1. Institute of Marine Research, Ecosystem Acoustics Group, Austevoll Research Station , Sauganeset 16, N-5392 Storebø , Norway
2. Operational Directorate Natural Environment, Royal Belgian Institute of Natural Sciences, 3e en 23e Linieregimentsplein , 8400 Oostende and Gulledelle 100, 1200 Brussels , Belgium
3. Institute of Marine Research, Ecosystem Acoustics Group , Nordnesgaten 50, 5005 Bergen , Norway
4. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Biology , Am Handelhafen 12, 27570 Bremerhaven , Germany