Blue whale song recorded by ocean bottom seismometers reveals distributions and behavior of late foraging season males in the northeast Pacific

Northeast Pacific (NEP) blue whales are one of the world’s most accessible and well-studied populations of blue whales. They are specialist krill feeders and have historically been described as capital breeders that feed off Southern California in the summer and breed in the Eastern Tropical Pacific in the winter. Recent studies have challenged this stereotypical characterization by describing large variations in NEP blue whale migration strategies. Our study investigates the behavior of whales that remain off the coast of the Pacific Northwest through the late winter by analyzing song produced by males. We acoustically localize B-calls recorded by a large opportunistic dataset of ocean bottom seismometers that were deployed offshore from Northern California through British Columbia in 2013-2014. We associate localizations into tracks that describe the movement of individual whales. We use tracks to analyze metrics of distribution, movement, and song and identify two distinct regions of different habitat use: the Gorda Basin as a migration corridor, and the Cascadia basin as a late-season foraging ground. We also leverage our ability to associate call metrics with whale movement to investigate links between song and other behaviors. We conclude that trends in song metrics including increases in call and phrase spacing may be driven by high energetic costs of repeating B-note production. We also suggest that different calls and phrase types may be used in different behavioral contexts including social functions associated with elements of foraging and migration.