The oceans are getting louder and forcing some whale to speak up, according to a study published yesterday in the journal Biology Letters. Lead researcher Susan Parks of Penn State University eavesdropped on seven male and seven female North Atlantic right whales by attaching acoustic tags to them via suction cups. Each tag recorded from 2 to 18 calls, which included the whales' greeting "upcalls" (seemingly questioning "hmm?" sounds that go from a low to high pitch -- see video), as well as background noise--believed to come from commercial shipping. Bioacoustics researcher Christopher Clark of Cornell University, who did not participate in the study, says that ocean noise is becoming a serious issue.
"If I had to immerse you into the sea off Boston, you'd be shocked. You'd be like a country mouse dropped in the middle of Heathrow Airport," says Clark. "In one generation, we have raised the background level for an entire ocean ecosystem." [New Scientist]
At 400 hertz, some of this background noise seems to overlap with the frequency of right whale greetings, and Parks believes that these endangered whales are shouting to compensate. The team recorded background noise ranging from 92 to 143 decibels; whales seemed to respond by increasing the volume of their calls in line with the background noise, producing calls which ranged from 120 to almost 150 decibels.
"The impacts of increases in ocean noise from human activities are a concern for the conservation of marine animals like right whales," [said Parks].... "The ability to change vocalizations to compensate for environmental noise is critical for successful communication in an increasingly noisy ocean." [Penn State]
The study was small, only including fourteen whales, and therefore preliminary. Background noise levels vary depending on ocean location, and different whale species make calls at different volumes and frequencies. Still, if the noise in the oceans continues, the study's authors argue, the whales may have trouble making the calls necessary for activities such as feeding and mating.
One downside is that "shouting," as for humans and other animals, requires more energy expenditure and probable strain, so we are making life more difficult for these already at risk marine mammals.... "When noise exceeds a certain level, right whales will not be able to increase their call amplitude enough to compensate," [Parks said]. [Discovery News]
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