Marine heat wave off California linked to seabird deaths as El Niño forms

Marine ornithologist Tammy Russell found multiple seabird carcasses within minutes during a survey on a San Diego beach. Some carcasses were mixed with washed-up kelp; others lay under rocks. Each month, scientists and volunteers conduct surveys of dead seabirds along the California coast.

The surveys, run by various organizations for decades, establish baseline data used to detect changes in beached sea life.

Heat wave and food supply Many seabirds, including California brown pelicans, loons, and grebes, have starved in recent months. Record ocean temperatures have reduced the band of cold, nutrient-rich surface water where krill, anchovies, and sardines normally concentrate near shore, said Russell, a postdoctoral scholar at the University of California, San Diego, Scripps Institution of Oceanography.

Cormorants have been observed walking ashore and dying within an hour, Russell said. Similar observations have been reported along the entire coast.

El Niño outlook The National Oceanic and Atmospheric Administration confirmed in June that an El Niño has formed and is expected to strengthen. The event could extend into 2027 and further alter ocean temperatures and food availability. Scripps Institution of Oceanography recorded daily ocean temperatures at ten coastal stations.

Three stations broke records for 40 days or more this year, said program director Melissa Carter. Robotic underwater gliders also measured elevated temperatures offshore and at depth during spring. Dan Rudnick, who leads the Scripps glider program, said the warm anomaly off southern California this spring matched levels seen during the 2023 El Niño.