Assessments of anthropogenic impacts on marine wildlife often concentrate on large-scale displacement. However, changes in the activity patterns of animals that do not flee could also affect their energy balance. Increasing boat traffic raises concerns for exposed marine mammals. Understanding risk perception is critical for effective mitigation and management, but it is hard to disentangle the effect of noise, physical presence of boats, and context. We used passive acoustic techniques to quantify how boat disturbance affected bottlenose dolphin foraging activity, and characterized the conditions influencing responses. To account for potential masking effects of boat noise on foraging vocalizations (buzzes), we developed a novel procedure to estimate the relationship between buzz detection probability and noise levels in particular 1/3 octave bands. Bayesian hierarchical modeling was then used to assess the effect of boat presence on buzz occurrence, as well as potential interactions with noise level, location, year, day, hour, dolphin group size, and boat type and number. Our results indicate that boat presence was associated with a short-term 49% reduction in foraging activity, but there was no relationship with noise level. Differences between sites and between years suggested a variable susceptibility depending on foraging conditions. This effect increased for increasing number of boats and depended on boat type. This is the first study conclusively showing that boat physical presence, and not just noise, plays a large role in disturbance.
This work received funding from the MASTS pooling initiative and their support is gratefully acknowledged (Scottish Funding Council, grant reference HR09011, and contributing institutions). We thank Moray Offshore Renewables Ltd., Beatrice Offshore Wind Ltd. and DECC for access to equipment and acoustic data collected for parallel studies in this area. We also thank Moray First Marine, Barbara Cheney, Rebecca Hewitt, Rachel Plunkett, Tessa Van Heumen and Ewan Edwards for helping deploy and recover devices, and Laura Ceyrac and James Robbins for collecting visual data. Finally, we thank John Harwood, Doug Gillespie, Gordon Hastie, Len Thomas, Kate Brookes, Marianne Marcoux, Luke Rendell, Thomas Cornulier, Olivia Harries and Anja Wittich for advice on study design and analysis. We also thank two anonymous reviewers for their useful comments.
- Bayesian hierarchical model
- Behavioral response
- Feeding buzz
- Noise masking
- Passive acoustic data
- Vessel traffic
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Acoustic and visual data of bottlenose dolphin (Tursiops spp.) foraging vocalizations, boat presence and noise levels in the Moray Firth in 2012-2013
Pirotta, E. (Contributor), Merchant, N. D. (Contributor), Thompson, P. (Contributor), Barton, T. R. (Contributor) & Lusseau, D. (Contributor), PANGAEA: Data Publisher for Earth & Environmental Science, 2015