Reduced survival of Steller sea lions in the Gulf of Alaska following marine heatwave

The North Pacific marine heatwave of 2014–2016 (PMH), one the most geographically-extensive and severe heatwaves on record, resulted in widespread persistent perturbation Gulf Alaska California Current ecosystems. Negative effects PMH mammals have been observed, but are not yet well understood. endangered Steller sea lion Eumetopias jubatus is an important top predator that also particularly vulnerable to sudden or ecosystem shifts. We examined survival 4,178 known-aged lions marked from 2000 2016 Kodiak Island through Southeast Alaska, using mark-recapture models 12,811 resightings collected 2001 2021. Survival adult females aged 3–15 was reduced -0.05 -0.23 during areas east, west, Cook Inlet. unaffected by PMH, Sugarloaf 5–8 -0.13 summer 2015 2016. Lowest occurred 2017, 2014 Reduced continued post-PMH Kenai Peninsula/Prince William Sound, Alaska. males insensitive except where male -0.25 2017. Prolonged intermittent high female mortality may reduce population growth initiate regional declines. response varied regionally despite similar patterns ocean warming throughout our study area, suggesting east versus west Inlet were affected differently perhaps due habitat oceanographic differences.