Amusing Web: Blainville's beaked whales avoid predators by maintaining silence near sea surface

Tuesday, July 26, 2011

Blainville's beaked whales avoid predators by maintaining silence near sea surface

Last updated at 4:52 PM on 26th July 2011

They are among the most mysterious animals which man has ever studied.

But now Blainville's beaked whales have surprised researchers once again - after they discovered they have 'stealth' mode.

The mammals do not communicate with each other when near the surface so that they cannot be found by predators.

Once they get to within 170metres of the water's surface there is no talking at all, even though such a climb typically took 19 minutes.

Full of surprises: Blainville's beaked whales do not communicate with each other when near the surface so that they cannot be found by predators

This is also in spite of the fact that the whales spend 60 per cent of their lives in waters above the 170metre cut-off.

During their research, the scientists recorded sounds made at the deepest depth ever recorded by a mammal - some 900 metres.

The team got their results by attaching suction cups with listening devices to eight whales and monitored them for a total of 102 hours, BBC Nature reported.

The researchers discovered the 170metre cut-off even though whales would need to communicate with other at such a depth for a number of social and familial reasons.

Such radio silence was essential however to avoiding killer or orca whales which swim in shallow waters and pick off prey - including other whales.

Below 450metres where they were safe the beaked whales were a lot more communicative, and the researchers recorded regular whistles and clicks which they called 'rasps'.

Such noises, which are thought to help with navigation, had never before been recorded.

There are 21 species of beaked whales and they are known as the deepest divers in the world having been tracked to depths of 1,899metres.

But little is known about them and there are thought to be more species which have not even been discovered because they remain in the depths, away from mankind.

The research was carried out by Natacha Aguilar of La Laguna University in Tenerife, Spain.

Also assisting on the project were colleagues at the Woods Hole Oceanographic Institution in Massachusetts in the U.S. and Aarhus University in Denmark.

'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,' they wrote in the study.

The findings were reported in the journal Marine Mammal Science.