By Brian Fitzgerald

With a $789,000 grant from the U.S. Department of Defense, two College of Engineering professors are studying the auditory function of the world’s largest animals. Their aim is not just to save the whales’ hearing. They are trying to save their lives.

Man-made noise in the ocean, from supertanker propellers to sonar, may cause acoustic trauma, which many scientists say leads to mass strandings. When the sound levels are high enough to cause extreme discomfort, they believe, some whales respond by panicking. Last year, for example, 14 of the marine mammals beached and 8 of them died in the Canary Islands. In 2000, the same thing happened in the northern Bahamas, with 17 strandings and 7 deaths. Both events coincided with naval exercises.

In one sense, the cause of the strandings is no big mystery. The government of the Canaries pointed to Spanish naval sonar activity in the area, and the U.S. Navy admitted that sonar from its warships in the Bahamas contributed to the whale deaths there. What needs to be explained, however, is how certain types of sonar affect cetaceans, especially beaked whales, and why some sonar operations cause strandings, although most do not.
“Beaked whales are toothed whales,” says ENG Professor David Mountain. “And toothed whales are echolocators. That’s how they essentially see, and some Navy sonar, especially mid-frequency sonar, may interfere with their echolocation.

“It could partially ‘blind’ them,” he says. “I compare the effect to someone walking down a dark hall while a strobe light is flashing. It may disorient them.”

Receiving funding from the U.S. Navy, Mountain and colleague Allyn Hubbard are working on models of whale auditory function to better understand how susceptible the animals are to these sounds. Mountain, a biomedical engineering professor, and Hubbard, a professor of electrical and computer engineering, have also participated in several conferences in the past two years to discuss the processes that could cause apparently healthy beaked whales to become confused and head for land.

Beaked whales, so named because of their long, narrow snout, seem particularly vulnerable to the standard mid-frequency sonar used by NATO countries to look for enemy submarines. “The sonar may also contribute to lower populations of the species because it might be altering their feeding habits and reproductive success,” says Mountain.

Biomedical Engineering Professor David Mountain and student Brian Miller (ENG '03) with a large-scale model of a dolphin's hearing system.

“Normally, when we talk about acoustic trauma, we are concerned with dysfunction of the sensory cells within the inner ear,” he says. This function can be temporary, an acute condition called temporary threshold shift (TTS), or permanent, a chronic condition called permanent threshold shift (PTS). “TTS is what most of us have experienced after exposure to loud music or working with a chain saw without hearing protection,” he says. “TTS isn’t something that can easily be identified without behavioral or electrophysiological testing, and these techniques aren’t very practical for stranded or dead animals. PTS can be identified anatomically, but only if the tissue is very well preserved, a condition that is not usually met with stranded whales.”

Also, there is still much to learn about beaked whales, the least-known cetacean, and how sonar affects them. “They have no external hearing parts, so we don’t know how sounds get into the inner ear,” says Mountain. Complicating matters is the fact that beaked whales are reclusive and “usually remain far offshore—very few people have seen them.” However, because the Bahamas stranding was reported quickly, two of the six beaked whales were in good shape for a necropsy, or animal autopsy.

Mountain and Hubbard work with Darlene Ketten, an auditory specialist at the Woods Hole Oceanographic Institution who helped conduct the necropsies and anatomical studies on the whales in the Bahamas, as well as on other suspicious cases. The Boston University professors, with their students and laboratory staff, are making mechanical measurements and creating computer models of the whales’ hearing systems. Their research will help predict the whales’ hearing sensitivity to sonar and provide information for determining which combination of factors is most likely to cause another mass stranding.

“The Marine Mammal Protection Act states that these animals can’t be harassed or injured,” says Mountain, “so the Navy funds this type of project, along with studies on the migratory habits of the whales, to avoid injuring the animals when they plan major exercises.”
The Navy will review the research and implement measures to ensure fewer adverse effects on beaked whales when it uses tactical midrange sonar. “Marine mammal strandings are not unusual, and the overwhelming majority of these strandings are not correlated with any known human activity,” says Mountain. “The beaked-whale strandings have attracted attention because these species are much less likely to strand than other species. In the case of the mass beaked-whale strandings, as many as a third of them may be associated with naval activity. To me, the mystery is why beaked whales seem to be responding badly to conventional mid-frequency naval sonars, while other species don’t appear to be showing this behavior.”

Mountain, teaching at BU since 1979, has always been interested in research that combines engineering and neuroscience. He says that the Navy, “in the interest of national security, certainly won’t stop using these types of sonar during wartime—it’s their bread and butter. But in peacetime, when it’s used during training exercises, they have some leeway.” He finds it gratifying to be helping to better protect the beaked whale. “It’s an interesting whale to study,” he says. “It can dive extremely deep, and its hearing works under extremely high pressure. It’s a fascinating animal.”