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  • 1
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    Vessel noise effects on delphinid communication (2011)
    Inter-Research
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2009. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 395 (2009): 161-175, doi:10.3354/meps08204.
    Description: Increasing numbers and speeds of vessels in areas with populations of cetaceans may have the cumulative effect of reducing habitat quality by increasing the underwater noise level. Here, we first use digital acoustic tags to demonstrate that free-ranging delphinids in a coastal deep-water habitat are subjected to varying and occasionally intense levels of vessel noise. Vessel noise and sound propagation measurements from a shallow-water habitat are then used to model the potential impact of high sound levels from small vessels on delphinid communication in both shallow and deep habitats, with bottlenose dolphins Tursiops sp. and short-finned pilot whales Globicephala macrorhynchus as model organisms. We find that small vessels travelling at 5 knots in shallow water can reduce the communication range of bottlenose dolphins within 50 m by 26%. Pilot whales in a quieter deep-water habitat could suffer a reduction in their communication range of 58% caused by a vessel at similar range and speed. Increased cavitation noise at higher speeds drastically increases the impact on the communication range. Gear shifts generate high-level transient sounds (peak– peak source levels of up to 200 dB re 1 µPa) that may be audible over many kilometres and may disturb close-range animals. We conclude that noise from small vessels can significantly mask acoustically mediated communication in delphinids and contribute to the documented negative impacts on animal fitness.
    Description: This work was supported by the PhD School of Aquatic Sciences (SOAS), Aarhus University, DK, WWF Verdensnaturfonden and Aase & Ejnar Danielsens Foundation, the Siemens Foundation, a research agreement between La Laguna University and Woods Hole Oceanographic Institution, the Faculty of Science at the University of Aarhus, Denmark, and the Danish Natural Science Foundation via a Steno scholarship and frame grants to P.T.M. M.J. and N.A. were funded by the National Oceanographic Partnership Program.
    Keywords: Acoustic communication ; Vessel noise ; Masking ; Bottlenose dolphins ; Pilot whales ; Recreational vessels ; Whale watching
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    High source levels and small active space of high-pitched song in bowhead whales (Balaena mysticetus) (2013)
    Public Library of Science
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Public Library of Science, doi:10.1371/journal.pone.0052072.
    Description: The low-frequency, powerful vocalizations of blue and fin whales may potentially be detected by conspecifics across entire ocean basins. In contrast, humpback and bowhead whales produce equally powerful, but more complex broadband vocalizations composed of higher frequencies that suffer from higher attenuation. Here we evaluate the active space of high frequency song notes of bowhead whales (Balaena mysticetus) in Western Greenland using measurements of song source levels and ambient noise. Four independent, GPS-synchronized hydrophones were deployed through holes in the ice to localize vocalizing bowhead whales, estimate source levels and measure ambient noise. The song had a mean apparent source level of 185±2 dB rms re 1 µPa @ 1 m and a high mean centroid frequency of 444±48 Hz. Using measured ambient noise levels in the area and Arctic sound spreading models, the estimated active space of these song notes is between 40 and 130 km, an order of magnitude smaller than the estimated active space of low frequency blue and fin whale songs produced at similar source levels and for similar noise conditions. We propose that bowhead whales spatially compensate for their smaller communication range through mating aggregations that co-evolved with broadband song to form a complex and dynamic acoustically mediated sexual display.
    Description: This work was funded by the Oticon Foundation (grant # 08-3469 to Arctic Station, OT). OT and MC were additionally funded by AP Møller og Hustru Chastine Mc-Kinney Møllers Fond til almene Formaal, MS by a PhD scholarship from the Oticon Foundation, FHJ by a Danish Council for Independent Research, Natural Sciences post-doctoral grant, SEP by a grant from the U.S. Office of Naval Research, and PTM by frame grants from the Danish Natural Science Research Council.
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Estimated communication range and energetic cost of bottlenose dolphin whistles in a tropical habitat (2012)
    Acoustical Society of America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 131 (2012): 582-592, doi:10.1121/1.3662067.
