Measured variability of acoustic propagation loss in the Salish Sea, British Columbia, Canada

The Salish Sea encompasses the waters between southern British Columbia mainland coast, Vancouver Island, and Washington State. Its waters are used by commercial and recreational fishers, host shipping traffic to the major ports of Vancouver and Seattle, and is travelled frequently by local ferries. It is also an important habitat for many marine mammal species, including the endangered Southern Resident Killer Whale (Orcinus orca). Southern Resident Killer Whales use calls, whistles, and clicks to communicate and find prey. Human activities on the water may affect the marine acoustic environment by masking whale vocalizations, which in turn will negatively impact the ability of the whales to forage and socialize. A field study was conducted to measure acoustic transmission loss at various places in the Salish Sea. Sound signals simulating killer whale call elements were broadcast from different angles to a calibrated hydrophone. Results from the study showed that acoustic transmission loss is highly spatially variable in this area. We suggest that these observations are due to changes in oceanography conditions and ambient sound levels, which are important factors to consider when assessing impact on Southern Resident Killer Whales. [Work supported by the Oceans Protection Plan of the Government of Canada.]