A first for baleen whale science
No one had ever directly measured a baleen whale’s hearing. This four-year study produced the first measurements on record.
A surprising discovery
Minke whales can hear well into the ultrasonic range, higher than scientists predicted.
A tool for protection
The data are helping researchers and regulators understand which kinds of ocean noise may affect baleen whales, and how to reduce the risk.
Until recently, no one had ever directly measured what a baleen whale can hear. Scientists could only estimate it from ear anatomy and the sounds whales make themselves, a real gap given how much these animals depend on sound to survive. Over four field seasons in northern Norway, NMMF worked alongside the Norwegian Defence Research Establishment (FFI), LKARTS-Norway, Aarhus University, and North Carolina State University to close that gap, safely catching and releasing minke whales to record the first direct hearing measurements from a baleen whale. Its findings are now helping researchers and regulators understand how ocean noise affects some of the largest animals on Earth.
Why This Research Matters
Ocean noise is a growing, far-reaching problem for the animals that depend on sound to survive.
Sound behaves differently underwater than it does in air. It travels farther and faster, with far less energy lost along the way, which is exactly why whales rely on it to communicate, find food, and navigate across entire ocean basins. That same efficiency means human-made noise, sometimes called anthropogenic noise, travels just as well. A loud enough sound can be detected thousands of miles from its source.
Not all sound is noise. In general, noise refers to sound that is unwanted or disruptive, and by that measure, the ocean has been getting noisier for a long time. Over the past century, human activity has steadily added to the ocean’s soundscape. Mapping the seafloor, searching for oil and gas, commercial shipping, recreational boating, fisheries, and military sonar all contribute sound, and little of it stays local. Emerging technologies, like networks of underwater sensors sometimes called the “Underwater Internet of Things,” may add still more in the years ahead.
Ocean noise is a growing global concern.
In 2026, the OCEANOISE Scientific Advisory Committee called for coordinated action across science, policy, conservation, and industry to reduce underwater noise, a sign of how seriously the issue is now being taken worldwide.
Baleen whales depend on sound
In the ocean, hearing is part of how whales understand the world.
Baleen whales, the group that includes minke, blue, humpback, and gray whales, are named for the comb-like plates in their mouths that let them filter tiny prey from seawater. They also depend heavily on sound. It’s likely how they communicate across enormous distances, and potentially locate food and navigate while migrating.
Human-made noise can interfere with these functions. It may make it harder for a whale to communicate, forage, or hear an approaching ship in time to avoid it. Prolonged exposure to high noise levels may cause temporary or permanent hearing loss, and can potentially raise stress in ways that affect health and reproduction over time, a serious concern for species that are already endangered and reproduce slowly.
Why hearing matters for protection
Knowing what a whale can hear is the first step to protecting it.
Not every sound in the ocean affects a whale the same way. Ocean noise spans many frequencies, and a whale’s ability to hear varies across that range. Some sounds fall outside what it can perceive, others land squarely in the frequencies it hears best. Knowing the difference is what makes direct hearing measurements so valuable. They tell scientists exactly which kinds of noise are worth worrying about, and which aren’t.
Until this study, that data didn’t exist for any baleen whale. Scientists could only estimate hearing from ear anatomy and the sounds whales make, a gap serious enough that the Subcommittee on Ocean Science and Technology’s (SOST) Interagency Task Force on Ocean Noise and Marine Life named it a priority for whale protection. NMMF, FFI, and LKARTS-Norway took on the challenge, later joined by Aarhus University and North Carolina State University, and set out to record the first audiogram, or hearing sensitivity curve, ever produced for a baleen whale. The work was funded through the Task Force by the Office of Naval Research (ONR), Bureau of Ocean Energy Management (BOEM), National Oceanic and Atmospheric Administration (NOAA), U.S. Navy Living Marine Resources (LMR), and the Marine Mammal Commission (MMC).
Why Minke Whales
The smallest baleen whale made a first attempt possible.
Direct hearing tests are hard to perform in baleen whales, a group that includes the largest animals on Earth. Minke whales (Balaenoptera acutorostrata), the smallest baleen whale species, were the most realistic candidates for a first attempt. Their predictable migration north along the Norwegian coast each early summer also made a catch-and-release study possible.
How the Project Works
A careful catch-and-release process.
Over four field seasons ending in 2024, researchers worked in northern Norway each late spring and early summer, when minke whales migrate north toward Arctic waters. The team focused on adolescent whales, whose smaller size made handling safer and testing more likely to succeed. Animal welfare was built into every stage, from the timing of the fieldwork to veterinary evaluation, hearing testing, release, and follow-up monitoring.
Step 1
Following the migration
The project’s timing and location were built around the minke whales’ seasonal migration through a narrow stretch of the Norwegian coast.
