Beluga whales are known for their vocal abilities, which they use to communicate with each other and navigate their environment.
But in Cook Inlet, Alaska, where a small and isolated population of belugas lives, their voices are being drowned out by commercial ship noise.
This could have serious consequences for their survival, as a new study reveals.
The Vocal Repertoire of Cook Inlet Belugas
OLIVIER MORIN/AFP via Getty Images
The Cook Inlet beluga whales are one of the most endangered marine mammal populations in the world, with only about 331 individuals left.
They face multiple threats, such as habitat loss, pollution, hunting, and climate change. But one of the most pressing issues is the increasing noise from human activities, especially shipping, which is the dominant source of underwater noise in the inlet.
Belugas rely on sound for many aspects of their life, such as finding food, avoiding predators, and maintaining social bonds.
They produce a variety of vocalizations, such as whistles, pulsed calls, and combined calls, which can convey different information and functions.
For example, whistles are often used for contact calls, pulsed calls for echolocation, and combined calls for complex communication.
To better understand how Cook Inlet belugas communicate and how ship noise affects them, a team of researchers from the University of Washington, the National Oceanic and Atmospheric Administration, and other institutions conducted a comprehensive analysis of their vocal behavior.
They recorded and measured over 1,600 beluga calls from 2016 to 2019, and classified them into 41 call types based on their acoustic features.
They also compared the call types with those of other beluga populations, and found that Cook Inlet belugas have a distinct and diverse vocal repertoire, which reflects their unique ecology and history.
The researchers also investigated how ship noise interferes with beluga communication, by measuring the signal-to-noise ratio (SNR) of the calls in the presence of different ship noise levels.
SNR is a measure of how much a signal stands out from the background noise, and a lower SNR means a higher risk of masking, which is the inability to detect a signal due to noise.
The results showed that all seven of the most common call types of Cook Inlet belugas were partially masked by distant ship noise and completely masked by close ship noise in the frequency range of 0-12 kHz, which is the main range of beluga hearing and vocalization.
This means that belugas may not be able to hear each other or their surroundings when ships are nearby, which could impair their communication, navigation, and survival.
The researchers also found that the masking effect was more severe for whistles than for pulsed calls, because whistles have a narrower frequency bandwidth and a lower sound pressure level than pulsed calls.
This suggests that contact calls may be more vulnerable to noise interference than echolocation calls, which could affect the social cohesion and coordination of beluga groups.
The Implications for Conservation
The study provides important insights into the vocal behavior and the noise exposure of Cook Inlet belugas, which can inform the management and conservation of this endangered population.
The researchers recommend that noise mitigation measures, such as reducing ship speed, rerouting ship traffic, and implementing quiet ship technology, should be implemented to protect the acoustic habitat and the communication of Cook Inlet beluga.
They also suggest that further research is needed to understand how belugas cope with noise, such as by changing their call frequency, duration, or rate, or by shifting their distribution or activity patterns3.
Additionally, they propose that long-term monitoring of beluga vocalizations and noise levels, as well as behavioral and physiological studies, are essential to assess the impacts of noise on the health and fitness of Cook Inlet belugas.
The study highlights the importance of sound for beluga whales, and the challenges they face in a noisy world.
By listening to their voices, we can learn more about their lives and needs, and help them survive and thrive in their natural habitat.
