Mysticetes produce and use sound at the frequencies emitted by large ships, and they are considered to be more sensitive at these low frequencies than are other marine mammals (e.g., Parks et al., 2007b Cranford and Krysl, 2015). As ship noise peaks in the low frequencies, early studies primarily focused on low-frequency specialist species such as mysticetes (i.e., baleen whales) (e.g., Eberhardt and Evans, 1962 Cummings and Thompson, 1971). Ship traffic is responsible for the steady rise in ambient noise at low frequencies (10–100 Hz) in many ocean regions-a rate that has been reported to be as high as 3 dB/decade ( Andrew et al., 2002, 2011 Chapman and Price, 2011 Miksis-Olds et al., 2013 Miksis-Olds and Nichols, 2016).Ĭoncern about the potential effects of ship noise on marine mammals is not recent, but instead has been raised for decades (e.g., Payne and Webb, 1971 Myrberg, 1978 Geraci and St Aubin, 1980).

In fact, ships have become the most ubiquitous and pervasive source of anthropogenic noise in the oceans. Based on satellite altimetry, global ship density increased by a factor 4 between 19, with the greatest increase in the Indian Ocean ( Tournadre, 2014). Between World War II and 2008, the global number of ships rose by a factor 3.5 and the total gross tonnage by a factor 10 ( Frisk, 2012). Commercial ships are increasing in number as well as size, linked to overall economic growth ( United Nations Conference on Trade and Development, 2018). This includes watercraft ranging from small boats to large ships.

Marine traffic in the world’s oceans is increasing.

Moving forward, standards on study design, data analysis, and reporting are badly needed so that results are comparable (across space and time) and so that data can be synthesized to address the grand unknowns: the role of context and the consequences of chronic exposures. Last but not least, the biological significance of observed responses is mostly unknown. The lack of anthropogenic (e.g., different vessel types), environmental (e.g., different sea states or presence/absence of prey), and biological (e.g., different demographics) controls is a common problem, as is a lack of understanding what constitutes the ‘normal’ range of behaviors. We explain the fundamental concepts involved in the generation and propagation of vessel noise and point out common problems with both physics and biology: Recordings of ship noise might be affected by unidentified artifacts, and noise exposure can be both under- and over-estimated by tens of decibel if the local sound propagation conditions are not considered. Similarly, little is known about the potential effects of ship noise on pelagic and deep-diving marine mammals, even though ship noise is focused in a downward direction, reaching great depth at little acoustic loss and potentially coupling into sound propagation channels in which sound may transmit over long ranges. We identify knowledge gaps: There appears a bias to more easily accessible species (i.e., bottlenose dolphins and humpback whales), whereas there is a paucity of literature addressing vessel noise impacts on river dolphins, even though some of these species experience chronic noise from boats. The documented effects include behavioral and acoustic responses, auditory masking, and stress. We provide an overview of this literature, showing that studies have been patchy in terms of their coverage of species, habitats, vessel types, and types of impact investigated. Given the important role sound plays in the life functions of marine mammals, research on the potential effects of vessel noise has grown-in particular since the year 2000. A concomitant increase in underwater noise has been reported in several regions around the globe. The number of marine watercraft is on the rise-from private boats in coastal areas to commercial ships crossing oceans. 5School of Biological and Marine Sciences, University of Plymouth, Plymouth, United Kingdom.4Harry Butler Institute, Murdoch University, Perth, WA, Australia.3School of Environmental Sciences, Nelson Mandela University, Port Elizabeth, South Africa.2Institute of Marine Sciences, University of Portsmouth, Portsmouth, United Kingdom.1Centre for Marine Science and Technology, Curtin University, Perth, WA, Australia.

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