Passive acoustic localization and tracking of Rice’s whales (Balaenoptera ricei) in the northeastern Gulf of Mexico

The endangered Rice’s whale (Balaenoptera ricei) is endemic to the Gulf of Mexico and is also the Gulf’s only resident baleen whale. Limited knowledge of this species’ ecology combined with the high industrialization of this region raises serious conservation concerns. As part of an ongoing project to study the Rice’s whale in its core habitat, an array of moored passive acoustic monitoring sites has been near-continuously deployed in the northeastern Gulf of Mexico since May 2021. While detecting Rice’s whale calls in these data provides valuable insight into the species’ spatiotemporal distribution, further analyses to localize and track individual whales would allow better characterization of their acoustic behavior and movement patterns, possibly allowing for density estimation. Here, we present a method for automated passive acoustic localization and tracking of calling Rice’s whales. The two key components of this approach are (1) the use of opportunistic sound sources to time-synchronize recordings across sites given clock-drift between acoustic recorders and (2) the implementation of automatic multi-target tracking techniques based on the Gaussian mixture probability hypothesis density filter. Analyses of the first four months of data show potential for measuring basic behavioral parameters such as calling rate, source level, and average swim speed.