The minke whale is a smaller species of whale
Kerstin Meyer/Getty Images
Brainwave testing of two young whales has revealed they can hear sounds at higher frequencies than previously thought, forcing researchers to rethink how the ocean’s largest animals respond to noise from predators and humans.
“This is truly pioneering work,” he says Susan Parks at Syracuse University in New York, who was not involved in the new study. “Measuring a wild whale’s hearing directly is something researchers in the field have been working on for decades…This is, to my knowledge, the first successful test of this method with a whale.”
But baleen whales include the largest animals on Earth, and the test method of temporarily holding a hearing test is not easy. “The whales’ body size is too large for the approach to be effective,” he says Dorian Houser at the National Marine Mammal Foundation, a non-profit organization based in California. So Houser and his colleagues turned to a species of whale called the minke whale.
The researchers studied the migration route of minke whales off the coast of Norway and found a natural channel between the two islands, where they used net fences and boats to guide the two whales – each about 3 to 5 meters long – to a fish farm enclosure. a drop-down web portal. The researchers then used a roller system to pull out a net and keep the juvenile animals partially submerged in the water’s surface.
In the hearing test, two gold-plated electrodes with silicone suction cups were placed on each whale’s skin near its snout and dorsal fin, which allowed the researchers to record brain wave signals. They measured how the whales’ brains responded to an underwater loudspeaker for about 30 minutes for one whale and 90 minutes for the other.
Such experiments revealed that whales’ auditory trunks respond to ultrasonic sounds beyond what the human ear can detect, at frequencies between 45 and 90 kilohertz – a wider hearing range than previously thought based on ear anatomy and vocalizations.
Banding and reducing wild marine mammals is “quite controversial” because the animals have the potential for “a lot of stress,” he says. Oliver Boisseau at Marine Conservation Research, a non-profit organization based in the United Kingdom. But he explained that the findings are “very important” in helping to understand how the whales can escape from predators such as killer whaleswhich hunt using high-frequency echolocation clicks.
Researchers should rethink how they affect whales military sonar and commercially available echoes are used to map the seafloor, says Boisseau. “It seems that the more we study marine mammal hearing, the more we confound our initial assumptions,” he says.
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