Marine biologists working in Massachusetts waters noticed that humpback whales sang less during the fall of 2006, when a low frequency signal showed up in their recordings. They eventually traced the signal to some acoustic sensing equipment that was part of a scientific study off Maine’s coast, about 120 miles from where they were studying seasonal changes in whale songs in Georges Bank.
The scientists recorded more frequent whale vocalizations (listen below) during the same time of year in 2008 and 2009, when the study’s Ocean Acoustic Waveguide Remote Sensing equipment was not being used. This suggests the whales reacted to the low-level sounds by silencing their songs.
“It’s fascinating that we saw this behavioral response over such a large distance,” said Denise Risch, a marine biologist at the National Oceanic and Atmospheric Association and lead author of research published Jan. 11 in PLoS One.
Previous research suggests that nearby underwater noise from ships, airguns, underwater explosions and sonar may cause hearing damage and changes in feeding, mating and communication among marine mammals. But this is the first time whales have been reported reacting to man-made sounds from so far away.
Whales are extremely social creatures with a remarkable ability to play with sounds. When a male humpback starts to sing, it may keep going for weeks at a time, says Christopher Clark, the director of the Bioacoustics Research Program at Cornell University. Clark, who was not involved in the study but has collaborated with the researchers, studies various species of whales in Mexico and Hawaii.
In mating grounds, males sing to attract the ladies and show off to other males, but scientists don’t yet know why they sing in feeding grounds like the ones in Georges Bank.
That the artificial acoustic signals, which Clark compared to the sound of a penny whistle, changed the singing behavior of these animals was “pretty dramatic” and a cause for concern because underwater technologies that use acoustics to transfer data are becoming more commonplace.
“It’s important to be concerned about the whales, but it’s also important to get it right,” said mechanical engineer Nicholas Makris, director of the Laboratory for Undersea Remote Sensing at MIT. Makris was monitoring herring on Geroges Bank in the fall of 2006 with the same acoustic sensing equipment Risch’s team detected near Massachusetts.
The researchers don’t know how many whales visited Georges Bank in 2006 when they heard the acoustic monitoring pulses, nor in 2008 and 2009, the two years they used for comparison. Whale populations can vary dramatically each year due to weather conditions and the availability of the herring the whales eat, Makris said.
While underwater noise is “not killing the whales or driving them up on beaches,” Clark said, “it’s man-made junk in the water. We haven’t been good neighbors on that front.”
Listen: Song of a humpback whale