Auditory impairment from acoustic seal deterrents predicted for harbour porpoises in a marine protected area
Findlay, Charlotte et al. (2021), Auditory impairment from acoustic seal deterrents predicted for harbour porpoises in a marine protected area, Dryad, Dataset, https://doi.org/10.5061/dryad.j6q573ndq
1. Management interventions to reduce human-wildlife conflict can have unintended consequences for non-target species. Acoustic deterrent devices (ADDs) are used globally by the aquaculture sector. However, the potential for these sound emissions to impact non-target species, such as cetaceans, has not yet been quantified at population relevant spatial scales.
2. To better understand the extent of potential impacts on cetaceans, such as harbour porpoises, we used acoustic modelling to investigate levels of ADD noise throughout the west coast of Scotland and across a Special Area of Conservation (SAC) for this species.
3. Using an energy-flux acoustic propagation model and data on aquaculture sites known to be using ADDs, we predicted the spatial extent of ADD noise on the Scottish west coast from the 1st February 2017 to 31st January 2018. Noise maps were produced to determine the risk of auditory impairment for harbour porpoises under a range of scenarios which assumed single or multiple ADDs and simultaneous use across all sites.
4. The acoustic propagation model performed well when tested against field measurements up to 5 km, with 98% of sound exposure level (SEL) predictions within ±10% of the measurements. Predictions of SELs over a 24-hour period suggested extensive temporary hearing loss zones (median radius: ~28 km) for harbour porpoises around aquaculture sites. Assuming a single device at each site, 23% of the harbour porpoise SAC was predicted to be exposed to ADD noise sufficient to induce a temporary threshold shift, and under the worst-case scenario (multiple, continuously running devices per site with an aggregate duty cycle of 100%), levels exceeding permanent threshold shift could reach 0.9% of the SAC.
5. Policy implications. This study highlights the potential for ‘collateral damage’ from interventions such as acoustic deterrent devices (ADDs) which are intended to reduce human-wildlife conflicts with pinnipeds but may affect the long-term health and habitat use of non-target species. This is especially true for harbour porpoises which are protected under the EU and UK Habitats Regulations. The aquaculture industry, policymakers and regulators in countries where ADDs are used should consider these findings when attempting to mitigate pinniped depredation.
Locations of aquaculture sites on the west coast of Scotland using Acoustic Deterrent Devices (ADDs) were obtained from information submitted to the Marine Scotland – Licensing Operations Team in fulfilment of seal shooting license applications (NatureScot, 2018), and consequently may not include all sites using ADDs in 2017. Aquaculture site names have been redacted but data includes the source locations (latitude and longitude in decimal degrees), ADD type deployed (Ace Aquatec US3, Airmar, Terecos Type DSMS-4 and OTAQ SealFence) and whether or not sites were included (Y/N) in model simulations.
The excel file contains the measured and modelled sound exposure levels (SELs; dB re 1 dB re 1 µPa2s over 1-second) for 8, 10 and 12.5 kHz 1/3 Octave Frequency Bands (TOBs) produced by a Gael Force SeaGuard ADD (https://www.gaelforcegroup.com) which was deployed at three sites on the west coast of Scotland (1: Firth of Lorne; 2: Sound of Kerrera; and 3: Loch Etive). Measurements were made at intervals of ~100 m up to 1 km, and then at 2 and 5 km, in four directions around the device using a SoundTrap 300 HF (sensitivity -188.4 dB re 1 V/mPa; Ocean Instruments Ltd.) sampling at 144 kHz, suspended at 10 m depth (true distances and distance bins [100 m and 1000 m] between the ADD and each measurement are included in this file).
It should be noted that the validation experiment was set up with the intention of measuring propagation loss with distance in environments similar to those where aquaculture sites are located and not to measure the source levels of the Gael Force SeaGuard ADD. Source levels of the Gael Force SeaGuard ADD were lower than expected due to the coiling of a 30 m cable to deploy the device to 10 m and therefore may not be representative of source levels produced by other Gael Force SeaGuard ADDs.
If you wish to obtain additional data (e.g., shapefiles of acoustic propagation model outputs) or code please contact the corresponding author of this publication.
European Social Fund
Scottish Funding Council
Centre for Environment, Fisheries and Aquaculture Science