Friday, 14 June 2013

12 - Listening for whales

A whale, most likely a finwhale, passing by the RRS James Cook
The spout of a whale is one of the iconic images of the open sea, and it is one we have been lucky enough to see several times on this cruise. Such a sight is fleeting, however. The majority of a whale’s life is spent below the surface, with sperm whales known to dive as deep as 3km down into the ocean.

This makes it very difficult to do something as seemingly simple as to count how many whales there are in the sea. Given the vast expanses of the ocean, covering over two thirds of the Earth, even when they do surface it is very unlikely a ship will be there to see them and take note. So, if we want to study whales, we need a way to see underwater.

Two whales, one showing a flipper
Unfortunately, sunlight penetrates only a very short distance through water. However, sound can travel great distances. This is how whales themselves communicate, so maybe the thing to do is simply to listen in. To do this, the boffins at the Sea Mammal Research Unit of the University of St Andrews have been developing very sensitive underwater listening devices, called hydrophones. The ocean is a surprisingly noisy place though. Our current home, RRS James Cook, itself provides a constant background of engine noise that makes listening for distant whales like trying to hear a conversation in a crowded room. What is needed is a quiet place to put the hydrophone to eavesdrop on the whales. Cue Pelagra, the floating sediment traps we have been using to collect and study marine snow. These may provide an ideal platform. They hover silently on their own, hundreds of metres down in the water, away from waves and boats.

SMRU have very kindly lent us one of their detectors which, even now, is strapped to the side of Pelagra P8, heading westwards in an orderly manner, 200m below the surface. Tomorrow morning, P8 is due to pop up and be collected. Hopefully, we will then be lucky enough to hear whale sounds as well as see them.

By Adrian Martin

P.S.: The PELAGRA P8 has been recovered successfully this morning at around 06:00. And we were fortunate enough to find a short recording of a whale calling. (Opens new window - please close to return to this page)

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