Northern bottlenose whales in a pristine environment respond strongly to close and distant navy sonar signals.

Paul J Wensveen,Saana Isojunno,Peter L Tyack,Frans-Peter A Lam,Stacy L Deruiter,Tomoko Narazaki,Charlotte Curé,Rune R Hansen,Petter H Kvadsheim,Lars Kleivane,Patrick J O Miller,Sander Van Ijsselmuide,Alexander M Von Benda-Beckmann

doi:10.1098/rspb.2018.2592

Abstract

Impact assessments for sonar operations typically use received sound levels to predict behavioural disturbance in marine mammals. However, there are indications that cetaceans may learn to associate exposures from distant sound sources with lower perceived risk. To investigate the roles of source distance and received level in an area without frequent sonar activity, we conducted multi-scale controlled exposure experiments (n = 3) with 12 northern bottlenose whales near Jan Mayen, Norway. Animals were tagged with high-resolution archival tags (n = 1 per experiment) or medium-resolution satellite tags (n = 9 in total) and subsequently exposed to sonar. We also deployed bottom-moored recorders to acoustically monitor for whales in the exposed area. Tagged whales initiated avoidance of the sound source over a wide range of distances (0.8–28 km), with responses characteristic of beaked whales. Both onset and intensity of response were better predicted by received sound pressure level (SPL) than by source distance. Avoidance threshold SPLs estimated for each whale ranged from 117–126 dB re 1 µPa, comparable to those of other tagged beaked whales. In this pristine underwater acoustic environment, we found no indication that the source distances tested in our experiments modulated the behavioural effects of sonar, as has been suggested for locations where whales are frequently exposed to sonar.

Highlights

Marine mammals rely on sound for their survival and may be affected by anthropogenic noise in their environment
Change-points were not identified in the Mahalanobis distances (MDs) metrics for avoidance and change in locomotion
This study aimed to describe factors affecting responses of beaked whales to sonar in a remote area with little naval sonar activity; an area that can be considered acoustically pristine when compared with locations where similar studies have been conducted

Summary

Introduction

Marine mammals rely on sound for their survival and may be affected by anthropogenic noise in their environment. Negative impacts of noise may include hearing loss [1], auditory masking [2], displacement [3] and disruption of important behaviours such as foraging and resting [4], with potential cumulative long-term population-level effects [5]. Recent studies on effects of anthropogenic noise within the marine environment have focused on the vulnerability of mammals to various disturbance sources, including naval sonar [6]. Several atypical mass strandings of predominantly beaked whales have occurred in close spatio-temporal proximity to sonar exercises [7].

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