Hemisphere-Level Comparison of Climate-Driven Humpback Whale Breeding Migrations to the Eastern Pacific Off Costa...

This study evaluated humpback whale (Megaptera novaeangliae) occurrence off the Pacific coast of Costa Rica from 2001 to 2023, focusing on two Distinct Population Segments (DPSs), the Central America DPS and the Southeast Pacific DPS, which migrate from feeding grounds in opposite hemispheres. Using long-term sightings and Bayesian time-series and habitat models, we quantified the influence of absolute dynamic topography, sea surface temperature, and chlorophyll-a on whale occurrence, and assessed whether environmental conditions increased the likelihood of convergence between the two DPSs. Extreme environmental conditions, including El Niño events and marine heatwaves, negatively affected whale counts, particularly for the Central America DPS, and a sustained decline occurred from 2007 to 2019 followed by recent recovery. Seasonal and interannual patterns indicated a potential temporal overlap of both DPSs between October and November, with anomalous warming in the Northern Hemisphere increasing the probability of overlap. These results demonstrate climate-driven shifts in migratory patterns and connectivity, underscoring the need for continuous monitoring and improved tracking of both DPSs to inform conservation planning, whale-watching management, and the protection of critical breeding habitats.