Research harbour seals and pile driving sound

^{Kastelein, R.A., de Jong, C., Helder-Hoek, L. Defillet, L., Terhune, J.M., Kuiphof, F., and Van Acoleyen, L. (2025) Effect of impact pile-driving playback sound on harbor seal (Phoca vitulina) behavior: dose-response relationship and frequency weighting. Aquatic Mammals 51(4), 319-335, DOI. Bron.}

Two experiments were conducted to investigate how seals respond to loud underwater sounds, such as those generated during the pile driving of foundation piles for offshore wind turbines.

Two female seals in a quiet pool were exposed to playback recordings of pile driving (46 hammer blows per minute) at seven different sound levels ranging from 125 to 161 dB. The seals began to show noticeable changes in behavior at 131 dB and 137 dB, and responded clearly from 143 dB onwards.

This experiment examined whether it is meaningful to adjust sound levels based on how seals perceive sound. They were exposed to three versions of the same pile-driving noise: full, low-frequency filtered, and high-frequency filtered, all at the same unweighted sound level. Both seals responded to all three sounds, but especially to the full and high-frequency versions. This indicates that it is primarily the high frequencies of the pile driving that trigger the behavioral responses.

Seals respond to loud pile-driving sounds, especially the high frequencies. To protect their behavior, it is important that noise mitigation measures focus on reducing the high-frequency components of the pile-driving noise. For predicting their behavior, it is better to take into account how seals perceive sound (weighted sound level) rather than just the raw noise.