When the noise goes on: received sound energy predicts sperm whale responses to both intermittent and continuous navy sonar

Saana Isojunno*, Paul Wensveen, Frans-Peter Lam, Petter Kvadsheim, Alexander M. von Brenda-Beckmann, Lucía Martina Martín López, Lars Kleivane, Eilidh Siegal, Patrick Miller

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)
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Abstract

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.
Original languageEnglish
Article numberjeb219741
Number of pages10
JournalJournal of Experimental Biology
Volume223
Issue number7
DOIs
Publication statusPublished - 8 Apr 2020

Keywords

  • Anthropogenic noise
  • Continuous active sonar
  • DTAG
  • Intermittent sound
  • Time budget
  • Time-series model

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