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. 2010 Nov 3;5(11):e13824.
doi: 10.1371/journal.pone.0013824.

Hearing loss in stranded odontocete dolphins and whales

David Mann  1 , Mandy Hill-Cook, Charles Manire, Danielle Greenhow, Eric Montie, Jessica Powell, Randall Wells, Gordon Bauer, Petra Cunningham-Smith, Robert Lingenfelser, Robert DiGiovanni Jr, Abigale Stone, Micah Brodsky, Robert Stevens, George Kieffer, Paul Hoetjes
Affiliations

Hearing loss in stranded odontocete dolphins and whales

David Mann et al. PLoS One. .

Abstract

The causes of dolphin and whale stranding can often be difficult to determine. Because toothed whales rely on echolocation for orientation and feeding, hearing deficits could lead to stranding. We report on the results of auditory evoked potential measurements from eight species of odontocete cetaceans that were found stranded or severely entangled in fishing gear during the period 2004 through 2009. Approximately 57% of the bottlenose dolphins and 36% of the rough-toothed dolphins had significant hearing deficits with a reduction in sensitivity equivalent to severe (70-90 dB) or profound (>90 dB) hearing loss in humans. The only stranded short-finned pilot whale examined had profound hearing loss. No impairments were detected in seven Risso's dolphins from three different stranding events, two pygmy killer whales, one Atlantic spotted dolphin, one spinner dolphin, or a juvenile Gervais' beaked whale. Hearing impairment could play a significant role in some cetacean stranding events, and the hearing of all cetaceans in rehabilitation should be tested.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Audiogram of MML0807 (Ginger; filled triangles), a juvenile bottlenose dolphin with normal hearing, and MML FB303 (Castaway; open squares), an adult bottlenose dolphin with hearing loss.
For Castaway, no response was detected at any frequency indicating that there was at least 40–100 dB hearing loss across all frequencies tested, and no response could be detected in response to click trains at 164 dBpeak re 1 µPa.
Figure 2
Figure 2. Results of hearing tests on two stranded rough-toothed dolphins.
A. Audiogram of R375 (filled triangles), a normal hearing rough-toothed dolphin, and highest level tested for Dancer (open squares) rough-toothed (open squares) for which no response was detected at any frequency). For Dancer, there was at least a 70 dB hearing loss across all frequencies tested. B. Click-train (600 Hz click rate) evoked potential traces from the hearing-impaired rough-toothed dolphin (Dancer) at four stimulus levels. The click train sound starts at 15 ms. The lowest level detected was about 154 dBpeak re 1 µPa.
Figure 3
Figure 3. Image of sponges removed from the stomach of Vixen, a stranded rough-toothed dolphin with profound hearing loss.
See this image and copyright information in PMC

References

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