Amphibious seals are less susceptible to hearing loss from airborne noises than their relatives and some can learn to close their ears for protection.
Seals are exposed to a variety of human noises in coastal environments, from underwater noises due to shipping, dredging, and sonars, to airborne noises like cars and planes. It is important to study the impact of these sounds on the animals’ hearing.
Reichmuth et al. analyzed a historical dataset from the University of California Santa Cruz to determine the onset of temporary threshold shift (TTS) in seals, which is the temporary decrease in hearing from loud noises.
“Our team worked together over several years to complete and publish this study, the results of which are still very relevant today,” said author Colleen Reichmuth.
To perform the experiments, the team trained a northern elephant seal and a harbor seal to voluntarily leave their pools and enter a hearing chamber to perform listening experiments. They first determined the hearing sensitivity of the two seals in a controlled, quiet environment, and then after exposure to noise of fixed bandwidth, level, and duration, they retested the seals so the researchers could measure any hearing changes.
They found that compared to related species — sea lions and fur seals — seals appear to be less susceptible to hearing loss from airborne noise. By providing missing data for amphibious seals, “these results can be used to refine noise exposure criteria for marine mammals,” Reichmuth said.
They also found that the duration of the noise was more impactful to changes in TTS than noise level.
Surprisingly, the team observed that one harbor seal experienced a change in noise sensitivity over the course of the experiment, as it learned to close its ears to protect itself from the noise, “an intriguing possibility that merits further study,” Reichmuth said.
Source: “Temporary threshold shifts from mid-frequency airborne noise exposures in seals,” by Colleen Reichmuth, Jillian M. Sills, Jason Mulsow, Marla M. Holt, and Brandon L. Southall, Journal of the Acoustical Society of America (2025). The article can be accessed at https://doi.org/10.1121/10.0036849 .