Our seas are getting louder, and in an effort to be heard over the noise of commercial, naval and recreational shipping traffic, oil installations, wind farms and the like, whales have had to raise their voices.
Marine biologists monitored 14 North Atlantic right whales in the Bay of Fundy, Canada, which is an area with a high level of human-generated noise in the form of shipping traffic, resulting in a chronic noise that overlaps the frequency range of right whale communication signals.
They found that as the background noise level rose, so did the whale's voices - in fact two of the whales in a particularly noisy area, were practically shouting.
Having to shout to be heard obviously uses up more energy for the whale, but there's also a chance that it distorts the sound of the call to other whales.
It's also been found that whales are gradually changing the frequency of their calls - it's now about an octave higher than it was in studies carried out in the 1950s
Sound is vital to whales. They use it in communication, navigation and feeding. Researchers are worried that increased noise levels may force whales to stay closer to one another, where their calls can be heard. This will reduce the area in which they breed and find food.
For more information see the paper: Susan Parks et al (2010). Individual right whales call louder in increased environmental noise. Biology Letters.