Distribution and speed of recreational boats in Danish waters based on coastal observations and satellite images: Predicting where boats may affect harbour porpoises

Hao, Xiuqing; Nabe‐Nielsen, Jacob

doi:10.1016/j.ocecoaman.2023.106721

Cited by 2 publications

(3 citation statements)

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“…The widespread presence of recreational boats exposes cetaceans to high levels of disturbance. In Danish waters, where our study was conducted, recreational boats are often found in areas that are important harbour porpoise habitats (Hao & Nabe‐Nielsen, 2023 ). However, since the porpoises only appear to react to recreational vessels for a very short period when vessels are <200 m away, the population impact of this type of disturbances may be limited.…”

Section: Discussionmentioning

confidence: 99%

“…We did not observe obvious reactions from porpoises to the drone. Our selection of 10 and 20 knots as experimental speeds was based on the observed travelling speed for motorboats equipped with outboard engines (without sails) in Danish waters; 10 knots corresponds to mean travel speed while 20 knots corresponds to fast moving vessels (Hao & Nabe‐Nielsen, 2023 ).…”

Section: Methodsmentioning

confidence: 99%

“…However, studies investigating how animals react to recreational boats and how long their responses last are scarce. Considering the overlap of recreational boat traffic with harbour porpoise habitats (Hao & Nabe‐Nielsen, 2023 ) and the overlap between the frequency range of boat noise and porpoise hearing (Hermannsen et al., 2019 ), such knowledge is important for improving the conservation of porpoises and other cetaceans.…”

Section: Introductionmentioning

confidence: 99%

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Harbour porpoises respond to recreational boats by speeding up and moving away from the boat path

Hao,

Hamel,

Grandjean

et al. 2024

Ecology and Evolution

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Recreational boats are common in many coastal waters, yet their effects on cetaceans and other sensitive marine species remain poorly understood. To address this knowledge gap, we used drone video footage recorded from a recreational boat to quantify how harbour porpoises (Phocoena phocoena) responded to the boat approaching at different speeds (10 or 20 knots). Furthermore, we used a hydrophone to record boat noise levels at full bandwidth (0.1–150 kHz) and at the 1/3 octave 16 kHz frequency band for both experimental speeds. The experiments were carried out in shallow waters near Funen, Denmark (55.51° N, 10.79° E) between July and September 2022. Porpoises were more likely to move further away from the path of the boat when approached at 10 knots, but not when approached at 20 knots. In contrast, they swam faster when approached at 20 knots, but not when approached at 10 knots. The recorded received sound level did not depend on how fast the boat approached, suggesting that differences in porpoise responses were related to the speed of the approaching boat rather than to sound intensity. In addition, porpoises generally reacted within close proximity (<200 m) to the approaching boat and quickly (<50 s) resumed their natural behaviour once the boat had passed, indicating that the direct impact of small vessels on porpoise behaviour was most likely small. Nevertheless, repeated exposure to noise from small vessels may influence porpoises' activity or energy budget, and cause them to relocate from disturbed areas. The approach used in this study increases our understanding of recreational boats' impact on harbour porpoises and can be used to inform efficient mitigation measures to help focus conservation efforts.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%