Step 2
Guiding the whale into a natural basin
When a whale entered the area, researchers used guide nets to direct it into a natural basin between two small islands, then closed barrier nets behind it. The whale had plenty of room to swim and dive freely inside.
Step 3
Veterinary evaluation
Before testing began, two marine mammal veterinarians assessed the whale and confirmed it was healthy enough to proceed.
Step 4
Moving into the testing area
Once cleared, a net suspended between two boats guided the whale toward an opening in a nearby fish farm, a large circular net enclosure.
Step 5
Supporting the whale for hearing testing
Inside the enclosure, the opening was closed and the net lifted beneath the whale to form a hammock. This limited movement during testing while keeping its blowhole above water and its body submerged.
Step 6
Measuring the brain’s response to sound
Researchers tested hearing using the auditory evoked potential (AEP) method, which measures the small electrical signals the brain produces in response to sound. It’s the same principle behind newborn hearing screenings, and a method already used regularly to test hearing in dolphins, porpoises, and other toothed whales.
Step 7
Release and monitoring
After testing, each whale was released back into the fish farm and watched for two hours for any sign of distress before being guided back through the basin and out to sea to continue its migration. Every whale that completed testing was fitted with a satellite tag so researchers could track its movements for months afterward.
Animal Welfare and Safeguards
Every stage was designed to protect the whale first.
Every stage of the study, from which whales were selected to how stress was tracked during and after testing, was designed to protect the animals’ welfare and allow for a quick release if needed.
Smaller whales, lower risk
Handling any wild animal carries some risk. Choosing adolescent minke whales, and drawing on safety protocols developed for prior hearing studies with wild belugas and dolphins, helped keep that risk as low as possible. Specialist groups also helped shape the whale-handling procedures used in the field.
Veterinary oversight
Two marine mammal veterinarians evaluated each whale before testing and continued monitoring it throughout.
Stress is closely monitored
The team tracked both behavior and physiology throughout each procedure. They monitored respiration rate during capture and testing, ran periodic on-site blood tests for stress indicators, and tracked heart rate the entire time. If a veterinarian determined a whale was too stressed to continue, the team could release it within moments by lowering the fish farm net.
Follow up after release
Every whale that was tested left with a satellite tag, letting researchers follow its movements for weeks or months afterward and confirm it returned to normal behavior. Some tags kept transmitting long enough to track the whale well into its next migration south.
What the study found
Four whales, four field seasons, and one major surprise.
Minke whales tested
Field seasons, ending 2024
Ultrasonic hearing confirmed
The first whale researchers caught already had a story of its own. It arrived with a length of fishing net wound tightly around its upper jaw, with tissue grown in around the netting. It was clear evidence it had been entangled for some time. Before any hearing test began, the team removed the net. Without that intervention, the whale may not have survived. It’s a reminder that this work provided the opportunity to assist whales already affected by human activity.
Over four field seasons, the team safely tested the hearing of four minke whales, and all four returned to normal behavior soon after release. The first breakthrough came from the previously entangled whale: researchers recorded an auditory brainstem response (ABR), the foundational measurement in AEP testing that must be recorded before future tests can be made. This was the first ever ABR collected from a baleen whale.
With the second whale, researchers pushed further and tested the upper limit of its hearing range. The result surprised everyone involved. Minke whales can hear well into the ultrasonic range, above 45 kHz, higher than their ear anatomy or vocalizations had suggested. The finding, published in the journal Science in 2024, made headlines among marine scientists worldwide. 1
One hypothesis explains why the whale’s ultrasonic hearing exists. The frequencies minke whales hear best overlap closely with the echolocation clicks orcas use while hunting. Minke whales are orca prey, so the ability to detect that specific sound may be the product of a long evolutionary pressure: whales that could hear their predator coming were the ones that survived to pass on the trait.
Together, the results made two things clear. Direct measurement matters. The anatomical models researchers had relied on for years underestimated the whales’ upper hearing range, proof that estimates alone have limits. At the same time, the models weren’t far off, and with some adjustment, they can now be used with more confidence for other baleen whale species that can’t be tested directly.
- Houser DS, Kvadsheim PH, Kleivane L, Mulsow J, Ølberg RA, Harms CA, Teilmann J, Finneran JJ. 2024. Direct hearing measurements in a baleen whale suggest ultrasonic sensitivity. Science 386(6724):902–906. ↩︎
Read More
Read more about the project.
Scientific Snapshot
Understanding Whale Hearing to Protect Them from Ocean Noise
Want to dive deeper into the science? This closer look walks through the methods behind the hearing tests and what the data actually shows.
FAQ
Frequently Asked Questions
Answers to the questions we hear most often about animal welfare and how this research was done.
