Credit: T. A. MOONEY

Biol. Lett. doi:10.1098/rsbl.2009.0099 (2009)

Mid-frequency sonar — such as that deployed on military ships — can induce temporary hearing loss in Atlantic bottlenose dolphins (Tursiops truncatus), which some people fear can cause them to lose their way and end up stranded on beaches.

Aran Mooney and his colleagues at the University of Hawaii in Kaneohe exposed a trained, captive dolphin to intensive sonar pings to a level of 214 decibels, which induced hearing loss and behavioural changes. Hearing function was measured using an electrode placed atop the head (pictured) to detect auditory evoked potentials in the brainstem. Tests showed that repeated exposures are required to produce the hearing loss.