Effects of exposure to intermittent and continuous 6–7 kHz sonar sweeps on harbor porpoise (Phocoena phocoena) hearing

Abstract

Safety criteria for mid-frequency naval sonar sounds are needed to protect harbor porpoise hearing. A porpoise was exposed to sequences of one-second 6-7 kHz sonar down-sweeps, with 10-200 sweeps in a sequence, at an average received sound pressure level (SPLav.re.) of 166 dB re 1 μPa, with duty cycles of 10% (intermittent sounds) and 100% (continuous). Behavioral hearing thresholds at 9.2 kHz were determined before and after exposure to the fatiguing noise, to quantify temporary hearing threshold shifts (TTS1-4 min) and recovery. Significant TTS1-4 min occurred after 10-25 sweeps when the duty cycle was 10% (cumulative sound exposure level, SELcum: ∼178 dB re 1 μPa(2)s). For the same SELcum, the TTS1-4 min was greater for exposures with 100% duty cycle. The difference in TTS between the two duty cycle exposures increased as the number of sweeps in the exposure sequences increased. Therefore, to predict TTS and permanent threshold shift, not only SELcum needs to be known, but also the duty cycle or equivalent sound pressure level (Leq). It appears that the injury criterion for non-pulses proposed by Southall, Bowles, Ellison, Finneran, Gentry, Greene, Kastak, Ketten, Miller, Nachtigall, Richardson, Thomas, and Tyack [(2007). Aquat. Mamm. 33, 411-521] for cetaceans echolocating at high frequency (SEL 215 dB re 1 μPa(2)s) is too high for the harbor porpoise.

Assessing the Impact of Underwater Clearance of Unexploded Ordnance on Harbour Porpoises (Phocoena phocoena) in the Southern North Sea

“…Different TTS onset SEL thresholds have been measured in harbour porpoises for a variety of pulse types (Lucke et al, 2009;Kastelein et al, 2012bKastelein et al, , 2014bKastelein et al, , 2015aKastelein et al, , 2015b. Lucke et al (2009) determined a masked TTS-onset SEL level for a harbour porpoise subjected to single airgun transients, measuring auditory evoked potentials.…”

“…Lucke et al (2009) determined a masked TTS-onset SEL level for a harbour porpoise subjected to single airgun transients, measuring auditory evoked potentials. As the sound stimuli of Lucke et al resembled explosion sound better than other TTS studies currently available (Kastelein et al, 2012b(Kastelein et al, , 2014b(Kastelein et al, , 2015a(Kastelein et al, , 2015bTougaard et al, 2015), our estimates for SEL thresholds for TTS and PTS were based on that study.…”

“…Harbour porpoises have sensitive hearing, making them potentially exceptionally vulnerable to noise-induced effects from anthropogenic sound-producing activities at sea (Culik et al, 2001;Kastelein et al, 2002Kastelein et al, , 2010Kastelein et al, , 2012aKastelein et al, , 2012bKastelein et al, , 2013Kastelein et al, , 2014aKastelein et al, , 2014bKastelein et al, , 2015aKastelein et al, , 2015bKetten, 2004;Lucke et al, 2009;Tougaard et al, 2009). The main potential effects of concern of underwater explosions on an individual animal are (1) trauma (from direct or indirect blast wave effect injury) such as crushing, fracturing, hemorrhages, and rupture of body tissues caused by the blast wave, resulting in immediate or eventual mortality; (2) auditory impairment (from exposure to the acoustic wave), resulting in a temporary or permanent hearing loss such as temporary threshold shift (TTS) and permanent threshold shift (PTS); or (3) behavioural change, such as disturbance to feeding, mating, breeding, and resting.…”

Temporary hearing threshold shift in a harbor porpoise (Phocoena phocoena) after exposure to multiple airgun sounds

“…The hearing of porpoise 06 for sounds in the range of the hearing test signals used in the present study (0.5-8 kHz) was tested (Kastelein et al, 2017), and was found to be representative for animals of his age and species; his hearing thresholds were within a few dB of those obtained from other young male porpoises tested with behavioral methods (Kastelein et al, 2002;Kastelein et al, 2009;Kastelein et al, 2010;Kastelein et al, 2015b).…”

“…Besides the level of the sounds and the duration of the sequence, the duty cycle (signal duration, but especially the shot interval) can affect the induced TTS. Research has shown that the duty cycle of impulsive sounds affects the magnitude of TTS (Finneran et al, 2010;Kastelein et al, 2014a;Kastelein et al, 2015b), as hearing may recover, at least partly, between shots. Kastelein et al (2014a) reported that although exposure to a single sound did not lead to measurable TTS, the cumulative effect of sequences of sounds caused TTS.…”