Improving near real-time acoustic monitoring of two endangered whale species that make similar calls

Protecting marine mammals from anthropogenic threats, such as vessel strikes, requires accurate species occurrence data to ensure that management actions are justifiable. In Northwest Atlantic waters, several regions are seasonally monitored for baleen whales using near real-time (NRT) passive acoustic gliders. Two endangered species monitored, sei and blue whales, produce acoustically similar calls, complicating species discrimination in NRT. In this study, we sought to improve NRT blue whale monitoring in a region with irregular sei whale presence by implementing a new blue whale call library for automated detection and classification, and revised NRT analyst validation protocols. Acoustic detections from three deployments in 2025 were compared to six deployments from 2022-2024. NRT detections were reviewed audibly and visually to validate them post-deployment. The mean proportion of deployment days with detections misclassified as sei whale in NRT decreased from 3% to 0 in 2025, while true NRT blue whale detections increased by 89%. The new blue whale call library correctly classified blue whale calls in an average of 35% of blue whale ‘detected’ periods. Blue whale acoustic detections varied by season and location, with audible calls contributing to more detections than infrasonic calls. Overall, NRT misclassifications were reduced, and blue whale call discrimination improved, which is important for monitoring endangered species whose detection data inform conservation measures. These improvements are particularly relevant if either species is incorporated into future dynamic management strategies, such as the current NRT dynamic speed restriction program used to mitigate ship strike risk to North Atlantic right whales in the Gulf of St. Lawrence.