Dorian S. Houser et al., Direct hearing measurements in a baleen whale suggest ultrasonic sensitivity. Science 386, 902-906 (2024). DOI: 10.1126/science.ado7580
The science of sound
Studying animal communication is no easy feat, and underwater, the challenges grow exponentially. In the ocean, where vision fades quickly and scents drift unpredictably with the currents, sound takes center stage as the primary mode of communication.
In the air, low-frequency sounds travel a few kilometers at best, but underwater, the same sounds can travel tens to hundreds of kilometers. This makes sound an indispensable tool for marine animals to explore their environment and stay connected.
However, this reliance on sound has sparked concern over human-made noise pollution in the oceans. Since the early 2000s, research into the effects of naval sonar and industrial noise gained traction after a series of whale strandings were linked to acoustic disturbances. This has led scientists to study the hearing thresholds of various marine species to better understand how noise impacts ocean life.
Putting the ‘ear’ in ‘hear’
To measure an animal’s ability to hear, scientists often turn to the ear—examining how it responds to sound stimuli. Understanding an animal’s hearing range enables the creation of policies to minimize human noise in sensitive areas.
Audiograms, graphical representations of frequency-specific hearing sensitivity, have been developed for many marine species—but baleen whales remain an exception. Due to their immense size, they’ve been nearly impossible to test in the wild, leaving researchers to rely on behavioral studies and estimates, which often lack precision.
A promising tool for direct measurement is the auditory evoked potential (AEP) test. This method detects electrical signals in the brain triggered by sound stimuli. While AEP tests have been successfully conducted on smaller marine species, attempts on baleen whales, such as a stranded gray whale calf, have been limited and largely unsuccessful—until now.
How to catch a whale…and perform a hearing test
In 2023, researchers from the US and Norway achieved a breakthrough: they developed a catch-and-release system to briefly study minke whales in their natural environment. The tests took place in Vestfjorden, Norway, during the whales’ migration.
Using weighted purse seine nets, they safely captured two adolescent minke whales, affectionately named Ba23_2606a and Ba23_2706c. The whales were held for 90 and 30 minutes, respectively, and tested for their hearing range using AEP technology. Gold-plated suction cups placed on the whales’ skin recorded brain responses to sound, while an underwater transducer delivered auditory stimuli—chirps ranging from low to high frequencies.
Importantly, the process was non-invasive, and the whales were released with satellite tags to monitor their behavior post-capture. No adverse effects were observed.
Are you deaf? The orcas are coming!
The tests revealed something unexpected: minke whales are sensitive to frequencies between 45 and 90 kHz, significantly higher than the <45 kHz range previously assumed. This ability to detect high frequencies likely helps them evade predators like orcas, whose echolocation clicks fall in the 35–50 kHz range.
These findings challenge earlier assumptions about baleen whale hearing and suggest that conservation policies may need revision to reflect their broader auditory capabilities.
A promising future for whale hearing
This study marks the first use of electrophysiological methods to measure hearing in baleen whales—a non-invasive approach with immense potential for refinement. For instance, testing calves could yield more reliable data, as smaller body sizes reduce signal attenuation and eliminate age-related hearing loss from the equation.
Species like humpback and gray whales, which are more prone to stranding, present additional opportunities for AEP testing, provided the animals are treated ethically.
As human activity continues to amplify ocean noise, understanding and mitigating its impact on marine life is vital. Studies like this pave the way for informed conservation strategies, ensuring that we can coexist peacefully with the gentle giants of the sea.
Cover photo from Houser et al. mod.
I’m a former oceanographer with an MSc in Biological Oceanography from UConn where I studied mixotrophy in marine ciliates. After a year in Poland (studying freshwater critters) I moved to California. I currently work as a lab technician at Stanford. Outside of science, I enjoy a good book, a long run, and frozen fruit.