Binaural AEP audiograms in seven Beluga whales (Delphinapterus leucas) from the Okhotsk Sea population

Abstract

Hearing thresholds were measured and audiograms were obtained in seven belugas, three males and four females, provisionally 2 to 7 years old. The measurements were performed using a transducer located 1 m in front of the head. The stimuli were tone pip trains of carrier frequencies ranging from 11.2 to 128 kHz with a pip rate of 1 kHz. Auditory evoked potentials (the rate following responses) were recorded from the head vertex. In majority of the subjects, audiograms were similar to the typical odontocete audiograms with the lowest thresholds (from 53.7 to 56.4 dB re 1 μPa) at mid-frequency range (from 32 to 64 kHz) and a sharp thresholds rise (up to 79.5 dB re 1 μPa) at high frequencies (90–128 kHz). One beluga (female, 6–7 years old) featured an asymmetric hearing loss within a frequency range from 22.5 to 54 kHz. The reason for the loss is the subject for not defined. The evoked potential audiograms should be included into base screening of odontocete subjects involved in any kind of hearing research. Work supported by the Russian Science Foundation (project # 17-74-20107), the Russian Foundation for Basic Research and The Russian Geographic Society.]