar de Soto, marine biologist at The university of la Laguna, Canary islands (Spain). Usually, the other giants of the seas, such as the sperm whale, leave the youngsters and a few baby-sitters in shallow water when they dive for fish, and communicate with them by infrasound. Except that they are expressed in frequencies are often inaudible to the orc. And their mass allows them to fight collectively.

The northern bottlenose whale does not have this chance and is, therefore, quite the opposite. As soon as an orc approaches, the clan dives, with perfect coordination and in total silence. The acoustic signals through which these social mammals communicate, but also whose echoes allow them to locate their prey, is silent. They do rekindle that below 450 metres, out of reach of the killer. The group re-formed, the fishing season in full swing, at depths that can exceed 1,000 metres, in total darkness, so.

Sensors suction

But, after forty-five minutes of exercise, it is necessary to breathe. The group then picks a direction and goes back to, again in silence, with an angle of 55 degrees on average, which causes the emergence of more than 1 km from its starting point, away from the jaws of killer whales. We understand the importance of a dive with the juvenile and, in turn, why, of all the whales, this group is the one which has the small display, the relative weight the most important. The strategy has certainly had a cost : the scientists have amounted to 35 % of fishing time active lost. But it is the price of survival.

To achieve these results, the researchers first had to find beaked whales, cetaceans stealth if it is. They have found two species in the Canary islands, the Azores (Portugal) and off the coast of liguria (Italy), and were equipped with 26 individuals of sensors adhesives. A proven technique : at the end of twenty-four hours, the vacuum pads disengage, tape recorders back to the surface and deliver their sound data, and geographical.