The use of seal scarers as a protective mitigation measure can induce hearing impairment in harbour porpoises

Abstract

Acoustic deterrent devices (ADDs) are used to deter seals from aquacultures but exposure of harbour porpoises (Phocoena phocoena) occurs as a side-effect. At construction sites, by contrast, ADDs are used to deter harbour porpoises from the zone in which pile driving noise can induce temporary threshold shifts (TTSs). ADDs emit such high pressure levels that there is concern that ADDs themselves may induce a TTS. A harbour porpoise in human care was exposed to an artificial ADD signal with a peak frequency of 14 kHz. A significant TTS was found, measured by auditory evoked potentials, with an onset of 142 dB re 1 μPa2s at 20 kHz and 147 dB re 1 μPa2s at 28 kHz. The authors therefore strongly recommend to gradually increase and down regulate source levels of ADDs to the desired deterrence range. However, further research is needed to develop a reliable relationship between received levels and deterrence.

Underwater Noise Emission Due to Offshore Pile Installation: A Review

“…In the United Kingdom, a separate environmental impact assessment (EIA) is followed per project in which acoustic deterrent devices (seal scarers) are used [60] together with trained marine mammal observers who monitor the activity using both visual inspection of the site and passive acoustic detection devices [61,62]. Similar regulations exist in several other countries and lessons learned from previously gathered experiences slowly find their way into new regulations [63,64]. The majority of the regulations though do not consider in detail the frequency content of the radiated noise; an item worth further investigation in the near future [65,66].…”

Auditory impairment from acoustic seal deterrents predicted for harbour porpoises in a marine protected area

“…Exposure to ADD noise has the potential to exceed levels estimated to cause temporary threshold shifts (TTS) in cetaceans (Schaffeld et al., 2019), and may induce behavioural changes, increasing the energetic demands on individuals (Mikkelsen et al., 2017). Additionally, ADDs can exclude animals from key habitats over long periods (Morton & Symonds, 2002).…”

A Result of Accidental Noise Pollution: Acoustic Flowmeters Emit 28 kHz Pulses That May Affect Harbor Porpoise Hearing

“…The study animal was a healthy adult female harbor porpoise born in 1995. The animal and the experimental setup were the same as in Schaffeld et al (2019). All trials were conducted adhering to the respective ethical principles as well as to the relevant international and national guidelines for animal experiments and under constant supervision of experienced biologists and animal trainers.…”

“…Hearing thresholds were determined by measuring auditory evoked potentials (AEPs) of the brainstem, a commonly used non-invasive electrophysiological technique (Nachtigall et al, 2016;Ruser et al, 2016;Schaffeld et al, 2019). AEPs were recorded by silver plated electrodes, gently attached to the body surface by suction cups, while the animals hearing was stimulated.…”

“…Biological consequences of noise exposure are reflected on multiple scales, reaching from displacement (Brandt et al, 2018), physiological stress (Rolland et al, 2012), disturbances in communication (Erbe et al, 2016;Kragh et al, 2019) or foraging (Wisniewska et al, 2018) up to hearing impairment (Reichmuth et al, 2019;Schaffeld et al, 2019). Anthropogenic noise is widely recognized as a pervasive and significant threat to wildlife (Francis and Barber, 2013), which can be particularly detrimental for vulnerable animals with high metabolic rates (Hoekendijk et al, 2018;Rojano-Doñate et al, 2018), like the harbor porpoise (Phocoena phocoena).…”