title: 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.
authors.affiliation: Sea Mammal Research Company, Julianalaan 46, 3843 CC Harderwijk, The Netherlands. researchteam@zonnet.nl
authors.forename: Ronald A
authors.initials: RA
authors.lastname: Kastelein
authors.forename: Nele
authors.initials: N
authors.lastname: Steen
authors.forename: Robin
authors.initials: R
authors.lastname: Gransier
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Wensveen
authors.forename: Christ A F
authors.initials: CA
authors.lastname: de Jong
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000162:Acoustics / Q000295:instrumentation; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology*; D001522:Behavior, Animal; D008297:Male; D050741:Phocoena / Q000502:physiology*; D013216:Reflex, Startle / Q000502:physiology*; D013016:Sound / Q000009:adverse effects*; D013018:Sound Spectrography