Identifying Cetacean Hearing Impairment at Stranding Sites

Abstract: While noise is now considered a marine hazard that can directly affect cetaceans and induce a stranding, no clinical approach has yet introduced the detection of a possible hearing loss at a stranding site as a necessary practice. This can be explained by the lack of time when facing vital decisions for the animal’s welfare as well as the unavailability of reliable, lightweight, autonomous, and portable audiometry equipment. Herein, we correlate measured electrophysiological evidence of a permanent threshold shift (PTS) in a rehabilitated striped dolphin (Stenella coeruleoalba) that prevented its release, with the postmortem analysis of an abnormal dilatation of the central nervous system ventricles that prevented the correct acoustic reception of the animal. We further propose to follow a five-minute auditory evoked potential (AEP) standard protocol of hearing measurements in-air on cetaceans at a stranding site that includes the stimulation of auditory brainstem responses (ABRs) with a single 4-μs broadband (> 150 kHz) pulse at three decreasing levels (129, 117, and 105 dBpp re 1 μPa at 15 cm), which covers most of the cetaceans’ known maximum acoustic sensitivity and allows the immediate sensing of an individual’s hearing capability before any final clinical decision is taken.

Key Words: auditory evoked potentials, cetaceans, stranding, hearing impairment, striped dolphin, Stenella coeruleoalba, permanent threshold shift 

Document Type: research article

DOI: 10.1578/AM.33.1.2007.100

Page Numbers: 100 – 109

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