Diving behaviour of Cuvier's beaked whales exposed to two types of military sonar.

Erin A Falcone,Russel D Andrews,Alexandre N Zerbini,Stacy L Deruiter,Ronald P Morrissey,David J Moretti,Gregory S Schorr,Stephanie L Watwood

doi:10.1098/rsos.170629

Abstract

Cuvier's beaked whales (Ziphius cavirostris) have stranded in association with mid-frequency active sonar (MFAS) use, and though the causative mechanism linking these events remains unclear, it is believed to be behaviourally mediated. To determine whether MFAS use was associated with behavioural changes in this species, satellite tags were used to record the diving and movements of 16 Cuvier's beaked whales for up to 88 days in a region of frequent MFAS training off the coast of Southern California. Tag data were combined with summarized records of concurrent bouts of high-power, surface-ship and mid-power, helicopter-deployed MFAS use, along with other potential covariates, in generalized additive mixed-effects models. Deep dives, shallow dives and surface intervals tended to become longer during MFAS use, with some variation associated with the total amount of overlapping MFAS during the behaviour. These changes in dives and surface intervals contributed to a longer interval between deep dives, a proxy for foraging disruption in this species. Most responses intensified with proximity and were more pronounced during mid-power than high-power MFAS use at comparable distances within approximately 50 km, despite the significantly lower source level of mid-power MFAS. However, distance-mediated responses to high-power MFAS, and increased deep dive intervals during mid-power MFAS, were evident up to approximately 100 km away.

Highlights

Beaked whale species (Family Ziphiidae) have been observed to strand in association with the use of midfrequency active sonars, such as those used by military vessels around the world to search for quiet submarines [1,2,3]
The use of extended-duration tags with acoustic recording capability, currently under development, could provide vocalization data from the tagged whale itself, and would be the best way to verify foraging activity during deep dives in the future. Exposure to both high- and mid-power military mid-frequency active sonar (MFAS) systems was associated with a variety of behavioural changes in satellite-tagged Cuvier’s beaked whales in the Southern California Bight
Responses that increased with proximity were evident up to 100 km away in this large dataset that included sizeable samples of behaviour from 16 whales during periods both with and without MFAS use, despite the relative coarseness of both the behavioural and MFAS data used in this analysis

Summary

Introduction

Beaked whale species (Family Ziphiidae) have been observed to strand in association with the use of midfrequency active sonars (hereafter ‘MFAS’), such as those used by military vessels around the world to search for quiet submarines [1,2,3]. Current methods for estimating the impacts of MFAS use on beaked whales involve considerable uncertainty, and few suitable approaches have been identified to mitigate these risks. Beaked whales were minimally studied prior to 1999, when interest in these species increased following the aforementioned MFAS-associated stranding events. Of the small number of species that have been fitted with dive-recording tags, Cuvier’s beaked whales (Ziphius cavirostris), in particular, have conducted dives far exceeding those of any other mammal in both depth and duration [16]

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Results

Discussion

Conclusion