The waters of West Hong Kong are home to a population of Indo-Pacific humpback dolphins (Sousa chinensis) that use a variety of sounds to communicate. This area is also dominated by intense vessel traffic that is believed to be behaviorally and acoustically disruptive to dolphins. While behavioral changes have been documented, acoustic disturbance has yet to be shown. We compared the relative sound contributions of various high-speed vessels to nearby ambient noise and dolphin social sounds. Ambient noise levels were also compared between areas of high and low traffic. We found large differences in sound pressure levels between high traffic and no traffic areas, suggesting that vessels are the main contributors to these discrepancies. Vessel sounds were well within the audible range of dolphins, with sounds from 315–45,000？Hz. Additionally, vessel sounds at distances ≥100？m exceeded those of dolphin sounds at closer distances. Our results reaffirm earlier studies that vessels have large sound contributions to dolphin habitats, and we suspect that they may be inducing masking effects of dolphin sounds at close distances. Further research on dolphin behavior and acoustics in relation to vessels is needed to clarify impacts. 1. Introduction Natural and anthropogenic sounds are part of the ocean environment. Natural sound is produced by physical (e.g., sea state, wind speed, precipitation, earthquakes) and biological (marine mammal vocalizations, fish communication, and snapping shrimp) sources ([1, 2] provide summaries). Anthropogenic sound, often termed “noise,” is caused by human activities such as explosives, seismic exploration, sonar, ships, industrial activities, and acoustic deterrent and harassment devices [1, 3]. Some of these noises affect marine mammal communication sounds, including Indo-Pacific humpback dolphins [4–7]. Additionally, short-term behavioral changes can occur in cetaceans due to noise (e.g., changes in surfacing, diving, and movement patterns [8–10]), but long-term or physiological impacts have been less well explored. Chronic sources of noise pollution have been hypothesized to contribute to population differences in the sound repertoire of various species, but this evidence is observational in nature and does not exclude intrinsic population differences, such as subspeciation [11–13]. Thus, a detailed investigation of the potential impacts of these local chronic noises may help to clarify the nature of population differences in marine mammal sounds and deepen our understanding of the potential effects of chronic noise exposure.
References
[1]
C. R. Greene Jr. and S. E. Moore, “Man made noise,” in Marine Mammals and Noise, W. J. Richardson, C. R. Greene Jr., C. I. Malme, and D. H. Thomson, Eds., chapter 6, Academic Press, San Diego, Calif, USA, 1995.
[2]
National Research Council, Ocean Noise and Marine Mammals, National Academy Press, Washington, DC, USA, 2003.
[3]
J. A. Hildebrand, “Anthropogenic and natural sources of ambient noise in the ocean,” Marine Ecology Progress Series, vol. 395, pp. 5–20, 2009.
[4]
M. M. Holt, D. P. Noren, V. Veirs, C. K. Emmons, and S. Veirs, “Speaking up: killer whales (Orcinus orca) increase their call amplitude in response to vessel noise,” Journal of the Acoustical Society of America, vol. 125, no. 1, pp. EL27–EL32, 2009.
[5]
M. L. Melcón, A. J. Cummins, S. M. Kerosky, L. K. Roche, S. M. Wiggins, and J. A. Hildebrand, “Blue whales respond to anthropogenic noise,” PLoS One, vol. 7, no. 2, article e32681, 2012.
[6]
K. C. Buckstaff, “Effects of watercraft noise on the acoustic behavior of bottlenose dolphins, Tursiops truncatus, in Sarasota bay, Florida,” Marine Mammal Science, vol. 20, no. 4, pp. 709–725, 2004.
[7]
S. M. van Parijs and P. J. Corkeron, “Boat traffic affects the acoustic behaviour of Pacific humpback dolphins, Sousa chinensis,” Journal of the Marine Biological Association of the United Kingdom, vol. 81, no. 3, pp. 533–538, 2001.
[8]
S. L. Ng and S. Leung, “Behavioral response of Indo-Pacific humpback dolphin (Sousa chinensis) to vessel traffic,” Marine Environmental Research, vol. 56, no. 5, pp. 555–567, 2003.
[9]
P. J. O. Miller, N. Biassoni, A. Samuels, and P. L. Tyack, “Whale songs lengthen in response to sonar,” Nature, vol. 405, no. 6789, p. 903, 2000.
[10]
S. M. Nowacek, R. S. Wells, and A. R. Solow, “Short-term effects of boat traffic on bottlenose dolphins, Tursiops truncatus, in Sarasota Bay, Florida,” Marine Mammal Science, vol. 17, no. 4, pp. 673–688, 2001.
[11]
T. Morisaka, M. Shinohara, F. Nakahara, and T. Akamatsu, “Effects of ambient noise on the whistles of Indo-Pacific bottlenose dolphin populations,” Journal of Mammalogy, vol. 86, no. 3, pp. 541–546, 2005.
[12]
P. Q. Sims, R. Vaughn, S. K. Hung, and B. Würsig, “Sounds of Indo-Pacific humpback dolphins (Sousa chinensis) in West Hong Kong: a preliminary description,” Journal of the Acoustical Society of America, vol. 131, no. 1, pp. EL48–EL53, 2012.
