Threshold received sound pressure levels of single 1–2 kHz and 6–7 kHz up-sweeps and down-sweeps causing startle responses in a harbor porpoise (Phocoena phocoena)

Abstract

Mid-frequency and low-frequency sonar systems produce frequency-modulated sweeps which may affect harbor porpoises. To study the effect of sweeps on behavioral responses (specifically "startle" responses, which we define as sudden changes in swimming speed and/or direction), a harbor porpoise in a large pool was exposed to three pairs of sweeps: a 1-2 kHz up-sweep was compared with a 2-1 kHz down-sweep, both with and without harmonics, and a 6-7 kHz up-sweep was compared with a 7-6 kHz down-sweep without harmonics. Sweeps were presented at five spatially averaged received levels (mRLs; 6 dB steps; identical for the up-sweep and down-sweep of each pair). During sweep presentation, startle responses were recorded. There was no difference in the mRLs causing startle responses for up-sweeps and down-sweeps within frequency pairs. For 1-2 kHz sweeps without harmonics, a 50% startle response rate occurred at mRLs of 133 dB re 1 μPa; for 1-2 kHz sweeps with strong harmonics at 99 dB re 1 μPa; for 6-7 kHz sweeps without harmonics at 101 dB re 1 μPa. Low-frequency (1-2 kHz) active naval sonar systems without harmonics can therefore operate at higher source levels than mid-frequency (6-7 kHz) active sonar systems without harmonics, with similar startle effects on porpoises.

Effect of level, duration, and inter-pulse interval of 1–2 kHz sonar signal exposures on harbor porpoise hearing

“…The 50% detection level of LFAS signals is at 75 dB re 1 lPa (Kastelein et al, 2011), and the received SPL needs to be 60 dB higher ($135 dB re 1 lPa) before porpoises respond behaviorally (in 50% of the exposures) to emitted single LFAS signals (Kastelein et al, 2012c). So far, three published studies have documented research on TTS in harbor porpoises.…”

Exposure amplitude and repetition affect bottlenose dolphin behavioral responses to simulated mid-frequency sonar signals

“…Protecting marine mammals from the potential impact of anthropogenic sound exposure is difficult because little is known about the consequences of sound exposure to marine mammals and evidence suggests considerable variation in individual and species tolerances and reactions to introduced sound (Diaz López and Mariño, 2011;Finneran et al, 2003;Holst et al, 2011;Holt et al, 2011;Johnston, 2002;Kastelein et al, 2012;McCarthy et al, 2011;Miksis-Olds and Wagner, 2011;Miksis-Olds et al, 2007;Miller et al, 2009;Morton and Symonds, 2002;Niu et al, 2012;Nowacek et al, 2004;Olesiuk et al, 2002;Parks et al, 2007;Tyack et al, 2011). Ultimately, it is the mapping of changes in natural behaviors as a result of anthropogenic sound exposure to potential fitness consequences that is of interest (National Research Council (NRC), 2005).…”

Hearing frequency thresholds of a harbor porpoise (Phocoena phocoena) temporarily affected by a continuous 1.5 kHz tone

“…The hearing sensitivity of harbor porpoises increases greatly between 0.2 and 60 kHz, so the sensation level (i.e., the SPL above the basic hearing threshold for a particular frequency) of harmonics may be higher than the sensation level of the fundamental sound. Kastelein et al (2011) showed that the hearing threshold of a harbor porpoise for a 1-2 kHz sweep with harmonics may be much lower than the threshold for the same sweep without harmonics, and that harbor porpoises may be disturbed more by sounds with harmonics than by sounds without (Kastelein et al, 2012c). In addition, TTS sensitivity may be frequency-dependent; increased sensitivity with frequency was observed in bottlenose dolphins (Finneran and Schlundt, 2010).…”