Antarctic sea ice as a driver of humpback whale migration timing in the southeast Pacific

Understanding the drivers behind shifts in migration patterns is crucial for managing human activities that may affect whale populations and for assessing the ecological impacts of climate change on migratory species. This study investigates environmental factors influencing the migratory timing of humpback whales (Megaptera novaeangliae) in the Eastern Tropical Pacific (Breeding Stock G), using systematic shore-based observations from Ecuador between 2010 and 2023. We analyzed variables including Antarctic sea ice extent (SIE) and chlorophyll-a concentration (as a proxy for Antarctic krill density), the Oceanic Niño Index, Southern Annular Mode Index, and the Peruvian Coastal Thermal Index to assess their relationship with whale arrival dates and residency at the breeding grounds. Our findings show significant interannual variability in migration timing. For both with-calf and non-calf groups, SIE during the previous winter was positively correlated with arrival dates, onset of calving, and time spent at the breeding area. Broader sea ice extent likely enhances krill recruitment, increasing prey availability and allowing whales to build sufficient energy reserves to support longer stays at reproductive sites. This study highlights the potential negative effects of Antarctic sea ice loss on whale migration patterns. Krill fisheries should adopt precautionary strategies that account for year-to-year variability in prey availability to avoid disrupting whale foraging. Moving forward, it is vital to monitor these changes continuously and to evaluate their broader ecological consequences to ensure the long-term viability of migratory marine species in a changing climate.