Bad Vibes: Whale Song Vibrations May Be Distrupted by Human Activity

A new study from the Woods Hole Oceanographic Institution may have revealed a previously unknown element of whale songs: particle motion plays a vital part in their communication. Woods Hole Oceanographic Institution biologist Aran Mooney believes this may play a vital role in locating other whales in the open ocean.

In a paper published in the online journal Biology Letters, Mooney reports approaching a group of humpback whales off the coast of Maui, Hawaii. He and his team measured two components of the whales' songs: pressure waves (the type of sound wave that pushes on human eardrums, allowing us to hear), and particle motion (the physical vibration of a substance as sound moves through it). The extensive underwater particle motion surprised Mooney.

"We threw our gear over the side, and let ourselves drift away from whales while measuring both particle motion and sound pressure. We didn't expect particle motion to be projected much at all, just a few meters away at most. But as we got progressively further away, the particle motion stayed loud and clear," Mooney recounted. Data gathered by Mooney's group showed that the whales' particle motion, especially in lower frequencies of sound, could travel much further than the distance recorded. "It's a whole other avenue of sound that we never knew whales could use."

Detecting particle motion required sensitive underwater accelerometers, which had not been widely available to researchers until recent years. Mooney and his team, however, had this equipment on hand for an unrelated study in the area and were able to collect these unexpected recordings.

Since humpback whale ear bones are fused to the animals' skull, this could provide a direct link to any sort of vibration in the water column. "This could mean that their hearing is influenced by the way sound conducts through their bones," Mooney explained. "It raises the question: does a whale's lower jaw act like a tuning fork to direct vibrations to their ears? Previous papers have shown this bone conduction might be a viable mode of hearing."

But if whales could in fact sense particle motion as Mooney and his team discovered, the similar vibrations caused by humans might interfere with the way the giant animals communicate.

"Most human-made noise in the ocean low frequency, and the level of sound is doubling every decade. There's constantly more shipping, more seismic exploration for oil and gas," Mooney stated. Mining and construction, such as pile-driving machinery, is also increasing, resulting in low-frequency particle motion that might propagate for miles underwater. "We humans don't hear well in water, so we overlook noise in the ocean, but it's very relevant cue for marine animals," Mooney concluded. "This could be a major concern for whales."