Spatiotemporal patterns in the natural and anthropogenic additions to the soundscape in parts of the Salish Sea, British Columbia, 2018-2020

Anchored bulk carriers have substantial impacts on the underwater soundscape in Cowichan Bay, British Columbia

In recent decades shipping traffic has increased, leading to elevated underwater ambient noise levels. Research has been conducted on the noise generated by ships underway, however little is known about potential noise from ships at anchor. In coastal regions, commercial vessels can seek anchorages prior to entering port, leading to concern regarding the impacts on the soundscape and marine ecosystems. Cowichan Bay, British Columbia, a coastal region (800 Ha) 70 km away from the Port of Vancouver, was examined as a case study to understand the possible soundscape contribution from anchored bulk carriers. When a carrier anchored, sound pressure levels (SPL: 20-24,000 Hz) were elevated 2-8 dB re: 1 μPa throughout the bay. These results demonstrate the change anchored carriers can have on underwater soundscapes and is an important step in understanding the potential impact these vessels may have on marine organisms and important ecosystems.

Variability in Anthropogenic Underwater Noise Due to Bathymetry and Sound Speed Characteristics

Oceanic acoustic environments are dynamic, shaped by the spatiotemporal variability in transmission losses and sound propagation pathways of natural and human-derived noise sources. Here we used recordings of an experimental noise source combined with transmission loss modeling to investigate changes in the received levels of vessel noise over space and time as a result of natural water column variability. Recordings were made in the Juan de Fuca Strait, on the west coast of Vancouver Island, a biologically productive coastal region that hosts several cetacean species. Significant variability in noise levels was observed due to changing water masses, tied to seasonal temperature variation and, on a finer scale, tidal movements. Comparisons of interpreted received noise levels through the water column indicated that vessel noise recorded by bottom-stationed monitoring devices might not accurately represent those received by whales in near-surface waters. Vertical and temporal differences of 3–5 dB were commonly observed in both the recorded and modeled data. This has implications in estimating the success of noise mitigation measures, and our understanding of the change in sound fields experienced by target species for conservation.