Co-occurrence of beaked whale strandings and naval sonar in the Mariana Islands, Western Pacific

Mid-frequency active sonar (MFAS), used for antisubmarine warfare (ASW), has been associated with multiple beaked whale (BW) mass stranding events. Multinational naval ASW exercises have used MFAS offshore of the Mariana Archipelago semi-annually since 2006. We report BW and MFAS acoustic activity near the islands of Saipan and Tinian from March 2010 to November 2014. Signals from Cuvier's (Ziphius cavirostris) and Blainville's beaked whales (Mesoplodon densirostris), and a third unidentified BW species, were detected throughout the recording period. Both recorders documented MFAS on 21 August 2011 before two Cuvier's beaked whales stranded on 22-23 August 2011. We compared the history of known naval operations and BW strandings from the Mariana Archipelago to consider potential threats to BW populations. Eight BW stranding events between June 2006 and January 2019 each included one to three animals. Half of these strandings occurred during or within 6 days after naval activities, and this co-occurrence is highly significant. We highlight strandings of individual BWs can be associated with ASW, and emphasize the value of ongoing passive acoustic monitoring, especially for beaked whales that are difficult to visually detect at sea. We strongly recommend more visual monitoring efforts, at sea and along coastlines, for stranded cetaceans before, during and after naval exercises.

A. E. Simonis, R. L. Brownell, B. J. Thayre, J. S. Trickey, E. M. Oleson, R. Huntington, et al. Proceedings of the Royal Society B: Biological Sciences 2020 Vol. 287 Issue 1921 Pages 20200070 DOI: 10.1098/rspb.2020.0070

Anne E. Simonis 1, Robert L. Brownell Jr. 2, Bruce J. Thayre 3, Jennifer S. Trickey 3, Erin M. Oleson 4, Roderick Huntington 3,5, Kristi L. West 6,7, Simone Baumann-Pickering 3

1 Contractor to Pacific Islands Fisheries Science Center, National Oceanic and Atmospheric Administration

2 Southwest Fisheries Science Center, National Oceanic and Atmospheric Administration

3 Scripps Institution of Oceanography, UCSD

4 Pacific Islands Fisheries Science Center, National Oceanic and Atmospheric Administration

5 Mount Edgecumbe High School

6 Hawaii Institute of Marine Biology, University of Hawaii at Manoa, PO Box 1346, Kaneohe, HI 96744

7 Department of Human Nutrition Food and Animal Science, College of Tropical Agriculture and Human Resources, 1955 East-West Road, University of Hawaii at Manoa Ag Sci 216, Honolulu, HI 96822

Corresponding author: Anne Simonis, anne.simonis@gmail.com