Catastrophic and persistent loss of common murres after a marine heatwave

Recent marine heatwaves have had pervasive effects on marine ecosystems, from declines in primary production to die-offs of top predators. Seabird mortalities are often observed in association with heatwaves, but population impacts are not well understood. In this work, we report the rapid mortality of approximately half of Alaska's common murre (<i>Uria aalge</i>) population in response to an extreme marine heatwave. Between the 7-year period before (2008-2014) and after (2016-2022) the heatwave, murre numbers plummeted 52 to 78% at 13 colonies across two large marine ecosystems. We calculated a loss of 4.00 million common murres, the largest documented wildlife mortality event in the modern era. No evidence of recovery has yet been observed, suggesting that these ecosystems may no longer support historic numbers of seabird top predators.