Shhh! Shallow stealth tactics of beaked whales
Orcas swim and hunt much closer to the surface
At depths below 450m, the whales made a series of echolocation clicks, interspersed with so-called buzzes, tonal whistles and short bouts of repeated clicks.
The whales likely make the echolocation clicks to navigate and hunt prey.
But the whistles and repeated clicks, which the researchers dubbed “rasps”, had never been recorded before.
These could serve to help the whales co-ordinate their movements as they disperse at the bottom of a dive to hunt.
The researchers believe that entering a stealth mode when swimming in shallow waters is an anti-predator strategy.
Killer whales, more appropriately known as orcas, are shallow divers that prey on many whale species in shallower waters.
By swimming in stealth mode, the beaked whales avoid broadcasting their location to orcas.
Hiding in the oceans this way may be an effective avoidance strategy, as beaked whales cannot out-swim orcas and have few other defences against them.
“For Blainville's beaked whales that live in cohesive associations and co-ordinate their activities, keeping silent near the surface is an unexpected behaviour and strikingly in contrast with that of other toothed whales,” the researchers write in the journal.