By Vince den Hertog, P. Eng. and Andra Papuc, P. Eng.
To marine life, the world beneath the waves is more one of sound than of light.
For many sea creatures, their ability to communicate, eat, reproduce, and navigate can depend on how well they can propagate and hear sound underwater.
Noise pollution can interfere with behaviors that depend on sound for the smallest fish to the largest whales. In the Salish Sea alone, there are 3000 species of macro invertebrates, over 250 species of fish, and 37 mammal species sharing the waters.
Which sound frequencies are important and how different aquatic animals respond to them varies enormously, and it is not always known for a given species. Depending on their sensitivity and how close, powerful, and sustained the source of anthropogenic (human-made) sound is, impact can vary between behavioral changes, masking of communications, impairment of hearing, physical and physiological effects, and even death.
Whales are known to be highly reliant on an underwater environment free of interfering noise to communicate, navigate, and hunt. In the Salish Sea, there are three types of killer whales: the Resident killer whales, the Transient killer whales (or Bigg’s killer whales) and Offshore killer whales. Within the Resident killer whale population there are two communities: the Northern and Southern residents. The Southern Resident Killer Whales (SRKW) were listed as Endangered under the Canadian Species at Risk Act in 2003. Today, the number of SRKW is almost as low as the lowest observed count recorded in 1973. The pressure on the population has been linked to the decline of Chinook salmon (which make up about 80 per cent of their summer diet) chemical contaminants, disturbances from shipping and boat traffic, and high background underwater noise levels impacting communications and hunting.
The Underwater Radiated Noise (URN) characteristics from marine vessels and its impact on the marine environment is deservedly getting more attention than ever before from environmental organizations, government, industry, and the public. This is so not only for the Salish Sea but also for other areas of the world where whales and marine traffic end up in proximity. In major ports, the growing awareness of URN impact to whales and other sea life has seen incentive-based initiatives and new regulations. Here in B.C., the Port of Vancouver ECHO program is working to understand impacts to at-risk whales and promote noise reduction measures such as vessel slowdown. The Port of Prince Rupert also has an underwater noise monitoring and reduction incentive program. Transport Canada has been supporting research into human-caused noise from shipping mainly from propeller cavitation and onboard machinery.
Recently, Robert Allan Ltd. completed a project with financial assistance provided under the Innovative Solutions Canada program administered by Transport Canada on behalf of Innovation, Science and Economic Development Canada (ISED), to reduce URN generated by tugs that escort large commercial vessels through the critical habitat of the SRKW in the Salish Sea. In the first phase, Robert Allan Ltd., working with noise experts from the University of British Columbia, Memorial University, and Dalhousie University, developed a parametric tool for estimating URN characteristics of tugs equipped with azimuthing stern drives so that predictions can be made about how choices in propellers and propulsion equipment made at a tug’s design stage will translate into actual underwater noise and SRKW impact once a tug is in service.
Building on an existing Robert Allan Ltd. tool for predicting atmospheric emissions called RAptures, a new URN module has been added called TugEm designed not only to predict escort tug noise, but also to assess the relative impact of noise and mitigation measures on SRKW in terms of probability of detection, communication range, echolocation range, and sound exposure level. The proof-of-concept version of TugEm was calibrated using a rich set of measured noise data collected through the Port of Vancouver ECHO program initiative in the Salish Sea and was used to demonstrate how low-noise propeller and machinery installation choices can meaningfully reduce the impact on the SRKW.
In the next phase of development, the plan is to validate TugEm URN predictions from new underwater noise measurements made with a dedicated hydrophone listening station. Data will be collected systematically with several escort tugs operating under different speed and power conditions including on arrival here in B.C. our ElectRA series battery powered tugs currently under construction. The sophistication on the underlying models used within TugEm to predict cavitation, propeller noise, structure-born noise, and the effectiveness of machinery isolation will be increased to improve prediction accuracy.
With the refinements planned, TugEm will become a powerful and versatile tool to evaluate the URN reductions possible from best available current and future URN reduction technologies, including quiet propeller designs and battery electric propulsion. Making escort tugs as quiet as possible is one of many measures that will help improve the underwater environment for the resident killer whales and our other underwater neighbors in the Salish Sea.