The Perils of Underwater Noise

Dec 13, 2016

Ambient ocean noise is a natural part of the marine environment. This noise can come from waves cresting and crashing, the pitter-patter of rainfall, the strained moaning of sea-ice or an underwater rockslide. Ocean noise can also come from vessels, both large and small, and we are seeing an increase in vessel-related noise in B.C. waters.

Soundwaves travel by moving between particles that form an environment’s surroundings, such as air or water. Water – being approximately 800 times denser than air – has the ability to carry sounds great distances as particles are closer together and can therefore transfer energy, like soundwaves, with greater ease.

Cetaceans smartly take advantage of this phenomenon. It allows toothed cetaceans (odontocetes) to use vocalizations and echolocation – a bio sonar where they emit sounds into the environment and listen to the echoes returning off different objects – to navigate through expansive oceans, communicate with others, and forage for a meal. Baleen whales (myticetes) also use vocalizations for communication, an example being the remarkable low frequency “whale songs” often exhibited by humpback whales during their breeding season.

Underwater noise has been increasing since the start of the industrial revolution. Whether from seismic surveys or boat noise, human activities have gradually increased the amount of anthropogenic noise in the ocean. All ships create mechanical noise, which travels great distances, to the point where high-traffic areas have a constant baseline level of anthropogenic noise even when there is no ship nearby. It is thought that this ocean noise can disorient cetaceans and impede their ability to navigate, forage, or communicate. Underwater noise pollution can also increase the occurrence of vessel-cetacean collisions, as confused cetaceans may fail to recognize large vessels as threats.

Many natural cetacean behaviours may be disrupted by noise pollution, including foraging, diving, breeding, or vocalizing, resulting in long-term negative effects. Belugas, for example, will halt feeding activities and flee their productive grounds when an ice breaker is in the area, as highlighted in a 1999 study by Fisheries and Ocean Canada. In extreme cases, sources of great underwater noise such as military sonar have been linked to mass stranding events that may have resulted from acoustic trauma to nearby cetaceans.

There are, however, relatively simple ways much of this noise can be muted, if not eliminated altogether. While mechanical and structural retrofits to vessels can help reduce underwater noise, even simpler steps can be taken, such as transiting more slowly in known areas of cetacean-use and abiding by the Be Whale Wise Guidelines.

The B.C. Cetacean Sightings Network aims to better understand the occurrence and distribution of cetaceans along the B.C. coast, the threats they face, and how those threats can be mitigated. The Sightings Network uses their opportunistically collected data to identify cetacean hotspots,  areas where it’s important for vessels to take extra caution when transiting through.

The Sightings Network’s newly released Mariner’s Guide, a collaboration with the Port of Vancouver and the Prince Rupert Port Authority, provides a great source of information to large vessel crew with the goal of mitigating vessel-related threats to cetaceans such as noise pollution.

While there appears to be no imminent decline to vessel traffic, awareness of the issue is on the rise. There is still time to moderate this stress, this ironic symphony that many cetaceans endure, and help reduce threats in the years to come.

You can learn more about sound and noise in the ocean, its sources, as well as impacts to marine life here.

 

REFERENCES

Erbe, C. and Farmer, D.M. (2000) “Zones of impact around icebreakers affecting beluga whales in the Beaufort Sea” Acoust. Soc. Am. 129, 642–651.

National Research Council. (2005), “Marine Mammal Populations and Ocean Noise: Determining when noise causes biologically significant effects.” National Academies Press, Washington, D.C.

Rex K. Andrew, Bruce M. Howe, James A. Mercer. (2011) “Long-time trends in ship traffic noise for four sites off the North American West Coast”. J Acoust Soc Am.129(2): 642–651.

 

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