Temporary hearing threshold shift in harbor seals (Phoca vitulina) due to one-sixth-octave noise bands centered at 0.5, 1, and 2 kHz

Abstract

This study concludes a larger project on the frequency-dependent susceptibility to noise-induced temporary hearing threshold shift (TTS) in harbor seals (Phoca vitulina). Here, two seals were exposed to one-sixth-octave noise bands (NBs) centered at 0.5, 1, and 2 kHz at several sound exposure levels (SELs, in dB re 1 μPa2s). TTSs were quantified at the center frequency of each NB, half an octave above, and one octave above, at the earliest within 1–4 min after exposure. Generally, elicited TTSs were low, and the highest TTS1–4 occurred at half an octave above the center frequency of the fatiguing sound: after exposure to the 0.5-kHz NB at 210 dB SEL, the TTS1–4 at 0.71 kHz was 2.3 dB; after exposure to the 1-kHz NB at 207 dB SEL, the TTS1–4 at 1.4 kHz was 6.1 dB; and after exposure to the 2-kHz NB at 215 dB SEL, TTS1–4 at 2.8 kHz was 7.9 dB. Hearing always recovered within 60 min, and susceptibility to TTS was similar in both seals. The results show that, for the studied frequency range, the lower the center frequency of the fatiguing sound, the higher the SEL required to cause the same TTS.

Temporary Hearing Threshold Shift in California Sea Lions (Zalophus californianus) Due to a Noise Band Centered at 32 kHz

“…The 6 dB onset of TTS12-16 (quantified after some recovery of hearing had occurred) in M02 after exposure to the NB at 32 kHz was not reached, but a 4.3 dB TTS occurred after exposure to an SEL of 192 dB re 1 µPa 2 s (at 32 kHz; Figure 3b). These results from the present study, combined with 6 dB TTS onset SELs after exposure to fatiguing sounds centered at 0.6, 1, 2, 4, 8, and 16 kHz (Kastelein et al, 2021b(Kastelein et al, , 2022a(Kastelein et al, , 2022b, suggest that susceptibility to TTS is frequencydependent in California sea lions (Figure 8), as it is in other marine mammals in which TTS has been tested: bottlenose dolphins (Tursiops truncatus; Finneran & Schlundt, 2013), harbor porpoises (Kastelein et al, 2021a), Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis; Popov et al, 2011), and harbor seals (Kastelein et al, 2020b).…”

“…Both within and between species, there is variation in the causes and effects of TTS and in recovery times. Fatiguing sounds of different amplitudes and durations result in varying levels of reduced hearing sensitivity at different frequencies, and recovery times also vary (Popov et al, 2014;Finneran, 2015;Kastelein et al, 2020aKastelein et al, , 2020bKastelein et al, , 2021aKastelein et al, , 2021b. The present study is one of five in a comprehensive research project on TTS in California sea lions.…”