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

• Published in: Marine Mammal Science
• Main Authors: Isojunno, Saana, von Benda-Beckmann, Alexander, Wensveen, Paul, Kvadsheim, Petter, Lam, Frans-Peter, Gkikopoulou, Kalliopi Charitomeni, Pöyhönen, Viivi, Tyack, Peter Lloyd, Benti, Benjamin, Foskolos, Ilias, Bort, Jacqueline, Neves, Miguel, Biassoni, Nicoletta, Miller, Patrick James
• Other Authors: University of St Andrews. School of Biology, University of St Andrews. Sea Mammal Research Unit, University of St Andrews. Scottish Oceans Institute, University of St Andrews. Centre for Social Learning & Cognitive Evolution, University of St Andrews. Marine Alliance for Science & Technology Scotland, University of St Andrews. Sound Tags Group, University of St Andrews. Bioacoustics group, University of St Andrews. Institute of Behavioural and Neural Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: Anthropogenic noise; Continuous active sonar; DTAG; Auditory masking; GC Oceanography; QH301 Biology; DAS; SDG 14 - Life Below Water; GC; QH301; Lombard; Sperm whale
• Online Access: http://hdl.handle.net/10023/26546; https://doi.org/10.1111/mms.12890

Funding: This work was supported by the UK Defense and Science Technology Laboratory (DSTLX-1000137649), NL Ministry of Defence (Cerema-DGA #1883003901), FR Ministry of Defence, and US Navy Living Marine Resources program (N39430-17-C-1935). PLT was supported by US Office of Naval Research (ONR) grant numbers N00014-18-1-2062 and N00014-20-1-2709, as well as by the Strategic Environmental Research and Development Program (SERDP) contracts RC20-1097, RC21-3091, and RC20-7188. 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. Postprint Postprint Peer reviewed