SMRU Consulting scientist Jason Wood had a paper published this week on shipping noise, which at close range has high frequency components that could have the potential to mask endangered Southern Resident killer whale calls or echolocation clicks.
Commercial ships ply the world’s oceans on a daily basis as they move raw materials and consumables around the world. Since the 2nd World War the global commercial shipping fleet has grown substantially resulting in an increase in low frequency noise in the world’s oceans. The noise produced by commercial shipping is the dominant source of underwater noise at frequencies <200 Hz. Increasing noise levels within the oceans are of particular concern for marine mammals as they rely on sound to communicate, hunt, detect predators and find mates.
Baleen whales are known to be more sensitive to low-frequency underwater noise often associated with shipping, displaying both behavioral and physiological responses to ship noise. This is because they are low-frequency specialists with hearing thought to be most sensitive at frequencies of 10-1000 Hz. Less is known about the potential effects of shipping noise on toothed whales whose hearing sensitivities range from 150 Hz-160 kHz for mid-frequency cetaceans and 200 Hz-180 kHz for high frequency cetaceans.
The inland waters of southern British Columbia and northern Washington State are an ideal place to study ship noise in a coastal environment as the waters are transected by major shipping lanes taking vessels to and from the ports of Vancouver, British Columbia, and Seattle and Tacoma in Washington State. During the summer these waters are also the core habitat of the endangered Southern Resident killer whales (SRKW), whose population currently numbers 85 whales.
In a study, published this week a team of scientists including Jason Wood, Operations Manager and Senior Scientist for SMRU Consulting North America, set out to measure the noise levels of different types of ships that are commonly encountered within the shipping lanes.
Jason and his colleagues measured the underwater noise from 1,582 unique ships that made 2,809 northbound transits through Haro Strait from March 2011 to October 2013. They classified ships into 12 different categories that encompassed bulk carriers, container ships, tug boats, cargo ships, vehicle carriers, tankers, military vessels, fishing boats, passenger vessels, pleasure craft and research vessels. Over half the recorded shipping traffic were bulk carriers and container ships. While container ships were some of the loudest of all vessel types recorded, military vessels were found to be the quietest.
The study found that shipping within this coastal area causes significant underwater noise at both low- and high-frequencies, well within the ranges (10 kHz-40 kHz) that killer whales use to communicate, hunt and navigate. This means that at close range shipping traffic may have the potential to mask the calls or echolocation clicks by killer whales.
While this study highlights the implications of shipping noise on one population of killer whales it is not unreasonable to assume that other mid- and high-frequency cetaceans could also be affected. In the mean time, ships may be able to reduce the noise emitted into the marine environment by reducing their speed and so reduce their impact on the wider marine environment.
Here is some news coverage for this paper:
- The Guardian
- The Vancouver Sun
- The Sidney Morning Herald
- The Washington Post
- The Christian Science Monitor
Here are some other examples of our work involving Southern Resident Killer Whales: