Marine biologists from Norway, the United States, and Denmark recently achieved a significant milestone by conducting the first hearing test on a live baleen whale. This groundbreaking study, published in the journal Science, involved capturing and recording the brain waves of two wild minke whales as they listened to a series of sounds. This research is a crucial step in understanding how human-generated noise pollution in the oceans might impact marine life, especially large marine mammals like whales.
In recent decades, concerns about the increasing levels of human-produced noise in the oceans have intensified. Commercial shipping, military sonar, underwater drilling, and seismic exploration all contribute to the noise pollution that can disrupt the behavior and well-being of marine species. The primary motivation behind this study was to gather concrete data on the hearing capabilities of baleen whales, allowing scientists to evaluate the potential impact of ocean noise more accurately.
The research team chose minke whales for the study due to their smaller size compared to other baleen whales, making them more manageable subjects. Minke whales, which can grow up to 10 meters long, are the smallest members of the baleen whale family, which also includes much larger species like blue and humpback whales. Understanding how they perceive sound could provide insights applicable to other baleen whales as well.
The first step of the study was to select a suitable location for capturing and studying the whales. The team chose a narrow channel between two islands off the coast of Norway, a natural migratory route for minke whales. This channel offered an ideal setting to observe and work with the whales because of its relatively confined and controlled environment. The researchers placed netted barriers at strategic points to guide the whales toward a smaller enclosure without causing them distress.
Once two minke whales entered the designated area, the researchers used a net to gently raise them to the surface. This allowed them to attach electrodes to the animals’ heads while minimizing stress and avoiding invasive techniques. The electrodes were used to monitor and record brain wave activity as the whales were exposed to various sounds through underwater speakers positioned nearby.
The team played a range of recorded sounds at different frequencies, focusing on both low-frequency noises, which are thought to be most relevant to whale communication, and high-frequency ultrasonic sounds. The testing phase lasted for 30 minutes for one whale and 90 minutes for the other. Throughout this period, the electrodes captured real-time data on the whales’ neural responses to the auditory stimuli. After testing, the researchers released the whales back into the open sea.
The results of this hearing test were both anticipated and surprising. As expected, the whales demonstrated the ability to detect many sounds that had been inferred from studies on the ear structures of deceased whales. This confirmed some earlier hypotheses about how baleen whales hear and process sound. However, the researchers made a surprising discovery: the minke whales also responded to ultrasonic frequencies—sounds that are higher than those previously assumed to be detectable by baleen whales.
The detection of ultrasonic sounds by the minke whales opens up new areas of inquiry in marine science. Traditionally, baleen whales were thought to be limited to lower frequency ranges, given the anatomical structure of their hearing organs. This new finding suggests that these whales may have a broader auditory range than previously believed, potentially giving them an advantage in detecting predators like killer whales, which communicate using high-frequency clicks. This insight could reshape our understanding of how baleen whales perceive their environment and avoid threats in the ocean.
The implications of this study extend beyond the basic biology of baleen whales. If all baleen whales can indeed hear ultrasonic sounds, it will require a re-evaluation of earlier research on how these animals react to various underwater noises. Sonar, underwater echo sounders, and other man-made noises produced by ships may have a broader impact on whale behavior than previously thought. This new understanding could lead to changes in how maritime activities are conducted, particularly in areas known to be frequented by whales.
The findings also highlight the importance of minimizing noise pollution in the oceans. Increased awareness of the auditory sensitivity of baleen whales could drive stricter regulations on sonar use, noise limits for ships, and protected zones for marine wildlife. For example, the ability to hear high-frequency sounds could mean that whales are more disturbed by certain types of sonar than earlier studies indicated. The military and commercial sectors might need to adjust their technology to mitigate its impact on marine life.
Moreover, this study sets a precedent for the methodology used in future research on marine animals. Conducting non-invasive hearing tests in the wild represents a significant technical achievement, offering a model for how scientists can gather crucial behavioral and physiological data without harming the subjects. The success of the minke whale study demonstrates that it is possible to perform detailed sensory research on large marine mammals in their natural habitat, avoiding the ethical and practical challenges associated with captivity.