abstract

A number of cetaceans of several different species have been found to have severe hearing impairment following a period of rehabilitation, including two stranded rough-toothed dolphin calves. Because of concern that the deafness might be caused by drugs used during the medical treatment of the animals, a study was designed to test the hearing of stranded dolphins upon admission to rehabilitation prior to the administration of any ototoxic drugs and test them again at the end of rehabilitation. Auditory evoked potentials were used to measure hearing of three stranded Risso's dolphins prior to and after treatment with Amikacin as well as a number of other drugs reported to be potentially ototoxic. Hearing was measured using sounds presented through a jawphone at 40, 80, and 120 kHz, while the dolphins were held at the water surface as part of the regular veterinary examination. None of the animals tested have shown any significant decrease in auditory sensitivity after measurements of up to five months from stranding. Although more species and drugs need to be tested, it is likely that the earlier animals that had tested as being severely hearing-impaired had arrived in rehabilitation that way, and it is possible that some dolphin strandings may be caused by hearing loss.