Active Acoustics and Light Data from the Polar Night in Svalbard

• Main Authors: Berge, Jorgen, Geoffroy, Maxime
• Format: Dataset
• Language: unknown
• Published: Canadian Cryospheric Information Network 2019
• Subjects: Svalbard; Canada; Norway; Hanssen; polar night
• Online Access: https://dx.doi.org/10.21963/13104; https://www.polardata.ca/pdcsearch/PDCSearch.jsp?doi_id=13104

We tested the impact of artificial light from a research vessel on fish and zooplankton distribution and abundance during the polar night (January 2018) in Svalbard, Norway. All lights from the Helmer Hanssen were turned off for 49 min (January 9), 178 min (January 14) or 9 min (January 17) before being turned on again. Change in the acoustic backscatter was recorded from the hull-mounted EK60 (18 kHz, 38 kHz, and 120 kHz). The ping rate was set to maximum and pulse length to 1024 µs. The echosounder was calibrated using the standard sphere method. To measure the spatial impact of artificial light footprint from the ship, an Acoustic Zooplankton and Fish Profiler (AZFP 38 kHz, 125 kHz, 200 kHz, 455 kHz; ASL Environmental Science, Victoria, Canada) was deployed from a small boat (Polarcirkel™) stationary but at varying distances from the Helmer Hanssen. Vertical resolution varied from 37 cm on January 9 and 2 cm on January 14 and 17. The pulse duration was 1000 µs, ping rate 0.33 Hz (i.e. 1 ping 3 sec-1) and source level was 210 dB (re 1µPa at 1 m). The AZFP was calibrated by the manufacturer (± 1 dB) prior to deployment. The AZFP and EK60 echosounder on the Helmer Hanssen were operated at the same stations, but not at the same time to avoid interferences. Absorption and light backscatter profiles were recorded at 9 wavebands across the visible spectrum using WETLabs AC-9 and BB9 optical sensors respectively. Data from both instruments were corrected for light absorption and scattering artefacts following standard manufacturer’s correction methods. The AC-9 was calibrated using freshly drawn Milli-Q ultrapure water on board the ship. Temperature and salinity corrections were applied using concurrent data from Seabird SBE19Plus CTD profiles. Irradiance from ship’s lights at the sea surface was measured using a hyperspectral Trios RAMSES planar irradiance sensor, giving EPAR = 2.24 mol photons m-2 s-1 just beneath the surface. Retention of light (relative values) were measured using a set of specially designed sensors to measure light in situ during the Polar Night. Both fish and zooplankton were disturbed by normal working-light from a ship down to 200 m depth (limited by maximum water depth), and the potential impact area around the ship was >0.15 km2. We conclude that biological surveys in the dark from illuminated ships introduce biases on any sampling, bioacoustic surveys, and possibly stock assessments of commercial and non-commercial species.