Exposure of individual harbour seals (Phoca vitulina) and waters surrounding protected habitats to acoustic deterrent noise from aquaculture
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Date
2022-02
Journal Title
Journal ISSN
Volume Title
Publisher
John Wiley & Sons Ltd.
Abstract
1. Pinniped depredation at aquaculture sites is a globally recognized problem. To
mitigate depredation, the aquaculture sector uses acoustic deterrent devices (ADDs)
as a non-lethal alternative to shooting pinnipeds interacting with caged finfish.
However, it is unclear whether sound emissions from ADDs have the potential
to also impact non-target pinnipeds at spatial scales relevant to populations.
2. Global Positioning System (GPS) tracking data from seven harbour seals tagged in
a non-aquaculture context, on the west coast of Scotland, in 2017 were
combined with modelled maps of ADD noise to quantify sound exposure and
estimate the potential for auditory impairment. The acoustic model applied an
energy flux approach across the main frequency range of ADDs (2–40 kHz).
Predictions of temporary and permanent auditory threshold shifts were made
using seal location data and published noise exposure criteria. The acoustic
exposure of waters (10-km buffers) surrounding protected habitats
(i.e. designated haul outs and Special Areas of Conservation (SACs)) on the west
coast of Scotland was also assessed.
3. All tagged seals and waters surrounding 51 of 56 protected sites were predicted
to be exposed to ADD noise exceeding median ambient sound levels. Temporary
auditory impairment was predicted to occur in one of the seven tagged harbour
seals and across 1.7% of waters surrounding protected habitats over a 24-hour
period, when assuming a 100% ADD duty cycle.
4. Although the predicted risk of auditory impairment appears to be relatively low,
these findings suggest that harbour seals inhabiting inshore waters off western
Scotland are routinely exposed to ADD noise that exceeds median ambient sound
levels. This chronic exposure risks negative consequences for individual harbour
seals among the wider population in this region. The use of ADDs to mitigate
pinniped depredation should be carefully considered to reduce unintended
habitat-wide impacts on non-target species, including pinnipeds that are not
specifically interacting with aquaculture.
Description
Keywords
acoustic deterrent device (ADD), aquaculture, depredation, harbour seals, marine protected areas, noise pollution, pinnipeds