Imagine a frog call, but with a metallic twangand the intensity of a chainsaw. Thats the boing of a minke whale. And its a form of animal communication in danger of being drowned out by ocean noise, new research shows. By analyzing more than 42,000 minke whale boings, scientists have found that, as background noise intensifies, the whales are losing their ability to communicate over long distances. This could limit their ability to find mates and engage in important social contact with other whales. Tyler Helble, a marine acoustician at the Naval Information Warfare Center Pacific, and colleagues recorded minke whale boings over a 1200-square-kilometer swath of the U.S. Navys Pacific Missile Range Facility near the Hawaiian island of Kauai from 2012 to 2017. By measuring when a single boing arrived at various underwater microphones, the team pinpointed whale locations to within 10 to 20 meters. The researchers then used these positions, along with models of how sound propagates underwater, to calculate the intensity of each boing when it was emitted. The team compared these measurements with natural ambient noise, including waves, wind, and undersea earthquakes. (No military exercises were conducted nearby during the study period.) They found that minke whale boings grew louder in louder conditions. Thats not surprisingcreatures across the animal kingdom up their volume when theres background noise. (This phenomenon, dubbed the Lombard effect, holds true for humans, toothink of holding a conversation at a loud concert.) But minke whales responses differ from those of other whales, the team found. Orcas and humpbacks seem to compensate fully for increasing noisethe intensity of their calls grows in lockstep with ambient noise levels. The calls of minke whales, on the other hand, increased only marginally in the presence of loud noise. Thats similar to the responses of bottlenose dolphins and even some terrestrial animals, such as bats and frogs. The minkes relatively quieter calls mean that population estimates of the small, elusive whalestypically conducted using acoustic surveysare probably inaccurate, the researchers suggest. The animals arent endangered, but very little is known about them, says team member Regina Guazzo, a marine ecologist at the Naval Information Warfare Center Pacific. Sound is the primary way whales sense and understand their environment. Helble and his colleagues estimate that minke whales calling in a relatively low-noise environment could be heard by others as far as 114 kilometers away; as noise levels increased, that range dropped to just 19 kilometers, they report this month in The Journal of the Acoustical Society of America. Its an order of magnitude change in communication range, Guazzo says. [Because] its hard to know how far they need to be able to communicate, this could have a really negative impact. The researchers say humanmade noisecaused by shipping activity or military exercises, for examplewould likely have the same effect as natural noise. Thats significant, as the ocean has been getting louder by roughly 3 decibels per decade, primarily because of commercial shipping. As prolific noisemakers, we have an obligation to limit the potentially harmful sounds permeating the ocean, says Cornell University marine ecologist Michelle Fournet, who was not involved in the work. If we start to understand where the inability to communicate kicks in, we can change our human behavior.
sciencemag.org, 18 February 2020