Beluga whales pass first-ever marine mammal hearing test

Researchers had previously tested the hearing abilities of captive dolphins. Based on those results, scientists at the Woods Hole Oceanographic Institution expected to find greater levels of hearing loss among the beluga whales in Alaska's Bristol Bay.

To test the whales' hearing, marine biologists used a unique suction cup sensor to measure the whales' brain activity while playing a series of quiet tones.

"It's fairly straightforward," WHOI biologist Aran Mooney said in a news release. "We just had to make a portable system that we could bring out into an extreme environment in order to perform the hearing tests."

After measuring the hearing sensitivity of 26 beluga whales, scientists recorded natural soundscapes in Bristol Bay in order to better understand how the sonic environment might influence the whales' hearing.

Scientists published the results of their tests in a pair of papers, the most recent of which was published this week in the Journal of Ecoacoustics.

"In the first paper, we characterized the beluga population's hearing ability, which had not been done before in a healthy, wild population," Mooney said. "And in the second paper, we put that into context to see how they might use acoustic differences in their habitat and how their hearing is influenced by the natural ambient noise in their environment."

To catch the whales, researchers relied on the expertise of Alaskan Natives who hunt belugas. The team captured the whales in soft nets in the bay's shallows, being careful not to stress the whales. The whales remained calm and still during the tests. Belugas often rest quietly in the shallows when avoiding predators such as orcas.

Scientists compared the results of the hearing tests with similar tests involving captive dolphins. The results suggest hearing loss is less prevalent among belugas, perhaps due to their much quieter environment.

"Sensitive hearing within a quiet soundscape could allow belugas to detect predators, navigate, and communicate with their young via low-amplitude signals," Mooney said. "This hearing sensitivity could be compromised in a noisier environment. It also suggests management concerns for animals that inhabit noisy areas, where they may already be showing greater proportions of hearing loss."