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

Published source details Brandt M.J., Höschle C., Diederichs A., Betke K., Matuscheck R., Witte S. & Nehls G. (2013) Far-reaching effects of a seal scarer on harbour porpoises, Phocoena phocoena. Aquatic Conservation: Marine and Freshwater Ecosystems, 23, 222-232.
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This study is summarised as evidence for the following.

	Action	Category
	Use acoustic devices to deter marine and freshwater mammals from an area to reduce noise exposure Action Link

Use acoustic devices to deter marine and freshwater mammals from an area to reduce noise exposure

A controlled study in 2009 of a pelagic area in the North Sea, Germany (Brandt et al. 2013) found that deploying an active acoustic device reduced harbour porpoise Phocoena phocoena echolocation activity and sightings at distances up to 7.5 km from the device. The average percentage of minutes/h with porpoise activity was lower with the acoustic device turned on than turned off at distances of 0 m (0.1% vs 2.6% respectively), 750 m (0.6% vs 4%), 3 km (2.5% vs 10.2%) and 7.5 km (0.1% vs 3.1%) from the device. The difference was not significant at 1.5 km (1.1% vs 2.4%) or 5 km (0.8% vs 0.9%). Fewer porpoises were observed in the study area with the device turned on (average 0.3 porpoises/km²) than off (average 4 porpoises/km²). In July–November 2009, an acoustic device (Lofitech Seal Scarer) was tested by deploying it from an anchored boat 80 km offshore, 7–10 m below the water surface. The device was turned on (emitting 0.5 second pulses at a frequency of 14 kHz) for 10 x 4-h trials, each separated by at least four days with the device turned off (silent). Sixteen acoustic detectors arranged in a star pattern recorded porpoise echolocation clicks at distances of 0 m, 750 m, 1.5 km, 3 km, and 7.5 km from the acoustic device. Data were compared for 3 h before and 3 h during each of the 10 trials. On 10 August 2009, two observers recorded porpoise sightings along 30 aerial transects over a 990 km² area before and after the acoustic device was turned on.

(Summarised by: Anna Berthinussen)