William K Oestreich , Kelly J Benoit-Bird, Briana Abrahms, Tetyana Margolina, John E Joseph, Yanwu Zhang, Carlos Rueda, John P Ryan

In ecosystems influenced by strong seasonal variation in insolation, the fitness of diverse taxa depends on seasonal movements to track resources along latitudinal or elevational gradients. Deep pelagic ecosystems, where sunlight is extremely limited, represent Earth’s largest habitable space and yet ecosystem phenology and effective animal movement strategies in these systems are little understood. Analyzing seven years of continuous population-level passive acoustic observations, we find evidence for seasonal, latitudinal movements by sperm whales (Physeter macrocephalus) in the Northeast Pacific. Integration of population-level empirical results with individual-level movement simulations provides evidence of seasonal migration in this cryptic top predator, likely to track deep-sea resources. We show that sperm whales track oceanographic seasonality in a manner similar to many surface ocean predators, but with dampened seasonal-latitudinal movement patterns. These findings shed light on the drivers of sperm whales’ long-distance movements and the shrouded phenology of the deep-sea ecosystems in which they forage.