Acoustic vector sensing reveals ecologically modulated sympatry of blue and fin whales

Earth’s largest animal species, blue and fin whales, share a similar life history strategy involving annual long-distance migration between foraging and breeding habitat. The difficulty of monitoring spatial distributions of both species simultaneously has limited understanding of their sympatry within foraging habitats that sustain them. In addressing this observational challenge, a valuable method is acoustic vector sensing of the sounds produced by the whales. Using three years of continuous acoustic vector sensor data, we examine habitat occupancy of blue and fin whales in the central California Current Ecosystem. While fin whales called almost exclusively from offshore deep-water habitat, blue whales called predominantly from shelf and slope water habitat—indicating an allopatric tendency. However, stronger sympatry occurred during the third year, as blue whales spent a greater proportion of time in offshore deep-water habitat. This year was distinguished by the strongest wind-driven coastal upwelling, the furthest offshore extension of upwelled waters, and the greatest abundances of krill that are prey of both whale species. upporting the recovery of endangered blue and fin whale populations requires understanding where and how they live, and acoustic vector sensing is effective for this purpose in ecological research and resource management.