01790nas a2200133   4500008004100000245012300041210006900164520129100233100002301524700002301547700001801570700001701588856005101605       2019                        eng d00aLong-term evidence of noise-induced permanent threshold shift in a harbor seal ( <i>Phoca vitulina</i>               )0 aLongterm evidence of noiseinduced permanent threshold shift in a3 a<p>In psychophysical studies of noise-induced hearing loss with marine mammals, exposure conditions are often titrated from levels of no effect to those that induce significant but recoverable loss of auditory sensitivity [temporary threshold shift (TTS)]. To examine TTS from mid-frequency noise, a harbor seal was exposed to a 4.1-kHz underwater tone that was incrementally increased in sound pressure level (SPL) and duration. The seal&#39;s hearing was evaluated at the exposure frequency and one-half octave higher (5.8&thinsp;kHz) to identify the noise parameters associated with TTS onset. No reliable TTS was measured with increasing sound exposure level until the second exposure to a 60-s fatiguing tone of 181&thinsp;dB re 1 &mu;Pa SPL (sound exposure level 199&thinsp;dB re 1 &mu;Pa2s), after which an unexpectedly large threshold shift (&gt;47&thinsp;dB) was observed. While hearing at 4.1&thinsp;kHz recovered within 48&thinsp;h, there was a permanent threshold shift of at least 8&thinsp;dB at 5.8&thinsp;kHz. This hearing loss was evident for more than ten years. Furthermore, a residual threshold shift of 11&thinsp;dB was detected one octave above the tonal exposure, at 8.2&thinsp;kHz. This hearing loss persisted for more than two years prior to full recovery.</p>
1 aReichmuth, Colleen1 aSills, Jillian, M.1 aMulsow, Jason1 aGhoul, Asila  uhttp://asa.scitation.org/doi/10.1121/1.5129379