    Description: Bottlenose dolphins (Tursiops sp.) depend on frequency-modulated whistles for many aspects of their social behavior, including group cohesion and recognition of familiar individuals. Vocalization amplitude and frequency influences communication range and may be shaped by many ecological and physiological factors including energetic costs. Here, a calibrated GPS-synchronized hydrophone array was used to record the whistles of bottlenose dolphins in a tropical shallow-water environment with high ambient noise levels. Acoustic localization techniques were used to estimate the source levels and energy content of individual whistles. Bottlenose dolphins produced whistles with mean source levels of 146.7±6.2 dB re. 1 μPa(RMS). These were lower than source levels estimated for a population inhabiting the quieter Moray Firth, indicating that dolphins do not necessarily compensate for the high noise levels found in noisy tropical habitats by increasing their source level. Combined with measured transmission loss and noise levels, these source levels provided estimated median communication ranges of 750 m and maximum communication ranges up to 5740 m. Whistles contained less than 17 mJ of acoustic energy, showing that the energetic cost of whistling is small compared to the high metabolic rate of these aquatic mammals, and unlikely to limit the vocal activity of toothed whales.
    Description: This study received support from the Danish Ph.D. School of Aquatic Sciences (SOAS), Aarhus University, DK, WWF Verdensnaturfonden and Aase & Ejnar Danielsens Foundation, the Siemens Foundation, the Faculty of Science at the University of Aarhus, DK, and the Danish Natural Science Foundation via a Steno scholarship and a logistics grant to PTM.
    Keywords: Acoustic arrays ; Acoustic noise ; Acoustic radiators ; Acoustic variables measurement ; Acoustic wave transmission ; Biocommunications ; Global Positioning System ; Hydrophones ; Underwater sound
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Clicking in shallow rivers : short-range echolocation of Irrawaddy and Ganges River dolphins in a shallow, acoustically complex habitat (2013)
    Public Library of Science
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS ONE 8 (2013): e59284, doi:10.1371/journal.pone.0059284.
    Description: Toothed whales (Cetacea, odontoceti) use biosonar to navigate their environment and to find and catch prey. All studied toothed whale species have evolved highly directional, high-amplitude ultrasonic clicks suited for long-range echolocation of prey in open water. Little is known about the biosonar signals of toothed whale species inhabiting freshwater habitats such as endangered river dolphins. To address the evolutionary pressures shaping the echolocation signal parameters of non-marine toothed whales, we investigated the biosonar source parameters of Ganges river dolphins (Platanista gangetica gangetica) and Irrawaddy dolphins (Orcaella brevirostris) within the river systems of the Sundarban mangrove forest. Both Ganges and Irrawaddy dolphins produced echolocation clicks with a high repetition rate and low source level compared to marine species. Irrawaddy dolphins, inhabiting coastal and riverine habitats, produced a mean source level of 195 dB (max 203 dB) re 1 µPapp whereas Ganges river dolphins, living exclusively upriver, produced a mean source level of 184 dB (max 191) re 1 µPapp. These source levels are 1–2 orders of magnitude lower than those of similar sized marine delphinids and may reflect an adaptation to a shallow, acoustically complex freshwater habitat with high reverberation and acoustic clutter. The centroid frequency of Ganges river dolphin clicks are an octave lower than predicted from scaling, but with an estimated beamwidth comparable to that of porpoises. The unique bony maxillary crests found in the Platanista forehead may help achieve a higher directionality than expected using clicks nearly an octave lower than similar sized odontocetes.
    Description: This study was made possible through the logistical and field support of the Bangladesh Cetacean Diversity Project of the Wildlife Conservation Society, and funded by frame grants from the Danish Natural Science Foundation to PTM. FHJ was supported by the PhD School of Aquatic Sciences, Denmark, and is currently funded by a postdoctoral fellowship from the Danish Council for Independent Research | Natural Sciences. VMJ was supported by a fellowship of the Wissenschaftskolleg Berlin. PTM was supported by frame grants from the Danish Natural Science Foundation.
    Repository Name: Woods Hole Open Access Server
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