Marine mammal hearing and acoustic trauma: basic mechanisms, marine adaptations, and beaked whale anomalies

TitleMarine mammal hearing and acoustic trauma: basic mechanisms, marine adaptations, and beaked whale anomalies
Publication TypeReport
Year of Publication1998
AuthorsKetten, D. R.
EditorsD' Amico, A., and W. C. Verboom
Series TitleReport of the Bioacoustics Panel, NATO/SACLANT
Date Published1998
TypeUnpublished Report
Call NumberDRK6793
Keywordsacoustic trauma, auditory pathology, beaked whales, blast trauma, explosive trauma, hearing, hearing loss, hearing pathology, marine mammals, morphology, odontocetes, trauma

Concomitant with increasing concern over the impact of anthropogenic sounds in the oceans, there has been a dramatic increase recently in the research efforts on marine mammal hearing. The resulting data suggest marine mammals ears are more diverse and complex than previously appreciated, with acoustic capabilities spanning infra to ultrasonic ranges. Whales in particular have strikingly different adaptations from those of land mammals, with specialized soft tissue sound conduction paths, 50% greater octave spans than most land mammals, and two to three-fold the auditory neural densities of any other mammal known. Recent data also show that despite physical adaptations that could diminish acoustic impacts, whales are not impervious to acoustic trauma and, like land mammals, their susceptibility to auditory damage varies among species. Beaked whales, because of their rarity and short surface intervals are amongst the least understood of all marine mammals, particularly in terms of hearing. Current anatomical data show that their ears are predominantly ultrasonic adapted and should therefore have relatively poor sensitivities to lower frequencies. However, these data also show that beaked whales have unusually well-developed vestibular structures which may anomalously enhance beaked whale sensitivities to intense, low frequency sounds.