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.
↵* These authors contributed equally to this work
T.A.M. led the data collection with the assistance of all other authors and those in the acknowledgements. T.A.M. and M.C. led the analyses and writing with support and editing from all other authors (C.G., L.Q. and E.G.) including R.H. contributing some figures. T.A.M. and M.C. acquired the audiogram project support with overall project support acquired by the other authors (C.G., L.Q. and E.G.).
The authors declare no competing financial interests.
Project funding and field support were provided by Georgia Aquarium and the National Marine Mammal Laboratory of the Alaska Fisheries Science Center (NMML/AFSC). Field work was also supported by National Marine Fisheries Service Alaska Regional Office (NMFS AKR), Woods Hole Oceanographic Institution (WHOI) Arctic Research Initiative, WHOI Ocean Life Institute, US Fish and Wildlife Service, Bristol Bay Native Association, Alaska SeaLife Center, Shedd Aquarium and Mystic Aquarium. We greatly appreciate the support from all their directors. Audiogram analyses were funded by the Office of Naval Research award number N000141210203 (from Michael Weise).
- © 2014. Published by The Company of Biologists Ltd