[13]
C. H. Frère, J. Seddon, C. Palmer, L. Porter, and G. J. Parra, “Multiple lines of evidence for an Australasian geographic boundary in the Indo-Pacific humpback dolphin (Sousa chinensis): population or species divergence?” Conservation Genetics, vol. 12, no. 6, pp. 1633–1638, 2011.
[14]
T. A. Jefferson, S. K. Hung, and B. Würsig, “Protecting small cetaceans from coastal development: impact assessment and mitigation experience in Hong Kong,” Marine Policy, vol. 33, no. 2, pp. 305–311, 2009.
[15]
B. Morton, “Protecting Hong Kong's marine biodiversity: present proposals, future challenges,” Environmental Conservation, vol. 23, no. 1, pp. 55–65, 1996.
[16]
T. A. Jefferson and S. K. Hung, “A review of the status of the Indo-Pacific humpback dolphin (Sousa chinensis) in Chinese waters,” Aquatic Mammals, vol. 30, no. 1, pp. 149–158, 2004.
[17]
C. L. H. Hung, R. K. F. Lau, J. C. W. Lam et al., “Risk assessment of trace elements in the stomach contents of Indo-Pacific Humpback Dolphins and Finless Porpoises in Hong Kong waters,” Chemosphere, vol. 66, no. 7, pp. 1175–1182, 2007.
[18]
B. Würsig, C. R. Greene Jr., and T. A. Jefferson, “Development of an air bubble curtain to reduce underwater noise of percussive piling,” Marine Environmental Research, vol. 49, no. 1, pp. 79–93, 2000.
[19]
B. Würsig and C. R. Greene, “Underwater sounds near a fuel receiving facility in western Hong Kong: relevance to dolphins,” Marine Environmental Research, vol. 54, no. 2, pp. 129–145, 2002.
[20]
S. K. Hung, “Monitoring of marine mammals in Hong Kong waters—data collection: final report (2011-12),” Tech. Rep., Agriculture, Fisheries and Conservation Department of Hong Kong SAR Government, 2012.
[21]
C. R. Greene Jr., “Acoustic concepts and terminology,” in Marine Mammals and Noise, W. J. Richardson, C. R. Greene Jr., C. I. Malme, and D. H. Thomson, Eds., chapter 2, pp. 15–32, Academic Press, San Diego, Calif, USA, 1995.
[22]
S. M. van Parijs and P. J. Corkeron, “Vocalizations and behaviour of Pacific humpback dolphins Sousa chinensis,” Ethology, vol. 107, no. 8, pp. 701–716, 2001.
[23]
S. Li, D. Wang, K. Wang, et al., “Evoked-potential audiogram of an Indo-Pacific humpback dolphin (Sousa chinensis),” The Journal of Experimental Biology, vol. 215, no. 17, pp. 3055–3063, 2012.
[24]
C. S. Johnson, “Sound detection thresholds in marine mammals,” in Marine Bio-Acoustics, W. N. Tavolga, Ed., pp. 247–260, Pergamon Press, Oxford, UK, 1967.
[25]
V. V. Popov, A. Ya. Supin, M. G. Pletenko, et al., “Audiogram variability in normal bottlenose dolphins (Tursiops truncatus),” Aquatic Mammals, vol. 33, no. 1, pp. 24–33, 2007.
[26]
R Development Core Team, R: A Language and Environment For Statistical Computing, R Foundation for Statistical Computing, Vienna, Austria, 2011, http://www.R-project.org/.
[27]
C. R. Greene Jr., “Ambient noise,” in Marine Mammals and Noise, W. J. Richardson, C. R. Greene Jr., C. I. Malme, and D. H. Thomson, Eds., chapter 5, pp. 87–100, Academic Press, San Diego, Calif, USA, 1995.
[28]
C. I. Malme, B. Beranek, and Newman, “Sound propagation,” in Marine Mammals and Noise, W. J. Richardson, C. R. Greene Jr., C. I. Malme, and D. H. Thomson, Eds., chapter 4, pp. 59–86, Academic Press, San Diego, Calif, USA, 1995.
[29]
S. Piwetz, S. Hung, J. Wang, D. Lundquist, and B. Würsig, “Influence of vessel traffic on movements of Indo-Pacific humpback dolphins (Sousa chinensis) off Lantau Island, Hong Kong,” Aquatic Mammals, vol. 38, no. 3, pp. 325–331, 2012.
[30]
R. Constantine, D. H. Brunton, and T. Dennis, “Dolphin-watching tour boats change bottlenose dolphin (Tursiops truncatus) behaviour,” Biological Conservation, vol. 117, no. 3, pp. 299–307, 2004.
[31]
D. Lusseau, “Male and female bottlenose dolphins Tursiops spp. have different strategies to avoid interactions with tour boats in Doubtful Sound, New Zealand,” Marine Ecology Progress Series, vol. 257, pp. 267–274, 2003.
[32]
L. J. May-Collado and D. Wartzok, “A comparison of bottlenose dolphin whistles in the atlantic ocean: factors promoting whistle variation,” Journal of Mammalogy, vol. 89, no. 5, pp. 1229–1240, 2008.
