Improved Techniques of Evoked-Potential Audiometry in Odontocetes

While hearing is the primary sensory modality for odontocetes, there are few data addressing variation within a natural population. This work describes the hearing ranges (4-150 kHz) and sensitivities of seven apparently healthy, wild beluga whales (Delphinapterus leucas) during a population health assessment project that captured and released belugas in Bristol Bay, Alaska. The baseline hearing abilities and subsequent variations were addressed. Hearing was measured using auditory evoked potentials (AEPs). All audiograms showed a typical cetacean U-shape; substantial variation (>30 dB) was found between most and least sensitive thresholds. All animals heard well, up to at least 128 kHz. Two heard up to 150 kHz. Lowest auditory thresholds (35-45 dB) were identified in the range 45-80 kHz. Greatest differences in hearing abilities occurred at both the high end of the auditory range and at frequencies of maximum sensitivity. In general, wild beluga hearing was quite sensitive. Hearing abilities were similar to those of belugas measured in zoological settings, reinforcing the comparative importance of both settings. The relative degree of variability across the wild belugas suggests that audiograms from multiple individuals are needed to properly describe the maximum sensitivity and population variance for odontocetes. Hearing measures were easily incorporated into field-based settings. This detailed examination of hearing abilities in wild Bristol Bay belugas provides a basis for a better understanding of the potential impact of anthropogenic noise on a noise-sensitive species. Such information may help design noise-limiting mitigation measures that could be applied to areas heavily influenced and inhabited by endangered belugas.

Section: Stimulus Presentationmentioning

confidence: 99%

Baseline hearing abilities and variability in wild beluga whales (Delphinapterus leucas)

Castellote

Mooney

Quakenbush

et al. 2014

“…1B) was 0.25 octave wide at a level of 0.5 of the power peak (-3 dB); its equivalent rectangular bandwidth was 0.32 octave. This type of test stimulus was used because it more effectively produced an EFR than a narrow-band sinusoidally modulated tone (Supin and Popov, 2007). The stimulus bandwidth was sufficiently narrow to assign a resulting measurement to the particular sound frequency with a tolerance of 0.25 octave.…”

Section: Test and Fatiguing Soundsmentioning

confidence: 99%

The limits of applicability of the sound exposure level (SEL) metric to temporal threshold shifts (TTS) in beluga whales, Delphinapterus leucas

Попов

Supin

Рожнов

et al. 2014

Self Cite

The influence of fatiguing sound level and duration on post-exposure temporary threshold shift (TTS) was investigated in two beluga whales (Delphinapterus leucas). The fatiguing sound was half-octave noise with a center frequency of 22.5 kHz. TTS was measured at a test frequency of 32 kHz. Thresholds were measured by recording rhythmic evoked potentials (the envelope following response) to a test series of short (eight cycles) tone pips with a pip rate of 1000 s −1 . TTS increased approximately proportionally to the dB measure of both sound pressure (sound pressure level, SPL) and duration of the fatiguing noise, as a product of these two variables. In particular, when the noise parameters varied in a manner that maintained the product of squared sound pressure and time (sound exposure level, SEL, which is equivalent to the overall noise energy) at a constant level, TTS was not constant. Keeping SEL constant, the highest TTS appeared at an intermediate ratio of SPL to sound duration and decreased at both higher and lower ratios. Multiplication (SPL multiplied by log duration) better described the experimental data than an equal-energy (equal SEL) model. The use of SEL as a sole universal metric may result in an implausible assessment of the impact of a fatiguing sound on hearing thresholds in odontocetes, including under-evaluation of potential risks.

“…The frequency spectra of such pips ( Fig.1B) were 0.25octaves wide at a level of 0.5 of the power peak (-3dB); their equivalent rectangular bandwidth was 0.32octaves. This sort of test stimulus was used because it more effectively produced the rhythmic auditory evoked response [the envelope following response (EFR)] than a narrow-band sinusoidally modulated tone (Supin and Popov, 2007). The stimulus bandwidth was sufficiently narrow to assign a resulting measurement to a particular sound frequency with a tolerance of ~0.25octaves.…”

Section: Test and Fatiguing Soundsmentioning

confidence: 99%

“…function was approximated by a straight regression line, which was extrapolated to the zero-response amplitude; the resulting test-sound level was considered to be the baseline threshold estimate (Supin and Popov, 2007).…”

Section: Evoked-potential Recording and Threshold Determinationmentioning

confidence: 99%

Hearing threshold shifts and recovery after noise exposure in beluga whales, Delphinapterus leucas

Supin

Рожнов

et al. 2013

Self Cite

SUMMARYTemporary threshold shift (TTS) after loud noise exposure was investigated in a male and a female beluga whale (Delphinapterus leucas). The thresholds were evaluated using the evoked-potential technique, which allowed for threshold tracing with a resolution of ~1min. The fatiguing noise had a 0.5octave bandwidth, with center frequencies ranging from 11.2 to 90kHz, a level of 165dBre.1μPa and exposure durations from 1 to 30min. The effects of the noise were tested at probe frequencies ranging from -0.5 to +1.5octaves relative to the noise center frequency. The effect was estimated in terms of both immediate (1.5min) postexposure TTS and recovery duration. The highest TTS with the longest recovery duration was produced by noises of lower frequencies (11.2 and 22.5kHz) and appeared at a test frequency of +0.5octave. At higher noise frequencies (45 and 90kHz), the TTS decreased. The TTS effect gradually increased with prolonged exposures ranging from 1 to 30min. There was a considerable TTS difference between the two subjects.