Effect of pile-driving sounds on harbor seal (Phoca vitulina) hearing

Abstract

Seals exposed to intense sounds may suffer hearing loss. After exposure to playbacks of broadband pile-driving sounds, the temporary hearing threshold shift (TTS) of two harbor seals was quantified at 4 and 8 kHz (frequencies of the highest TTS) with a psychoacoustic technique. The pile-driving sounds had: a 127 ms pulse duration, 2760 strikes per h, a 1.3 s inter-pulse interval, a ∼9.5% duty cycle, and an average received single-strike unweighted sound exposure level (SEL) of 151 dB re 1 μPas. Exposure durations were 180 and 360 min [cumulative sound exposure level (SEL): 190 and 193 dB re 1 μPas]. Control sessions were conducted under low ambient noise. TTS only occurred after 360 min exposures (mean TTS: seal 02, 1-4 min after sound stopped: 3.9 dB at 4 kHz and 2.4 dB at 8 kHz; seal 01, 12-16 min after sound stopped: 2.8 dB at 4 kHz and 2.6 dB at 8 kHz). Hearing recovered within 60 min post-exposure. The TTSs were small, due to the small amount of sound energy to which the seals were exposed. Biological TTS onset SEL for the pile-driving sounds used in this study is around 192 dB re 1 μPas (for mean received SEL of 151 dB re 1 μPa and a duty cycle of ∼9.5%).

Frequency of greatest temporary hearing threshold shift in harbor seals (Phoca vitulina) depends on fatiguing sound level

“…In addition, the percentage of time swimming at the water surface increased at the two highest SPLs (Table I). A similar phenomenon was seen in the same seals in response to pile driving sounds (Kastelein et al, 2018b). The animals in the present study may have spent time with their heads at the water surface in an attempt to reduce the received level.…”

“…Seal F01 showed a much stronger initial recovery (0.3 dB/min) than seal F02. All TTSs up to 6 dB recovered within 2 h, most within 1 h. In seal F02, TTS of around 19 dB recovered within 24 h. The results of the present study and studies by Kastelein et al (2012) and Kastelein et al (2018b) suggest that in harbor seals, similar TTSs, caused by different fatiguing sounds (one octave continuous noise band, intermittent impulsive sounds, and a CW) with different exposure levels and exposure times, require similar recovery times.…”

“…The seals received most of their daily fish ration during hearing test sessions. They were healthy throughout the study, and had participated in eight previous hearing studies, which had shown that they had sensitive and very similar hearing (Kastelein et al, 2009a;Kastelein et al, 2009b;Kastelein et al, 2010a;Kastelein et al, 2012;Kastelein et al, 2013b;Kastelein et al, 2015b;Kastelein et al, 2018a;Kastelein et al, 2018b). Variation in the animals' performance was minimized by making weekly adjustments (usually in the order of 100 g) to their daily food ration, based on their weight and performance during the previous week and the expected change in water and air temperatures in the following week.…”

“…After exposing two harbor seals to octave-band noise centered at 4 kHz, Kastelein et al (2012) tested their hearing only at 4 kHz. After exposing two harbor seals to playbacks of pile-driving sound (the one third octave band centered at 630 Hz contained the most energy), Kastelein et al (2018b) tested their hearing at 0.25, 0.5, 1, 2, 4, 8, 16, and 32 kHz, and only found TTS at 4 and 8 kHz (the highest TTS occurred at 4 kHz).…”

Estimating the effects of pile driving sounds on seals: Pitfalls and possibilities

“…A limited number of studies have investigated the effects of pile driving sounds on harbour seal hearing and behaviour. Recent playbacks of broadband piling sounds [$500-800 Hz, single-strike sound exposure level (SELss) of 152 dB re 1 lPa 2 Ás at 1 m depth, 2 m from the source] were found to cause onset of TTS at unweighted SELcums of around 192 dB re 1 lPa 2 Ás in two harbour seals in captivity (Kastelein et al, 2018). Small TTSs (2-4 dB) occurred in that experiment and hearing recovered within 60 min.…”