When the noise goes on : received sound energy predicts sperm whale responses to both intermittent and continuous navy sonar
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Anthropogenic noise sources range from intermittent to continuous, with seismic and navy sonar technology moving towards near-continuous transmissions. Continuous active sonar (CAS) may be used at a lower amplitude than traditional pulsed active sonar (PAS), but potentially with greater cumulative sound energy. We conducted at-sea experiments to contrast the effects of navy PAS versus CAS on sperm whale behaviour using animal-attached sound- and movement-recording tags (n=16 individuals) in Norway. Changes in foraging effort and proxies for foraging success and cost during sonar and control exposures were assessed while accounting for baseline variation [individual effects, time of day, bathymetry and blackfish (pilot/killer whale) presence] in generalized additive mixed models (GAMMs). We found no reduction in time spent foraging during exposures to medium-level PAS (MPAS) transmitted at the same peak amplitude as CAS. In contrast, we found similar reductions in foraging during CAS (d.f.=1, F=8.0, P=0.005) and higher amplitude PAS (d.f.=1, F=20.8, P<0.001) when received at similar energy levels integrated over signal duration. These results provide clear support for sound energy over amplitude as the response driver. We discuss the importance of exposure context and the need to measure cumulative sound energy to account for intermittent versus more continuous sources in noise impact assessments.
Isojunno , S , Wensveen , P , Lam , F-P , Kvadsheim , P , von Brenda-Beckmann , A M , Martín López , L M , Kleivane , L , Siegal , E & Miller , P 2020 , ' When the noise goes on : received sound energy predicts sperm whale responses to both intermittent and continuous navy sonar ' , Journal of Experimental Biology , vol. 223 , no. 7 , jeb219741 . https://doi.org/10.1242/jeb.219741
Journal of Experimental Biology
Copyright © 2020 The Author(s). Published by The Company of Biologists Ltd http://creativecommons.org/licenses/by/4.0This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
DescriptionThis work was supported by the UK Defence Science and Technology Laboratory, The Netherlands Ministry of Defence, French Ministry of Defence, and US Navy Living Marine Resources program (contract No. N39430-17-C-1935). Open access funding provided by the University of St Andrews. Deposited in PMC for immediate release.
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