Behavioral responses of Chinook salmon to shipping noise in Cowichan Bay, British Columbia

The increase in human-generated noise over the last 60 years has led to concerns regarding the impacts of shipping noise on marine species. Two important species in the northeast Pacific are declining, southern resident killer whales and their main prey, Chinook salmon. We know that killer whales change their behavior in the presence of ships, but no work has been done on salmon. Acoustic receivers and underwater hydrophones were deployed in Cowichan Bay, British Columbia, Canada, to understand potential changes in behavior as salmon encounter shipping noise. Depth and acceleration of adult Chinook salmon were monitored using acoustic tags and were modeled against environmental conditions (e.g., currents) to understand general movement and behavior. Underwater sound pressure levels were then added to the model to assess potential responses to ship noise. Over 3 years, 53 Chinook salmon were tagged, resulting in 167,628 individual detections. Detections revealed spatial and temporal patterns in habitat use and behavior prior to river entry and provided the first data on Chinook salmon responses to anthropogenic noise. These data provide novel insights into the behavior of adult Chinook salmon and crucial information on the impacts of anthropogenic noise on this key species.