Narwhals react to ship noise and airgun pulses embedded in background noise

• Main Authors: Tervo, Outi, Blackwell, Susanna, Ditlevsen, Susanne, Conrad, Alexander, Samson, Adeline, Garde, Eva, Hansen, Rikke, Heide-Jørgensen, Mads Peter
• Format: Dataset
• Language: unknown
• Published: 2021
• Subjects: narwhal; airgun; Arctic; foraging; Greenland; Scoresby; East Greenland; Monodon monoceros; narwhal*; Scoresby Sound
• Online Access: https://zenodo.org/record/5181455; https://doi.org/10.5061/dryad.000000046

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 > 40 km from the ship. At distances > 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. The seismic 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 ...