Sonar-Induced Temporary Hearing Loss in Dolphins

A new study published in the August 23, 2009 edition of the journal Biology Letters (Biol. Lett., Vol. 5 no. 4, pp. 565-567; doi: 10.1098/rsbl.2009.0099) examines temporary hearing loss in dolphins caused by sonar. A copy of the abstract is provided here. For a copy of the full study or a subscription to the journal, please visit: rsbl.royalsocietypublishing.org/

Title: Sonar-induced temporary hearing loss in dolphins

Authors: T. Aran Mooney , Paul E. Nachtigall, Stephanie Vlachos

Author Affiliations: Department of Zoology, HIMB, University of Hawaii, Kaneohe, HI 96734 USA

Abstract: There is increasing concern that human-produced ocean noise is adversely affecting marine mammals, as several recent cetacean mass strandings may have been caused by animals' interactions with naval 'mid-frequency' sonar. However, it has yet to be empirically demonstrated how sonar could induce these strandings or cause physiological effects. In controlled experimental studies, we show that mid-frequency sonar can induce temporary hearing loss in a bottlenose dolphin (Tursiops truncatus). Mild-behavioural alterations were also associated with the exposures. The auditory effects were induced only by repeated exposures to intense sonar pings with total sound exposure levels of 214â ...dB re: 1â ...μPa2â ...s. Data support an increasing energy model to predict temporary noise-induced hearing loss and indicate that odontocete noise exposure effects bear trends similar to terrestrial mammals. Thus, sonar can induce physiological and behavioural effects in at least one species of odontocete;however, exposures must be of prolonged, high sound exposures levels to generate these effects.