Research Document 2021/058
Vessel presence and acoustic environment within Southern Resident Killer Whale (Orcinus orca) critical habitat in the Salish Sea and Swiftsure Bank area
By Vagle, S., Burnham, R., Thupaki, P., Konrad, C., Toews, S., Thornton, S.J.
Abstract
The soundscape of an area is defined by acoustic additions from natural and human-derived noise. Six moorings were deployed in the Salish Sea and the Swiftsure Bank area to describe the soundscape, and additions from abiotic and anthropogenic sources for May-October for 2018-2020. Commercial vessels transit international shipping lanes to ports including Victoria, Vancouver, Nanaimo, Port Angeles, Tacoma and Seattle through these waterways. In addition, the coastal cities are hubs for ferries, recreational, and whale watching vessels. The Salish Sea and the Swiftsure Bank area also contain protected critical habitat for Southern Resident Killer Whales (SRKW), including on La Perouse and Swiftsure Banks, and in Juan de Fuca Strait and Haro Strait.
Patterns in the soundscape through the summer were considered. The contributions from wind and rain were examined using data from the Environment and Climate Change Canada (ECCC) forecast model. Visualization of weather patterns showed considerable wind additions around Sooke in mid-summer, whereas offshore winds dominated in late-spring and early fall.
Vessel presence was quantified from Automatic Identification System (AIS) data. For the AIS non-mandatory smaller and recreational vessel types, aerial surveillance data were used to estimate presence. However, this was still considered to represent the minimum use of the study area by these vessel types. Acoustic metrics were also considered to track vessel presence.
To better appreciate the soundscape experienced by SRKW, the additions from natural and vessel noise in frequency ranges used for social communication (500 Hz to 15 kHz) and echolocation (15-100 kHz) were examined. This highlighted areas most impacted, and provided a means of evaluating relative quality of the acoustic environment within CH. Analysis of vessel presence and movements demonstrated the impacts of vessel presence.
A numerical vessel noise model was developed to allow for soundscape estimates in areas other than those monitored directly by passive acoustic recorders. Scenarios of forecasted changes in vessel presences in this area were also explored. A near-future expected increase in tanker traffic from approximately one weekly passage to one passage daily through the Salish Sea, corresponding to increases in shipping as a result of the Trans Mountain expansion project, was modelled.
Principal threats to survival and recovery of SRKW include physical and acoustic disturbance and vessel strike. Our analyses form the basis for discussions on acoustic disturbance and masking, resulting in reduced SRKW calling and echolocation extents.
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