Dispersal, revisitation, and residency of satellite-tagged blue and fin whales in the Eastern North Pacific Ocean

We conducted a comparative analysis of movement strategies in blue (Balaenoptera musculus) and fin (B. physalus) whales across the eastern North Pacific (ENP). We assessed patterns of dispersal, revisitation, and residency within the California Current Ecosystem (CCE), a key seasonal feeding habitat, while considering biases in telemetry data such as device longevity, site fidelity, and sample representativeness. The dataset comprised 271 tracks from 176 blue and 95 fin whales tagged between 1994 and 2018 with two types of implantable tags. Tagging locations were grouped into southern California (SCA) and central-northern California (CCA–NCA) for blue whales, and SCA and central California-Pacific Northwest (CCA–PNW) for fin whales. Tag longevity differed strongly by species and device type. Blue whale tracks were generally longer, with over one-third of consolidated tags lasting > 91 d, while fin whale tracks were shorter and more constrained to early post-deployment. Both species exhibited strong site fidelity in SCA but expressed it differently: blue whales stayed longer per visit, while fin whales revisited more frequently. Blue whales dispersed farther from tagging sites and showed broader cohort-level spread, especially in CCA–NCA, while fin whales showed stronger residency in SCA. Seasonal shifts and interannual responses to ENSO and marine heatwaves were also evident. Contrasting movement strategies between blue and fin whales reflect ecological specialization and align with predictions from optimal foraging theory and niche partitioning. These patterns support mechanisms of coexistence through spatial and behavioral differentiation. Accounting for telemetry biases enhances ecological inference and supports range-wide assessments critical for conservation and management.