Science Advisory Report 2017/041
Evaluation of the Scientific Evidence to Inform the Probability of Effectiveness of Mitigation Measures in Reducing Shipping-Related Noise Levels Received by Southern Resident Killer Whales
- In Pacific Canadian waters, the Southern Resident Killer Whale (SRKW) population is listed as Endangered under the Species at Risk Act (SARA). Three key threats have been identified as contributing to their decline: availability and quality of prey, environmental contamination, and both physical and acoustic disturbance.
- The SARA requires identification of critical habitat (the habitat necessary for survival or recovery) for threatened or endangered species. An area of critical habitat for SRKW has been identified and is legally protected from destruction (Figure 1). Science Advice identifying additional critical habitat has also been developed.
- Sound is vital to whales (e.g., prey sounds, environmental sounds, echolocation and social calls) to carry out their life functions, including foraging, navigating and communicating, and these functions can be interfered with by ship noise as the spectral frequency ranges overlap.
- Vessel traffic is the largest source of underwater noise in the SRKW critical habitat, which is bisected by the primary shipping lanes for the Ports of Seattle and Vancouver. This review considered mitigation measures that could apply to commercial ships, but excludes vessels such as whale watching vessels.
- The purpose of this peer review process was to evaluate the scientific evidence related to mitigation measures that could be applied to reduce shipping-related noise within identified and proposed SRKW critical habitat. The process did not consider the habitat use by SRKW within those areas, or impacts of noise on the whales. Furthermore, feasibility, safety, and socio-economic factors were not considered in the review process.
- Noise emitted from ships varies with factors such as speed, loading, draft, engine type, etc. and can vary substantially between individual vessels.
- A small proportion of ships produce a disproportionately large amount of the total noise.
- Within a given location, the total vessel noise is a combination of the source level, the time the vessels spend in the area, and the local sound propagation characteristics.
- A range of mitigation measures were evaluated for the likelihood of reducing shipping related noise.
- Mitigation measures modify either the noise source (source-based) or the operation (operation-based) of the ship in space and time.
- Source-based mitigation measures (i.e., ship design and/or retrofit) have a global and long-term effect, and could be implemented incrementally as ships were modified or replaced. It does not require knowledge of whale presence, distribution or behaviour to be effective. In the long term, modification of ship design to reduce radiated noise is likely to have the greatest potential for improving the acoustic environment of SRKW.
- Operation-based mitigation measures (i.e., slowing down, relocation of traffic lanes, convoys) have the potential to reduce noise output and improve the acoustic environment of SRKW. These measures have a more local and temporary effect on the acoustic environment, and could be implemented simultaneously to multiple vessels. They also have more uncertainty in their effectiveness of mitigating noise impacts, because they require knowledge of whale presence, distribution, and behaviour.
- It is noted that some operation-based mitigation measures may have side-effects (e.g., redistributing noise into other habitats, or increasing duration of noise).
- The operation-based measures showing the most potential for improving the acoustic environment include reducing ship speed, transit time restrictions and convoying. Other measures that may have location- or spectral frequency- specific benefits include rerouting traffic and shifting traffic lanes.
- A combination of measures will likely be the most effective solution to improve the acoustic environment.
This Science Advisory Report is from the May 30 to June 1, 2017 National Peer Review Meeting on the “Evaluation of the Scientific Evidence to Inform the Probability of Effectiveness of Mitigation Measures in Reducing Shipping-Related Noise Levels Received by Southern Resident Killer Whales”. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.
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