UC San Diego

Blue whale (Balaenoptera musculus) D calls are low-frequency vocalizations commonly produced during foraging, and although they are widely used in acoustic monitoring, the environmental factors that shape their detectability remain poorly quantified. Because blue whales are listed as an Endangered species, understanding how ocean variability affects the acoustic “visibility” of their calls is essential for accurate long-term monitoring and conservation efforts.Using the range-dependent parabolic-equation model RAMGeo, transmission loss was simulated at three monitoring sites spanning distinct bathymetric settings (submarine basin, shelf break, open ocean), and monthly detection areas were computed above five call received-level thresholds (80, 85, 90, 95, and 100 dB re 1 µPa) for the years 2007–2023.Detection areas covaried strongly with upper-ocean temperature and sound-speed gradients, with the largest acoustic footprints occurring during cooler, weakly stratified months and the smallest during warm anomalies, including major marine-heatwave periods. Sensitivity was strongest at mid-range thresholds (85–95 dB), whereas near-field detections above the 100 dB threshold were largely invariant across environments.Taken together, these results demonstrate that blue-whale acoustic detectability is strongly shaped by regional physical oceanography and bathymetric features, and highlight the importance of incorporating environmental context into passive-acoustic monitoring and interpretation of long-term trends for this endangered species.