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Quieting the Waters

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File image courtesy Holly Fearnbach / NOAA

By Paul Benecki 2018-06-04 19:18:00

Orcas are charismatic, playful and well-publicized, and they might be British Columbia's best-known animals. One large subgroup is also endangered, and researchers say that ship noise - particularly cavitation - bears a large share of the blame.

Southern resident killer whales (SRKWs) are a genetically distinct population of orcas. In the summer, they congregate in the busy waters of the Strait of Juan de Fuca, Haro Strait and the Georgia Strait. Their population was reduced by collection for marine parks in the 1960s, and while they made a comeback in the 1980s, they have entered another period of decline. The total population is down to 76 individuals, including 30 breeding females.

Marine scientists say that the SRKW population is particularly stressed by ship noise. The whales hunt and communicate by hearing, and the background noise from marine traffic has grown so loud that they cannot forage as effectively as they have in years past. 

To address this problem, the Port of Vancouver recently underwrote a study on noise from passing vessels and potential abatement measures. With the participation of 52 vessel operators, the researchers used hydrophones to measure the noise generated by ships passing through Haro Strait at full speed and at 11 knots. Container ships were the loudest and showed the best potential for noise abatement through reduced speed, according to Krista Trounce, who ran the study for the Port of Vancouver. 

Consultants for the port found that shipowners can also reduce underwater noise pollution by taking a range of common energy efficiency measures, especially regular cleanings of their propellers and hulls. Equipment alterations also have an effect: efficiency devices like the Becker-Mewis duct and the propeller boss cap fin (PBCF) can cut down on fuel consumption, but they also reduce cavitation, which is by far the largest source of underwater noise.

Maersk has had considerable success with these interventions. Several years ago, Maersk Lines began an energy efficiency "radical retrofit" program for twelve neopanamax container ships. The alterations included a "nose job" - a replacement of the bulbous bow - a new propeller, a new propeller boss cap fin (PBCF) and other permanent alterations. These changes generated real fuel savings, with consumption down by 10 percent or more, according to Lee Kindberg, director of environment and sustainability for ‎Maersk Line North America. They also led to an unexpected reduction in underwater noise levels. 

"The sound pressure level, when corrected for vessel speed and draft, is now six decibels lower in the 8-100 hertz band and eight decibels in the 100-1000 hertz band," said Kindberg, speaking at the GreenTech 2018 conference. A three decibel reduction roughly equates to a 50 percent reduction in sound pressure levels. According to researchers at UCSD who helped Maersk analyze the ships' noise profiles, these reductions are significant enough to have an ocean-wide effect.  

Rising traffic volume

Any improvements aboard individual ships in the Georgia Strait will be at least partially offset by increasing traffic. A study completed for the Port of Vancouver in 2016 found that its successful container business will likely double by 2040, with the possibility of even faster growth. In addition, the Canadian government's purchase of the Trans Mountain pipeline means that a long-planned expansion will likely move forward, and crude tanker traffic will increase from four vessels per month to 34 - an increase in total marine traffic volume of about 14 percent. 

When it approved the the pipeline expansion, Canada's National Energy Board determined that it would have an effect on the SRKW orca population. "The board found that marine traffic in the Salish Sea is high and is increasing and, in fact, will increase regardless whether or not the project proceeds. And it found in the case of the southern resident killer whales, they are already impacted by the levels of traffic and any additional traffic that might be introduced by the Trans Mountain expansion project would likely be significant," said Dr. Robert Steedman, the board's chief environment officer.

The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.