The targeted acoustic startle system (TASS) for marine renewable applications and construction sites
Marine renewable energy projects have the potential to come into conflict with conservation objectives during both, the construction (e.g. risk of hearing damage) and the operational phase (e.g. collision risk). With the growing renewable energy sector, there is a real need to mitigate this conflict. Conventional ADDs have been used to deter marine mammals in these scenarios but often operate at high duty cycle which causes unnecessary additional noise pollution. In addition, conventional ADDs do not always cause sufficient avoidance responses in seals (Mikkelsen et al., 2017) which may the result of habituation.
The ‘targeted acoustic startle system’ provides an alternative that can be used to induce a reliable induce avoidance response in the target species at a duty cycle (i.e. time during which sound is emitted) that is roughly one order of magnitude lower than in current commercial devices (Götz and Janik, 2015; Götz and Janik, 2016). If an animal enters the zone where received levels exceed the startle threshold the startle reflex will be triggered and the animal moves away from the installation. The animal can then be guided around the installation by repeatedly inducing avoidance responses each time the animal enters the zone where the received level exceeds the startle threshold. The source level of the unit can be flexibly adjusted to achieve the desirable deterrence ranges.
Species-specific differences in the hearing system of marine mammals can be exploited to achieve target-specific movement control by using startle signals that are centred within different frequency bands. The system has previously been shown to work for seals but ongoing research on harbour porpoise has shown promising preliminary results.
Götz, T. and Janik, V. M. (2015). Target-specific acoustic predator deterrence in the marine environment. Animal Conservation 18, 102-111.
Götz, T. and Janik, V. M. (2016). The startle reflex in acoustic deterrence: an approach with universal applicability? Animal Conservation 19, 225-226.
Mikkelsen, L., Hermannsen, L., Beedholm, K., Madsen, P. T. and Tougaard, J. (2017). Simulated seal scarer sounds scare porpoises, but not seals: species-specific responses to 12 kHz deterrence sounds. Royal Society Open Science 4.