August 2018 MAINE COASTAL NEWS Page 23. News From Woods Hole Oceanographic Institute Continued from Page 10.


impacts on animals and to management eff orts to mitigate sound-induced hearing loss.


In the two related studies, WHOI re- 9702


searchers and their colleagues measured the hearing sensitivity of 26 wild belugas and then compared the audiograms to acoustic measurements made within their summer habitat in Bristol Bay to study how natu- ral soundscapes—all sounds within their environment—may infl uence hearing sen- sitivity. The soundscape also reveals sound clues that the belugas may use to navigate. The fi rst study was published May 8, 2018, in the Journal of Experimental Biology. Results from the soundscape study were published June 20, 2018, in the Journal of Ecoacoustics. “In the fi rst paper, we characterized the


beluga population's hearing ability, which had not been done before in a healthy, wild population,” says Mooney. “And in the sec- ond paper, we put that into context to see how they might use acoustic diff erences in their habitat and how their hearing is infl u- enced by the natural ambient noise in their environment.” How do you test a beluga whale’s hear-


ing? Researchers applied the same screening method that doctors use to test the hearing of newborn babies who can’t yet vocally respond to whether or not they hear sounds: automated auditory brainstem response. A suction cup sensor is gently placed


on the whales’ head, just behind the blow- hole, and another is placed on the back for reference. A series of quiet tones are played, and the sensors help measure the brain's response to the sounds from the surface of the skin. “It's fairly straightforward,” Mooney


says. “We just had to make a portable sys- tem that we could bring out into an extreme environment in order to perform the hearing tests.”


The test itself goes quickly, taking only


about fi ve minutes to measure each frequen- cy. The most challenging part, says Mooney, is catching the participants. For that, the researchers relied on the


expertise of Alaskan Natives who hunt be- lugas. From small aluminum boats, the team would approach an individual adult whale— no calves were included in the study—in shallow waters of the bay. Taking care not to


stress or injure the whale, they would catch it in a soft net. Marine mammal handlers, including teams from Georgia Aquarium, Shedd Aquarium, and Mystic Aquarium, would then get in the water to help secure the animal’s tail with a rope before moving it to a belly band (like a small stretcher) in the water next to a soft infl atable boat where the hearing tests took place. “The belugas stayed relatively relaxed


during the tests, seemingly employing a resting behavior that they may use to avoid killer whales,” Mooney explains. “When a killer whale is hunting them, belugas will often move to very shallow water and qui- etly stay there until they can safely return to deeper waters.” In addition to the auditory testing,


the researchers also performed a physical exam to assess the overall health, sex, and estimated age of each animal and obtained skin, breath, and blood samples to collect information on the whales’ hormone levels, microbiome bacteria, and other health-re- lated data. The assessments were part of a beluga population health assessment pro- gram coordinated by the NOAA Fisheries Alaska Fisheries Science Center, the Alaska Department of Fish and Game, and Alaska SeaLife Center. Satellite transmitters were attached to some of the whales before release to study the whales’ movements. The hearing tests revealed little hearing


loss in the seemingly older members of the population, which could be because the es- tuary where the belugas reside is fairly quiet compared to more urban areas. “Because there haven't been any other studies of the hearing of wild marine mam- mals, we compared the results to previous studies of captive dolphins in San Diego and in Russia,” Mooney says. “The dolphins showed clear hearing loss as they aged, but the San Diego group lives in a very noisy environment, as most humans do.” Mooney and colleagues also compared


the wild belugas tests to those of belugas living in human care facilities. Both groups heard similarly well, and the authors suggest that it is likely due to the quiet environments in which they live. “Sensitive hearing within a quiet sound-


scape could allow belugas to detect preda- tors, navigate, and communicate with their young via low-amplitude signals,” Mooney explains. “This hearing sensitivity could be compromised in a noisier environment.


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It also suggests management concerns for animals that inhabit noisy areas, where they may already be showing greater proportions of hearing loss.” The two studies are important to eff orts


to evaluate the eff ects of underwater noise on endangered Cook Inlet beluga whales, whose numbers have dwindled to an es- timated 328. The species lives in habitats close to Anchorage, AK, and is exposed to noise from shipping, pile driving, con- struction, and explosive noise from nearby military bases. Project funding and fi eld support were


provided by Georgia Aquarium, the Marine Mammal Laboratory of the Alaska Fisheries Science Center, WHOI, NOAA Fisheries Alaska Regional Offi ce, U.S. Fish and Wild- life Service, Bristol Bay Native Association and Bristol Bay Marine Mammal Council, the Alaska Department of Fish and Game, Alaska SeaLife Center, Shedd Aquarium, and Mystic Aquarium. The Woods Hole Oceanographic Insti-


tution is a private, non-profi t organization on Cape Cod, Mass., dedicated to marine re- search, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment. For more information, please visit www.whoi.edu.


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