%0 Journal Article
%T High-Speed Vessel Noises in West Hong Kong Waters and Their Contributions Relative to Indo-Pacific Humpback Dolphins (Sousa chinensis)
%A Paul Q. Sims
%A Samuel K. Hung
%A Bernd W¨¹rsig
%J Journal of Marine Biology
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/169103
%X 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¨C45,000£¿Hz. Additionally, vessel sounds at distances ¡Ý100£¿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¨C7]. Additionally, short-term behavioral changes can occur in cetaceans due to noise (e.g., changes in surfacing, diving, and movement patterns [8¨C10]), 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¨C13]. 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.
%U http://www.hindawi.com/journals/jmb/2012/169103/