Range-Wide Comparison of Gray Whale Body Condition Reveals Contrasting Sub-Population Health Characteristics and Vulnerability to Environmental Change

Climate change is a global phenomenon, yet impacts on resource availability to predators may be spatially and temporally diverse asynchronous. As capital breeders, whales are dependent dense, predictable prey resources during foraging seasons. An Unusual Mortality Event (UME) of Eastern North Pacific (ENP) gray ( Eschrichtius robustus ) was declared in 2019 due dramatic rise stranded animals, many emaciated. have affected the primary grounds ENP (~20,000 individuals) Arctic sub-Arctic region coastal habitats between northern California, USA British Columbia, Canada where small sub-group called Coast Feeding Group (PCFG; ~230 forages. To investigate variability whale body condition relative changing ocean conditions, we compare two datasets aerial photogrammetry images collected via Unoccupied Aircraft Systems (UAS) wintering San Ignacio Lagoon, Mexico (SIL; n=111) PCFG feeding Oregon, (n=72) over same three-year period (2017–2019). We document concurrent improvement Oregon while SIL declined. This result indicates that UME reduced energetic gain some Arctic/sub-Arctic grounds, recovering from poor conditions NE marine heatwave event 2014–2016. Surprisingly, found had significantly worse than SIL, even when accounting for year phenology. derive support this unexpected finding analysis opportunistic (n=18) compared (n=30): lower (t=2.96, p=0.005), which cause reproductive capacity or resilience environmental perturbations whales. Overall, our study elucidates divergent across sub-groups time, demonstrate value UAS effectively monitor identify physiological response climate change.