# Naval sonar induces an anaerobic swimming gait in beaked whales

## TL;DR

Naval sonar causes beaked whales to use an oxygen-saving swimming gait, which may lead to strandings.

## Contribution

The study identifies a specific swimming gait used by beaked whales in response to sonar exposure, suggesting a physiological mechanism for strandings.

## Key findings

- B-strokes are used during descent and ascent in sonar-exposed dives, unlike baseline conditions.
- B-stroke onset occurs when sonar levels exceed 100 dB for more than three minutes.
- Sonar exposure leads to earlier use of B-strokes, indicating an oxygen-saving strategy.

## Abstract

Naval sonar can disrupt beaked whale diving behaviour, in some cases leading to lethal strandings. Diving disruption likely involves a physiological response, which remains poorly understood. Beaked whales may exceed their aerobic dive limit during long-duration deep-foraging dives and later in those dives, during ascent, initiate a unique strong gait (B-strokes), hypothesized to recruit anaerobic fast-twitch fibres. We compared the use of B-strokes during exposed and unexposed dives in four species of beaked whales. Contrasting the highly context-specific use of B-strokes during ascents from deep-dives in baseline conditions, during sonar exposure, B-strokes were used during descent and ascent phases of both deep and shallow dives. B-stroke onset occurred during all sonar exposure periods with levels above 100 dB re 1 µPa that lasted more than three minutes. The use of B-strokes during descent indicates these animals start using an oxygen-saving strategy earlier in exposed (16 ± 13 min) vs. unexposed dives (33 ± 14 min). This change in swimming gait when exposed to an external threat likely evolved to enable flexible escape responses from predators. However, if prolonged, such responses could lead to physiological changes that contribute to gas bubble formation and growth that could lead to animals stranding.

The online version contains supplementary material available at 10.1038/s41598-025-22490-5.