Estimation of changes in behaviour of narwhals

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 1) ship noise and 2) concurrent ship noise and airgun pulses.

Methods
The sound exposure program was operated from an offshore patrol vessel HDMS Lauge Koch 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 in3) 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.

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 AcousondeTM 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 6 columns: 1) Ind: unique name for individual whale, 2) Depth: depth (m), 3) GPS_time, 4) Buzz: 0 or 1. 1 indicates a start of buzz in that second, 0 indicates no buzz. Buzzes were detected as described above, 5) X: exposure value (1/distance between ship and whale km) during exposure to ship with concurrent airgun pulses, 6) P: exposure value (1/distance between ship and whale km) during exposure to ship.