Susan Parks has been fascinated with whale sounds since she first heard a recording of them at age 12. “It was like listening to someone speak a foreign language,” she remembers. “I wanted to know what they were saying to each other.”
Scientists believe that whales vocalize to locate one another, find mates, socialize, and hunt. Today, Parks, a research associate in Penn State’s Applied Research Laboratory, is investigating the possibility that some whales are changing their tune—specifically, the acoustic frequency at which they communicate—as a direct consequence of commercial shipping in waters near their feeding and migration routes.
Her current focus is on right whales, a species of baleen whale, the group characterized by comb-like plates in place of teeth for filtering food. (The baleens include the famous humpback as well as the great blue whale, largest of living creatures.)
Right whales, she explains, produce sounds ranging from about 50-200 hertz, a low-frequency range just at the lower end of human hearing, which overlaps with noises produced by ship propellers in the range of 100 hertz or less.
There has always been background noise in the oceans. However, chronic noise pollution, caused primarily by commercial shipping and other human activities, has grown exponentially in recent years. Researchers at Cornell suggest it is doubling every decade, pointing out that comparable industrial noise levels on land would require headphones to protect our ears. “A blue whale born in 1940 has had his acoustic bubble shrunken from 1,000 miles to 100 miles because of noise pollution” over the course of his lifetime, Cornell marine biologist Christopher Clark told the online publication LiveScience in 2005. (Blue whales can live for 100 years.)
In an increasingly noisy ocean, how are whales adapting? Parks and her colleagues conducted acoustic research on two closely-related species, North Atlantic and South Atlantic right whales, and found that they had shifted communications to a higher frequency. The shift, they say, corresponds to the increase in shipping traffic and the resultant background noise.
After conducting her own research on the North Atlantic right whale in Canada’s Bay of Fundy, Parks compared recordings of North Atlantic and South Atlantic right whales from 1956 and 1977 with similar recordings made between 2000 and 2004. She reported her results in a paper coauthored by Clark and Peter Tyack of the Woods Hole Oceanographic Institution, which appeared in the Journal of the Acoustical Society of America in 2007.
When comparing North Atlantic right whales over time, “the calls from 2000 were approximately two-thirds of an octave higher than the average values in 1956,” Parks confirms. She observed a similar change between 1977 and 2000 in the South Atlantic whales.
During a research project planned for September 2009, Parks hopes to gather additional evidence of this shift in frequency, and also to find out how quickly individual whales may make the change. For this study, she will monitor right whales from two adjacent bays in Argentina—one with heavy shipping traffic and the other a protected site—and compare the frequencies at which they communicate. To determine frequencies, Parks will tag whales with recording devices mounted on suction cups. Explains Parks, “This way we can hear what the whales hears, as well as the sounds they make.” Bottom-mounted archival acoustic recorders in both bays will monitor background noise.
“Since it is the same population of whales at the same time of year in the same weather conditions,” she explains, “I hope to be able to tease out the effects that shipping noises are having on calling behavior.”
Susan Parks, Ph.D., is a research associate in the Environmental Acoustics Program at Penn State’s Applied Research Laboratory. She can be reached at 814-865-7683 or sep20@psu.edu.
Marissa McCauley is a senior in the College of Liberal Arts. She is majoring in English with a minor in Earth Systems and was an intern for Research/Penn State in Spring 2008.