Particle motion and pressure soundscape in outdoor vs indoor set-up

Underwater sound consists of particle motion and sound pressure. Due to technical difficulties only sound pressure is measured in most sound impact studies on fish and invertebrates. However, sound pressure alone may not adequately reflect the actual acoustic stimulus, especially in tanks, basins and near-field conditions. To test the acoustic validity of different experimental settings, we measured particle motion (in velocity) and sound pressure soundscapes of two set-ups for sound impact studies on fish: an outdoor floating pen and an indoor basin. During sound exposure, there was a gradient in particle velocity as well as in the outdoor floating pen and a standing wave in the basin. The ratio between particle velocity and sound pressure was consistent in the floating pen, but not in the basin. These findings confirm the concerns about the acoustic validity and variability between particle motion and sound pressure in basins (and tanks). Therefore, we encourage researchers to measure both particle motion and sound pressure to gain insight in the actual acoustic stimulus, in order to better interpret and understand its effect on fish and aquatic invertebrates.