Description
Danish coastal waters are a hotspot for recreational boating and harbour porpoises, but we have little knowledge about where porpoises are likely to be affected and how porpoises respond to boat noise. To gain knowledge on this, we 1) used satellite image to assess the spatial distribution of small boats in Danish waters, and investigated how the probability of observing boats was related to distance to the coast and number of people living nearby. 2) used drone videos to quantify how porpoises responded to an approaching motorboat at different speeds (10 and 20 knots). Our satellite image analysis showed that boats were more likely to occur at coastal and populated areas, and the probability of observing boats and porpoises in the same area was >10% in 3.0% of the study area. In addition, our experiments found that although porpoises responded differently to the boat approaching at different speeds, they moved further away from the boat path at both boat speeds. Importantly, the received boat sound level was the same for two speeds, suggesting that differences in porpoise responses were related to the boat speed rather than to sound itself. Porpoises resumed behaviour shortly after boat passages, implying the direct effects of boats was small. Nevertheless, repeated exposure to noise from small vessels could influence porpoises' foraging efforts and cause them to relocate from disturbed areas. Our study increases our understanding of recreational boats’ impact on harbour porpoises and can be used to inform efficient mitigation measures to help conservation efforts.| Period | 8 Mar 2024 |
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| Event title | Danish marine mammal symposium |
| Event type | Conference |
| Location | Lyngby, DenmarkShow on map |
| Degree of Recognition | National |