In a noisy room, humans will yell to be heard, eventually giving up when communication becomes impossible. Now researchers have found that North Atlantric right whales, too, get louder in response to the noise level of their environment.
Left unanswered is what might happen when an increasingly noisy ocean becomes too loud for easy communication.
Monitoring 14 right whales — seven males and seven females — in the Bay of Fundy, Canada, researchers from Pennsylvania State University, Woods Hole Oceanographic Institute and Duke University found that the animals' call amplitude rose proportionately as background noise increased. Their study was published in the July issue of Biology Letters.
"Whales are compensating for increased ocean noise by going up in volume when they call to one another, which is basically the same thing that humans do when they're trying to talk in really noisy bars," said Joseph Gaydos, chief scientist for the SeaDoc Society at UC Davis, who was not involved in the study.
Previous studies had shown that numerous species of animals, including some whales, alter their call amplitudes in response to rising noise levels. This is the first study to show that right whales do this as well, expanding the number of species potentially affected by man-made changes in their auditory environment.
This is also one of the first studies to assess changes in whale calls as a response to increases in ambient noise, rather than increases in single-source noises.
The North Atlantic right whale is a type of baleen whale that is listed as an endangered species. Its primary habitat is in the coastal waters of the eastern United States and Canada, an area with high levels of commercial, naval and recreational shipping traffic, said Susan Parks, lead author of the study and assistant professor of acoustics at Pennsylvania State University.
Further, the noise generated from the commercial ships has the same pitch as a right whale's call, Parks said. "This is a problem because its noise source overlaps the frequency range of the whales' calls," she added.
Said Stephanie Watwood, a visiting biologist at Woods Hole Oceanographic Institution, who was not involved in the study: "Most of the focus previously has been on the effect of noise from intense sounds, like military testing or underwater construction, and this study focuses on the effects of lower, ambient level noises, which can affect a greater number of individuals in the environment for longer periods of time."
Sound is an important aspect of the right whales' survival because they rely on it for vital life functions, such as communication, navigation and feeding.
"All of these whales live in the world of Stevie Wonder," Gaydos said. "It's all about acoustics for them. Seeing is more difficult, so it's all about sound."
Researchers worry about the potential effect of increased noise pollution in the oceans. "Marine mammals are experiencing greater amounts of noise increases than many terrestrial animals, so it's important to understand how they respond to this and what the effects will be," Watwood said.
Unlike land animals, sea creatures can find it difficult to escape areas of loud ambient noise.
"It's kind of like what humans experience in bars," Gaydos said. "Some bars are so noisy that even when we yell, we can't be heard, so we don't go to them anymore. But what happens to whales when the noise level increases too much in their own environment? They have a harder time escaping that."
Increased noise levels could force the whales to stay closer to one another, thus shrinking the area where they mate and find food, researchers speculate.
Putting the whale dilemma in human terms, Gaydos said a college student who hung out only in noisy bars would never find a date.