For the first time, scientists have temporarily captured baleen whales and tested their hearing, a controversial move that brings researchers closer to understanding how some of the largest and most intelligent animals on Earth perceive their world.
In 2023, researchers captured two young minke whales off the coast of Norway, applied gold-plated electrodes with suction cups to their skin, and then examined their brain waves while different sound frequencies played. Each young whale was at least 3 meters long and weighed about 1 tonne.
The results of the study, published Thursday in the journal Science, surprised whale researchers because they suggest the creatures can hear at much higher frequencies than expected. The mammals’ ability is far greater than that of the typical human, the research suggests.
“It was a little shocking,” said Dorian Houser, director of conservation biology at the National Marine Mammal Foundation and lead author of the study. “They have ultrasonic hearing, which we think is likely related to avoiding the orca as a primary predator, because they use echolocation signals to hunt their prey on the same frequency.”
The surprising findings come amid growing concerns about the effects of ocean noise from sources such as marine sonar, oil and gas exploration and ship traffic, which can change the behavior of marine mammals, cause hearing loss and even kill them. The new information could change which noisy activities in the ocean are allowed under the Marine Mammal Protection Act or lead to restrictions on certain equipment.
“There may be higher frequency sounds arising from ocean exploration activities that were never considered a potential problem for baleen whales that need a second look,” said Susan Parks, a professor of biology at Syracuse University in New York, who was not involved was. in the study.
This study also closes a chapter of great disagreement within the whale research community. Scientists had never captured baleen whales and tested their hearing before, because the animals are so large that it could be dangerous for both the whales and the researchers.
Some scientists and activists strongly opposed the four-year research effort – called the Minke Whale Hearing Project – over concerns that whales would become stressed and possibly die during their short stints in captivity. They argued that it was not possible to safely capture the whales or ensure that they would not develop long-lasting stress responses.
The Whale and Dolphin Conservation, a global non-profit organization focused on protecting these animals, organized and sent an open letter from scientists and veterinarians to the Norwegian government in 2021, urging that the project “be halted because it could cause significant trauma to the whales were targeted, without contributing to useful science.”
What the largest whales on Earth could hear has long remained a mystery to scientists. Because baleen whales – of which there are 16 species, including humpback whales, blue whales and fin whales – are too large to study in captivity, biologists have had to infer their hearing abilities from research into whale behavior, the way other animals interact with them and from models of their anatomy.
Scientists know from recordings and other observations that baleen whales rely on hearing for social communication and that this is important for their survival. Humpback whales sing complex songs related to courtship and mating, for example making ‘clicks’ while foraging.
“To actually get a direct measure of hearing, that was something that was kind of a holy grail,” Houser said.
Minke whales were a good target for audio testing because they are the smallest baleen whales and a species that hearing scientists don’t understand very well.
“For minke whales, I don’t think there’s a lot of detail about how they use sound on a day-to-day basis,” Parks said, adding that there are other baleen species “where we’re just linking species to sound.”
To conduct the tests, researchers at the Minke Whale Hearing Project devised a complex trap near Norway’s Lofoten Islands to capture whales, relying on the species’ predictable migration path along the coastline.
The researchers set up more than a mile of nets to guide the whales to a channel between two islands and then blocked their exits with barrier nets. The researchers then gathered the whales into a pre-existing fish farm, where they used a “hammock”-like net to pull the creatures closer to the surface.
In June 2023, the researchers captured two young whales and, working with on-site veterinarians, conducted 30 minutes of testing on one whale and 90 minutes on the other before releasing them. The researchers attached electrodes for brainstem monitoring, took blood samples and attached satellite tracking tags to monitor the animals’ behavior and well-being.
Houser said the effort required about 20 tons of nets and 12 to 15 people working around the clock to gather, monitor and test the whales. Although the whales’ blood sugar levels rose and their heart rates changed, he said they tolerated the tests well and continued their typical behavior afterward.
“These satellite tags show that they are becoming minke whales again,” he said, adding that the animals’ welfare was the researchers’ top priority.
A minke whale that was never captured or tested died when it became entangled in a net and drowned after a storm forced the research crew out of the water and loosened an anchor securing the nets.
Regina Asmutis-Silvia, executive director of the Whale and Dolphin Conservation of North America, said the organization remains opposed to the project.
“Releasing the whales alive does not mean that these individuals will not experience prolonged stress responses to sounds or activities they associate with this experiment and that their lives and health may be at risk,” Asmutis-Silvia wrote in an email. adding that it was “tragic and ironic to harm individual whales to substantiate how harmful human noise is to these species.”
Asmutis-Silvia said that similar science could have been completed by non-invasive means, such as research on behavioral responses or stress hormones, and that the science produced by the project had significant limitations.
“This is a sample size of two young male minke whales from a given region, so it’s not clear how this translates more broadly to other age classes in that area, let alone to other species,” she said.
Brandon Southall, a scientist and consultant who helped develop acoustic exposure criteria for marine animals for federal regulators, said he thought the research would help set future limits on ocean noise to keep marine mammals healthy.
“They did everything according to best practices, carefully and professionally. The fact that it has produced initial results and provided direction for conservation outcomes, I think on balance it has been useful and informative,” Southall said.
Southall said the new research did not measure the lowest levels of the whales’ hearing ability, which is more challenging because of the way neural signals work in the animals’ bodies.
He said low-frequency sounds, such as ship propellers or pile driving on the seabed for wind farms, travel long distances in the ocean and are more likely to cause damage to marine mammals.
“We need to think, before anyone does another study like this, what else can we get out of it,” Southall said.
Houser agreed that it is more difficult to study low-frequency sounds. But he said researchers had not yet reached the lower limit of the signals they could detect. He said the Minke Whale Hearing Project has been put on hold, but he would like to explore the subject further if he could secure funding.
This article was originally published on NBCNews.com
