Sperm whales exhibit variation in echolocation tactics with depth and sea state but not naval sonar exposures

Saana Isojunno*, Alexander M. von Benda-Beckmann, Paul J. Wensveen, Petter H. Kvadsheim, Frans-Peter A. Lam, Kalliopi Gkikopoulou, Viivi Pöyhönen, Peter L. Tyack, Benjamin Benti, Ilias Foskolos, Jacqueline Bort, Miguel Neves, Nicoletta Biassoni, Patrick J. O. Miller

*Corresponding author for this work

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review

Abstract

Auditory masking by anthropogenic noise may impact marine mammals relying on sound for important life functions, including echolocation. Animals have evolved antimasking strategies, but they may not be completely effective or cost-free. We formulated seven a priori hypotheses on how odontocete echolocation behavior could indicate masking. We addressed six of them using data from 15 tagged sperm whales subject to experimental exposures of pulsed and continuous active sonar (PAS and CAS). Sea state, received single-pulse sound exposure level (SELsp), whale depth and orientation towards surface, and sonar were considered as candidate covariates representing different masking conditions. Echolocation behavior, including buzz duration and search range, varied strongly with depth. After controlling for depth and angle to the surface, the likelihood of buzzing following a click train decreased with sea state (t = −7.3, p < .001). There was little evidence for changes in 10 tested variables with increasing sonar SELsp, except reduced buzzing consistent with previously reported feeding cessation (t = −2.26, p = .02). A potential Lombard effect was detected during echolocation with sea state and SELsp, despite off-axis measurement and right-hand censoring due to acoustic clipping. The results are not conclusive on masking effects on sperm whale echolocation, highlighting challenges and opportunities for future anthropogenic masking studies.
Original languageEnglish
JournalMarine Mammal Science
Volume38
Issue2
Pages (from-to)682-704
Number of pages23
ISSN0824-0469
DOIs
Publication statusPublished - 6 Dec 2021

Keywords

  • anthropogenic noise
  • continuous active sonar
  • DTAG
  • auditory masking

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