A localized anomaly like that happened in 2009, causing an above-average number of strandings.
"The prevailing onshore winds did not blow as strongly as they usually do and it resulted in a lack of upwelling, which created a foraging difficulty for California sea lions," Wilkin explained.
Toxic algae blooms and infectious disease outbreaks also can trigger mass pup strandings. Researchers don't have evidence that either of those factors are contributing to the problem this year, but scientists are still waiting to see if tests on blood and tissue samples turn up bacterial, viral and other infectious agents or radioactive traces.
In a good sign, there has been a slowdown in the number of stranded, starving sea lion pups being admitted to rehab facilities, Wilkin said. At the same time, other animals are washing up. Northern elephant seals have just entered their stranding season and biologists have found a few adult female sea lions suffering from seizures, suggesting they may have been poisoned by the neurotoxin domoic acid, which is produced by multiple species of the genus Pseudo-nitzschia, a type of algae.