Whales
are social animals that like to keep in touch with each other. They have rather
low frequency voices that range below that of a human singing bass. The low
frequency sound carries for very long distances through water so that they can
communicate over long distances.
The
blue whales are one of our endangered species that live by sieving krill out of
the sea water. They call to one another to indicate good feeding conditions
with what are know as D-calls.
Unfortunately
for the whales, we humans are causing more and more noise pollution with ship
engine noise, explosions and powerful sonar. Melcón et al have followed a group of blue whales and monitored their
vocal behavior under various conditions of noise pollution (1).
The
general noise from passing ships is at multiple frequencies that are used by
the whales and the whale’s response is to shout louder so that their colleagues
can get the messages in spite of the noisy background. They also call more
frequently to ensure that the messages are received.
If,
as is their habit, the navy or the oilmen create explosions, the whales shut up
for a little while until they can get their act together and get back to
chatting in whale.
The
bad thing, though, is powerful sonar signals. They shut right up and keep mum.
Remember sonar is not broad-spectrum noise. We’re not very fond of piercing
narrow frequency sound as I’m sure you’ll agree if you remind yourself of some
alarm systems that can scare everybody off for miles around.
It
can’t be much fun for the whales and it seems that it can quite put them off
their feed. We should remember that noise pollution can be more than just
irritating and that other species use different frequency ranges from
ourselves. Whales are using low frequencies to get messages over huge
distances, while Tarsiers in the Phillipines are using high ultrasonic
frequencies that are outside the hearing of their predators and only travel
very short distances.
