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      Signals from the deep: Spatial and temporal acoustic occurrence of beaked whales off western Ireland

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          Abstract

          Little is known of the spatio-temporal occurrence of beaked whales off western Ireland, limiting the ability of Regulators to implement appropriate management and conservation measures. To address this knowledge gap, static acoustic monitoring was carried out using eight fixed bottom-mounted autonomous acoustic recorders: four from May to December 2015 on Ireland’s northern slope and four from March to November 2016 on the western and southern slopes. Recorders ran for 205 to 230 days, resulting in 4.09 TB of data sampled at 250 kHz which could capture beaked whale acoustic signals. Zero-crossing-based automated detectors identified beaked whale clicks. A sample of detections was manually validated to evaluate and optimize detector performance. Analysis confirmed the occurrence of Sowerby’s and Cuvier’s beaked whales and Northern bottlenose whales. Northern bottlenose whale clicks occurred in late summer and autumn, but were too few to allow further analysis. Cuvier’s and Sowerby’s clicks occurred at all stations throughout the monitoring period. There was a significant effect of month and station (latitude) on the mean daily number of click detections for both species. Cuvier’s clicks were more abundant at lower latitudes while Sowerby’s were greater at higher latitudes, particularly in the spring, suggesting a spatial segregation between species, possibly driven by prey preference. Cuvier’s occurrence increased in late autumn 2015 off northwest Porcupine Bank, a region of higher relative occurrence for each species. Seismic airgun shots, with daily sound exposure levels as high as 175 dB re 1 μPa 2·s, did not appear to impact the mean daily number of Cuvier’s or Sowerby’s beaked whale click detections. This work provides insight into the significance of Irish waters for beaked whales and highlights the importance of using acoustics for beaked whale monitoring.

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          Evaluation: from precision, recall and f-measure to roc, informedness, markedness & correlation

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            Beaked Whales Respond to Simulated and Actual Navy Sonar

            Beaked whales have mass stranded during some naval sonar exercises, but the cause is unknown. They are difficult to sight but can reliably be detected by listening for echolocation clicks produced during deep foraging dives. Listening for these clicks, we documented Blainville's beaked whales, Mesoplodon densirostris, in a naval underwater range where sonars are in regular use near Andros Island, Bahamas. An array of bottom-mounted hydrophones can detect beaked whales when they click anywhere within the range. We used two complementary methods to investigate behavioral responses of beaked whales to sonar: an opportunistic approach that monitored whale responses to multi-day naval exercises involving tactical mid-frequency sonars, and an experimental approach using playbacks of simulated sonar and control sounds to whales tagged with a device that records sound, movement, and orientation. Here we show that in both exposure conditions beaked whales stopped echolocating during deep foraging dives and moved away. During actual sonar exercises, beaked whales were primarily detected near the periphery of the range, on average 16 km away from the sonar transmissions. Once the exercise stopped, beaked whales gradually filled in the center of the range over 2–3 days. A satellite tagged whale moved outside the range during an exercise, returning over 2–3 days post-exercise. The experimental approach used tags to measure acoustic exposure and behavioral reactions of beaked whales to one controlled exposure each of simulated military sonar, killer whale calls, and band-limited noise. The beaked whales reacted to these three sound playbacks at sound pressure levels below 142 dB re 1 µPa by stopping echolocation followed by unusually long and slow ascents from their foraging dives. The combined results indicate similar disruption of foraging behavior and avoidance by beaked whales in the two different contexts, at exposures well below those used by regulators to define disturbance.
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              First direct measurements of behavioural responses by Cuvier's beaked whales to mid-frequency active sonar

              Most marine mammal­ strandings coincident with naval sonar exercises have involved Cuvier's beaked whales (Ziphius cavirostris). We recorded animal movement and acoustic data on two tagged Ziphius and obtained the first direct measurements of behavioural responses of this species to mid-frequency active (MFA) sonar signals. Each recording included a 30-min playback (one 1.6-s simulated MFA sonar signal repeated every 25 s); one whale was also incidentally exposed to MFA sonar from distant naval exercises. Whales responded strongly to playbacks at low received levels (RLs; 89–127 dB re 1 µPa): after ceasing normal fluking and echolocation, they swam rapidly, silently away, extending both dive duration and subsequent non-foraging interval. Distant sonar exercises (78–106 dB re 1 µPa) did not elicit such responses, suggesting that context may moderate reactions. The observed responses to playback occurred at RLs well below current regulatory thresholds; equivalent responses to operational sonars could elevate stranding risk and reduce foraging efficiency.
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                Author and article information

