In a contentious move that advances our knowledge of how some of the biggest and smartest creatures on the planet view their surroundings, scientists have temporarily trapped baleen whales and tested their hearing for the first time.
Researchers caught two young minke whales off the Norwegian coast in 2023, used suction cups to apply gold-plated electrodes to their skin, and then watched their brain waves as various sound frequencies were played. Each baby whale weighed roughly one ton and was at least twelve feet in length.
Whale researchers were taken aback by the study’s findings, which were released Thursday in the journal Science and indicate that whales are capable of hearing at far higher frequencies than previously thought. According to the research, the mammals’ abilities are significantly superior to those of average people.
Dorian Houser, the principal author of the study and director of conservation biology for the National Marine Mammal Foundation, described it as quite startling. Since they employ echolocation signals to seek their prey at the same frequencies, we believe that their ultrasonic hearing is likely related to their ability to evade the killer whale as a primary predator.
The startling results coincide with an increasing awareness of how ocean noise from sources such as ship traffic, oil and gas exploration, and navy sonar can change the behavior of marine mammals, impair their hearing, and even kill them. According to the Marine Mammal Protection Act, the new findings may change what noisy activities are permitted in the ocean or result in equipment limits.
Susan Parks, a biology professor at Syracuse University in New York who was not involved in the study, claimed that there may be higher frequency sounds generated by maritime exploration activities that were never thought to be a possible issue for baleen whales and therefore require further investigation.
A period of intense debate within the whale research community is also resolved by this work. Because baleen whales are so huge, it could be harmful for both the whales and the researchers to capture them and test their hearing.
Concerns that whales might experience stress and maybe perish during their limited periods in captivity caused several scientists and environmentalists to strongly oppose the Minke Whale Hearing Project, a four-year study project. They maintained that there was no way to securely catch the whales or guarantee that they wouldn’t experience chronic stress reactions.
In 2021, the international nonprofit advocacy group Whale and Dolphin Conservation, which works to protect these animals, organized and sent the Norwegian government an open letter from scientists and veterinarians urging the project to be halted because it might cause significant trauma to the targeted whales without advancing scientific knowledge.
Scientists have been wondering for a long time what the biggest whales on the planet might hear. Because the 16 species of baleen whales—including humpback, blue, and fin whales—are too big to study in captivity, scientists have had to make assumptions about their hearing capacity based on behavioral research, interactions with other animals, and anatomical models.
Due to recordings and other observations, scientists are aware that baleen whales depend on their ability to hear for social communication, which is crucial to their survival. For example, humpback whales click when foraging and sing intricate songs related to courtship and mating.
“That’s been kind of a Holy Grail to get an actual direct measure of hearing,” Houser added.
Since minke whales are the smallest baleen whales and a species that hearing scientists don’t fully understand, they were an excellent target for audio testing.
“There are other baleen species where we’re just matching species to sound,” Parks said, adding that “I don’t think there are a lot of details on how they use sound on a daily basis for minke whales.”
Based on the whales’ predictable migration route along the coast, the Minke Whale Hearing Project researchers developed a sophisticated trap to catch whales in the vicinity of Norway’s Lofoten Islands.
After guiding the whales into a passage between two islands with more than a mile of nets, the researchers used barrier nets to block off the animals’ escape routes. The whales were then herded into an existing fish farm enclosure, where the researchers deployed a net that resembled a hammock to draw the animals closer to the surface.
Two baby whales were captured by the researchers in June 2023, and before releasing them, they were tested for 30 minutes on one and 90 minutes on the other by on-site vets. To monitor the behavior and welfare of the animals, the researchers inserted satellite tracking tags, collected blood samples, and connected electrodes for brain stem monitoring.
In order to corral, monitor, and test the whales, Houser said the endeavor took roughly 20 tons of netting and 12 to 15 workers who worked around the clock. He claimed that despite the fact that the whales’ heart rates and blood sugar levels fluctuated, they handled the tests well and carried on with their usual behavior.
He added that the wellbeing of the animals was the researchers’ first concern and that “those satellite tags do show that they return to being minke whales again.”
After a storm pulled the research crew off the ocean and dislodged an anchor securing its nets, a minke whale that was never captured or studied drowned after being trapped in a net.
The organization is still against the idea, according to Regina Asmutis-Silvia, executive director of the Whale and Dolphin Conservation in North America.
The whales’ lives and health may be jeopardized if they are released alive because this does not guarantee that they will not experience long-term stress reactions to noises or activities they associate with this experiment. “It is tragic and ironic to harm individual whales to substantiate just how harmful human sounds are on these species,” Asmutis-Silvia remarked in an email.
According to Asmutis-Silvia, the project’s science had major limitations and comparable research might have been done noninvasively, for as by examining stress hormones or behavioral responses.
“It’s unclear how this translates more broadly to other age classes in that area, let alone other species,” she said, citing the sample size of two immature male minke whales from a specific region.
According to scientist and consultant Brandon Southall, who has assisted federal regulators in creating acoustic exposure standards for marine species, he believes the study will help establish future ocean sound restrictions that would protect the health of marine mammals.
They carried out every task with care, professionalism, and adherence to best procedures. Overall, I believe it was helpful and educational because it did produce the initial findings and it directs conservation outputs, Southall stated.
According to Southall, the new study did not assess the whales’ lowest hearing ranges, which is more difficult given how brain signals function in animal bodies.
According to him, marine mammals are more likely to be harmed by low-frequency noises that travel long distances in the water, such as ship propellers or seafloor piledriving for wind farms.
Before someone conducts another study like this, we should consider what else we might learn from it, Southall added.
Houser concurred that studying low-frequency noises is more challenging. However, he said that scientists were still able to identify signals below the lower limit. He stated that the Minke Whale Hearing Project is now on hold, but if he could get funds, he would like to look into the matter more.
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