Southern Residents increasing length of calls when boat noise present

A scientific paper showing that over the last decade the Southern Resident orcas have lengthened their calls when vessel noise is present has been published in the science journal Nature. The Whale Museum's Executive Director Richard Osborne, Ph.D., was one of the authors.

The effect is called "anti-masking" behavior and is typical for birds and mammals trying to improve acoustic communication in a noisy environment, said Osborne, who worked with co-authors Andrew Foote and Rus Hoelzel of the University of Durham in England. The study states that the orcas' calls are about 15 percent longer in the presence of boats than when boats are absent.

"These findings simply mean that background vessel noise has reached a point where the whales are measurably compensating," said Osborne. "It is no different than what people do when they move a conversation from inside a building to a noisy street environment.

"What we have measured in the whales is simply this same effect. This has no direct energetic effects on the whales, or direct implications as to contributing to their decline. It means background vessel noise is noticeable enough to them that they compensate like any other mammal would in a noisy environment. The lesson for boaters is that we need to reduce underwater noise from all vesel traffic -- which can be done by slowing down in the spatial hearing range of the orcas."

Read the BBC article about this topic.

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