Pile driving playback sounds and temporary threshold shift in harbor porpoises (Phocoena phocoena): Effect of exposure duration

Abstract

High intensity underwater sounds may cause temporary hearing threshold shifts (TTSs) in harbor porpoises, the magnitude of which may depend on the exposure duration. After exposure to playbacks of pile driving sounds, TTSs in two porpoises were quantified at 4 and 8 kHz with a psychophysical technique. At 8 kHz, the pile driving sounds caused the highest TTS. Pile driving sounds had the following: pulse duration 124 ms, rate 2760 strikes/h, inter-pulse interval 1.3 s, duty cycle ∼9.5%, average received single-strike unweighted broadband sound exposure level (SELss) 145 dB re 1 μPa(2)s, exposure duration range 15-360 min (cumulative SEL range: 173-187 dB re 1 μPa(2)s). Control sessions were also carried out. Mean TTS (1-4 min after sound exposure stopped in one porpoise, and 12-16 min in the other animal) increased from 0 dB after 15 min exposure to 5 dB after 360 min exposure. Recovery occurred within 60 min post-exposure. For the signal duration, sound pressure level (SPL), and duty cycle used, the TTS onset SELcum is estimated to be around 175 dB re 1 μPa(2)s. The small increase in TTS between 15 and 360 min exposures is due to the small amount of sound energy per unit of time to which the porpoises were exposed [average (over time) broadband SPL ∼144 dB re 1 μPa].

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

“…In the present study, no significant difference was observed in the mean TTS after exposure of the study animal to 10 successive double airgun shots and 20 successive double airgun shots (Table IV). Kastelein et al (2016b) observed only a very small increase in TTS (the ratio of TTS increase to the associated increase in SELcum was $ 0.5 dB/dB) between 30 min and 6 h exposures of harbor porpoises to impulsive pile driving playback sounds (1.3 s inter-pulse intervals, duty cycle $9.5%). The same phenomenon was observed in other TTS studies in which harbor porpoises were exposed to intermittent fatiguing sounds and continuous sounds (Kastelein et al, 2014a;Kastelein et al, 2016a).…”

“…First, a recording of a single pile driving sound (an impulsive sound that was used as a substitute for airgun sounds during the training phase) was played back via an underwater transducer (Lubell LL1424HP; see Fig. 1 for position) up to the level of a SELss of 145 dB re 1 lPa 2 s (see Kastelein et al, 2016b).…”

“…While TTS has not been demonstrated in harbor porpoises following exposure to multiple seismic sounds, it has been shown following exposure to pile driving sounds. TTS in harbor porpoises has previously been induced by exposure to long (1-6 h) sequences of playbacks of impulsive pile driving sounds (produced during the installation of wind turbines at sea; Kastelein et al, 2015a;Kastelein et al, 2016b).…”

“…It has not been demonstrated that frequency selective weighting of the SEL allows for reliable prediction of TTS onset in harbor porpoises exposed to impulsive sound. Pile driving playback studies with harbor porpoises measured TTS induced by repetitive impulsive sounds (Kastelein et al, 2016b), but differences in the durations, intervals and numbers of shots make it hard to extrapolate these observations to airgun exposures with longer shot intervals. Therefore, a harbor porpoise was exposed to custom-built down-scaled airguns.…”

Seal Bomb Noise as a Potential Threat to Monterey Bay Harbor Porpoise

“…However, published records of VHF-weighted SELs of seal bombs are lacking. Among the stimuli studied for harbor porpoises, pile driving and seismic airguns are most similar to seal bombs due to their high-intensity, broadband impulses with strong lowfrequency components (Hermannsen et al, 2015;Kastelein et al, 2016). Thresholds for TTS and PTS in "Very High-Frequency" odontocetes including harbor porpoises, have been based on studies of these stimuli (Southall et al, 2019).…”