                Contributors
                Role: Formal analysisRole: InvestigationRole: ResourcesRole: ValidationRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Formal analysisRole: MethodologyRole: VisualizationRole: Writing – review & editing
                Role: ConceptualizationRole: MethodologyRole: SoftwareRole: VisualizationRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: MethodologyRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: ConceptualizationRole: Funding acquisitionRole: Project administrationRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: Funding acquisitionRole: MethodologyRole: Project administrationRole: SupervisionRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                21 June 2018
                2018
                : 13
                : 6
                : e0199431
                Affiliations
                [1 ] JASCO Applied Sciences, Dartmouth, Nova Scotia, Canada
                [2 ] Marine and Freshwater Research Centre, Galway-Mayo Institute of Technology, Galway, Ireland
                [3 ] National Parks & Wildlife Service, Department of Culture, Heritage and the Gaeltacht, Dublin, Ireland
                Evergreen State College, UNITED STATES
                Author notes

                Competing Interests: Our affiliation with JASCO Applied Sciences does not alter our adherence to PLOS ONE policies on sharing data and materials.

                Author information
                http://orcid.org/0000-0002-1325-8321
                http://orcid.org/0000-0003-0296-2660
                Article
                PONE-D-18-05013
                10.1371/journal.pone.0199431
                6013249
                29928009
                7ee71fe3-91ad-4f9d-9577-363dff70d00d
                © 2018 Kowarski et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 16 February 2018
                : 7 June 2018
                Page count
                Figures: 12, Tables: 6, Pages: 26
                Funding
                This study is part of the ObSERVE Acoustic project that was initiated and funded by the Department of Communications, Climate Action and Environment in partnership with the Department of Culture, Heritage and the Gaeltacht under Ireland’s ObSERVE Programme. The Galway-Mayo Institute of Technology (GMIT) is the lead organization in ObSERVE. JASCO Applied Sciences was contracted by GMIT to provide acoustic recorders, analysis services, and to prepare a final report, but did not have any additional role in the study design, data collection, or decision to publish. JASCO provided internal funding in the form of salaries for authors (KK, JD, and BM) to prepare the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.
                Categories
                Research Article
                Biology and Life Sciences
                Organisms
                Eukaryota
                Animals
                Vertebrates
                Amniotes
                Mammals
                Marine Mammals
                Whales
                Beaked Whales
                Biology and Life Sciences
                Marine Biology
                Marine Mammals
                Whales
                Beaked Whales
                Earth Sciences
                Marine and Aquatic Sciences
                Marine Biology
                Marine Mammals
                Whales
                Beaked Whales
                Physical Sciences
                Physics
                Acoustics
                Bioacoustics
                Biology and Life Sciences
                Bioacoustics
                Biology and Life Sciences
                Behavior
                Animal Behavior
                Foraging
                Biology and Life Sciences
                Zoology
                Animal Behavior
                Foraging
                Physical Sciences
                Physics
                Acoustics
                Acoustic Signals
                Earth Sciences
                Geography
                Cartography
                Latitude
                Biology and Life Sciences
                Behavior
                Engineering and Technology
                Remote Sensing
                Sonar
                People and places
                Geographical locations
                Europe
                European Union
                Ireland
                Custom metadata
                Beaked whale occurrence results from automated detectors and manual analysis are provided in spreadsheet form as Supporting Information. Therefore, all information necessary to replicate our study is available. The raw acoustic data cannot be made readily available due to size limitations (more than 17 TB). The acoustic data is owned by the Irish Department of Communications, Climate Action and Environment. The authors were given no special access privileges to the acoustic data and requests for access to the entirety of the raw acoustic data from ObSERVE (in the same manner as the authors) can be submitted to PADadmin@ 123456DCCAE.gov.ie .

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