The underwater world is a lot less quiet than you might imagine. Sound travels long distances through water, and there's plenty of sonic action on the ocean, especially from boat engines.

Scientists from England now report that whale-watcher boats may be creating such a racket that killer whales off the coast of Washington State are changing their calls to communicate with each other. The whales' actions are similar to the ways we adjust our voices to be heard in a noisy restaurant.

The study focused on three pods that live near the Washington coast. Each pod is a family unit that stays together for many years. The pods all have distinctive calls. One pod's call sounds like a train whistle. The second pod's call sounds like a mewing kitten. The third pod's call sounds like a slide whistle.

Pod members use the pod's signature call more than half the time that they communicate among themselves.

Researchers analyzed recordings of signature calls taken during three time periods: 1977 to 1981, 1989 to 1992, and 2001 to 2003. During the first two periods, the length of the whales' calls was the same whether or not there were boats around. In the most recent recordings, however, whale calls were 15 percent longer when boats were present.

Whale-watching tours have grown increasingly popular during the last decade. There are now five times as many boats clustered around whale pods as there used to be. All the noise the vessels make may be interfering with whale communication, some researchers fear, and harming the animals as a result. The population of killer whales has been shrinking since 1996.

It's not necessarily bad to go whale watching, experts say. But the activity may need to be regulated to cut down excess noise. This way, whale watchers will always have something to watch.—E. Sohn