DOI: 10.5061/dryad.000000046
title: Narwhals react to ship noise and airgun pulses embedded in background noise

description: Anthropogenic activities are increasing in the Arctic posing a threat to
 species with high seasonal site-fidelity, such as the narwhal Monodon
 monoceros. In this controlled sound exposure study, six narwhals were
 live-captured and instrumented with animal-borne tags providing movement
 and behavioural data, and exposed to concurrent ship noise and airgun
 pulses. All narwhals reacted to sound exposure by reduced buzzing rates,
 where the response was dependent on the magnitude of exposure defined as
 1/distance to ship. Halving of buzzing rate, compared with undisturbed
 behaviour, and cessation of foraging occurred at 12 and ~7-8 km from the
 ship, respectively. The effect of exposure could be detected &gt; 40
 km from the ship. At distances &gt; 5 km, the received high-frequency
 cetacean weighted sound exposure levels were below background noise
 indicating sensitivity of narwhals towards sound disturbance and
 demonstrating their ability to detect signals embedded in noise. Further
 studies are needed to evaluate the energetic costs of disrupted foraging
 due to sustained disturbance but the observed sensitivity should be
 considered in the management of anthropogenic activities in the Arctic.
 The results of this study emphasize the importance of controlled sound
 exposure studies in the wild to explore the auditory capabilities of
 odontocetes.
description: Six male narwhals were live-captured in August 2018 in the
 Scoresby Sound fjord system in East Greenland. The data were collected
 using animal-borne Acousonde<sup>TM</sup> acoustic and
 orientation recorders and backpack FastLoc GPS-receivers (Wildlife
 Computers (Redmond, Seattle, WA, USA) collecting an unrestricted number of
 FastLoc snapshots through August 2018. Acousondes were set to collect
 triaxial acceleration and orientation (sf 100 Hz), depth (sf 10 Hz), and
 acoustics. Acoustics was sampled continuously with a 25 811 Hz sampling
 rate (HTI-96-MIN hydrophone, nominal sensitivity -201 dB re 1 V / μ Pa,
 preamp gain 14 dB, an anti-aliasing filter with 3-dB reduction at 9.2 kHz
 and 22-dB reduction at 11.1 kHz, 16-bit resolution).
 The dataset has been processed as follows: Time-depth records
 were down-sampled to 1 Hz and time-synchronized with GPS positions.
 Additional GPS positions were created for each second between successive
 positions through linear interpolation. Buzzes were used as a proxy for
 foraging attempts and were detected using a custom-written detector
 (Matlab, The MathWorks, Inc., Natick, MA, USA) and verified manually. When
 the sound source and animal were within line of sight (determined visually
 from maps showing the positions of the ships and whales aligned in time),
 distance between the whale and the sound source was determined for each
 second. The dataset is comprised of 5 columns: 1) Ind:
 unique name for individual whale, 2) Buzz: 0 or 1. 1 indicates a start of
 buzz in that second, 0 indicates no buzz. Buzzes were detected as
 described above. 3) Seismik: 0 or 1. 1 indicates that the seimic airgun
 used in the experiment was active, 0 indicates times when it was not
 active. 4): LOS: short for line of sight. 0 or 1. 1 indcates times when
 the individual and the sound source were within line of sight, 0 indicates
 times when the whale and sound source were not within line of sight. 5)
 Dist_ship: distance between whale and sound source in meters (m).
 Calculated only when LOS=1. NA indicates times when the whale and sound
 source were not within line of sight.
description: The seismic program was operated from an offshore patrol vessel
 HDMS <i>Lauge Koch</i> equipped with a Reson Seabat 7160
 multibeam echo sounder (MBES) (nominal operating frequency 41–47 kHz),
 that ran continuously. The airgun setup included a cluster of two Sercel
 G-guns (17.0 l (1040 in<sup>3</sup>) in total) towed at 6 m depth and operated at a mean pressure of 125 bar. The guns in the cluster were fired synchronously every 80 seconds during trials, lasting 3–8 hours, while the ship’s GPS navigation system recorded the location of every shot.