Mikkelsen, L., Hermannsen, L. & Tougaard, J. 2017. The effect of simulated seal scarer sounds on seals. Aarhus University, DCE – Danish Centre for Environment and Energy, 24 pp. Technical Report from DCE – Danish Centre for Environment and Energy No. 108. http://dce2.au.dk/pub/TR108.pdf
To test the effect of seal scarer noise on seals, we conducted an experimental study at the island of Anholt in Kattegat, Denmark, in September 2015. Seals were exposed to noise simulating that of a seal scarer, but with reduced source level. Reduced sound source level was chosen since experiments were placed inside the Natura 2000 site appointed to protect harbour and grey seals.
We show results from 13 conducted sound trials, where sound with a source level of 165 dB re 1µPa pp at 12 kHz were played in random intervals for 20 minutes. Baseline observations of seals were made at a minimum of 30 minutes prior to exposure trials and 40 minutes after the exposures. Sound exposures were conducted with a minimum of two hours interval between onset and no more than three sound exposures were made per day.
Observations/tracking of seals was achieved with a theodolite, a precision instrument for measuring angles in the horizontal and vertical planes. The theodolite can very precisely position an animal at sea and distances to the underwater loudspeaker can subsequently be calculated.
Results show that seals were observed at closer distances to the loudspeaker when sound was on compared to when sound was off. Significantly more seals were observed just after sound was played compared to just before. Hence, the reduced sound source appeared to attract the seals instead of deterring them.
