Far‐reaching effects of a seal scarer on harbour porpoises, Phocoena phocoena

Abstract

ABSTRACT1. Although seal scarers are widely used both to reduce economic losses at fish farms caused by seal predation and to reduce risks posed to marine mammals by offshore pile driving activities, the spatial extent of their deterrent effect on harbour porpoises is still largely unclear. However, this information is crucial to understanding the effects these devices have on the marine environment and to judge their potential as a mitigation measure.2. A study was conducted in the German North Sea, using passive acoustic monitoring and to some extent simultaneous aerial surveying to specifically study the spatial extent of the deterrence effects of a seal scarer on harbour porpoises. In order to link porpoise detections at various distances to actual sound levels, sound measurements of the seal scarer signal were carried out at several distances from the source.3. C-POD recordings revealed a significant deterrence effect on harbour porpoises up to 7.5 km away (at about 113 dB re 1 mPa rms ), much further than previously reported. During seal scarer operation the number of porpoise detections within 750 m of the C-PODs decreased by between 52 and 95% of the value before the seal scarer was activated.4. An aerial survey revealed a significant decrease in porpoise density from 2.4 porpoises km -2 before to 0.3 porpoises km -2 during seal scarer operation within the 990 km 2 study area, showing that the decrease in porpoise detections by passive acoustic monitoring was probably indeed the result of a decrease in porpoise abundance. 5. These results may raise serious concerns about unwanted disturbance effects on harbour porpoises in the context of seal scarer use at fish farms and also highlight the need for caution when applied as a mitigation measure during offshore construction.

Bubble curtains attenuate noise from offshore wind farm construction and reduce temporary habitat loss for harbour porpoises

“…Seal scarers have been shown to effectively displace porpoises several kilometres (Brandt et al 2012(Brandt et al , 2013 and the cumulated noise exposure from pile-driving noise is therefore substantially reduced, minimizing the number of porpoises at risk of developing TTS. The results from DanTysk indicate that the seal scarer indeed deterred porpoises, up to a distance of at least 12 km and perhaps even 18 km from the pile driving, seen as a significant reduction in %PPM (Fig.…”

“…However, if time− area regulation is not feasible (steady or unpredictable presence of animals), animals can instead be deterred to distances where the risk of PTS/TTS is reduced to acceptable levels before commencing full-scale pile driving. This deterrence can be achieved using seal scarers, originally developed to keep seals away from aquaculture and fishing gear, but demonstrated to be even more efficient at deterring harbour porpoises (Johnston 2002, Brandt et al 2012. Also, a gradual increase in hammer impact energy and strike rate (a so-called ramp-up or soft start), as is often done in the beginning of pile driving for pure technical reasons anyway, may also be effective, as it allows porpoises to swim away while being exposed to lower noise levels than during full-energy impact piling.…”

Measuring responses of harbour seals to potential aversive acoustic mitigation signals using controlled exposure behavioural response studies

“…For example, Brandt, Höschle, Diederichs, Betke, Matuschek, Witte, et al (2013) and Brandt, Höschle, Deiderichs, Belke, Matuschek, et al (2013) investigated porpoise responses to a particular type of ADD (the Lofitech Seal Scarer; Lofitech, Leknes, Norway) to assess its efficacy as an aversive sound source for mitigating pile-driving risks for this species. If regulators are to rely on aversive signals to protect marine mammals from hearing damage, then robust evidence is required to show how effectively and reliably they can exclude animals from areas of risk.…”

Offshore Wind Energy: Good Practice in Impact Assessment, Mitigation and Compensation

“…Pile driving causes loud underwater noise, which can harm marine mammals, particularly harbour porpoises (BSH and BMU, 2014). Pingers/seal scarers are used to exclude porpoises from the areas around pile sites (Brandt et al, 2012). The pile driving must also begin at a low energy level and gradually increase.…”

“…The noise of pile driving also has a strong but temporary displacement effect on harbour porpoises. No long-term impacts on the numbers of porpoises around OWFs have been found some time after the ramming (Nehls and Betke, 2011;Scheidat et al, 2011;Brandt et al, 2012;Haelters et al, 2012;Wahl et al, 2013). During the operation of OWFs, the abundance of harbour porpoises was shown to be similar to or higher than that prior to the construction of the OWF (Scheidat et al, 2011(Scheidat et al, , 2012Dähne et al, 2014;Schuster et al, 2015).…”