Sea lions exhibiting seizures, confusion, and erratic behavior are increasingly washing up on California beaches, raising alarms among wildlife experts and prompting public warnings. The animals are suffering from brain damage caused by domoic acid, a neurotoxin that contaminates local fish populations. This toxin affects the parts of a sea lion's brain responsible for memory and behavior.
Wildlife officials have reported dozens of affected sea lions in late August and early September, a surge that has the Marine Mammal Center in the Bay Area urging the public to stay at least 150 feet away from any distressed animals. While there have been no reported attacks on humans this year, similar incidents in 2025 saw disoriented sea lions attacking people.
The increased number of cases this year, exceeding 100 so far compared to an average of 70 to 90, is concerning to experts, especially the late-season surge. Giancarlo Rulli, a spokesperson for the Marine Mammal Center, noted the unpredictable nature of these flare-ups, which have appeared, subsided, and reappeared. "The fact that we are about to turn the page on August into September and just the unknowns right now of how these flare-ups have kind of popped up, surged, dissipated, and then popped back up again is a real concern," Rulli stated.
Domoic acid originates from algae blooms, particularly an organism called Pseudo-nitzschia, which multiply in nutrient-rich waters. These blooms can be exacerbated by oceanographic conditions, including upwelling and warmer water temperatures associated with phenomena like El Niño. Michael Milstein, a spokesperson for the National Oceanic and Atmospheric Administration (NOAA), explained that the toxin can be present during both cold and warm water years due to upwelling processes.
This toxin accumulates in fish like sardines and anchovies, which are a primary food source for sea lions. While sea lions are not typically aggressive, the neurotoxin can induce aggressive behavior. Direct contact with an affected sea lion or touching one does not lead to human infection. The primary risk to humans comes from consuming contaminated shellfish or seafood, which can lead to amnesic shellfish poisoning (ASP). Cooking or freezing does not neutralize the toxin, and high doses can be fatal.
The current hotspots for affected sea lions have been observed around the Monterey Peninsula and the Central California Coast, including Monterey and Santa Cruz counties. The Marine Mammal Center's hotline has received hundreds of calls reporting distressed marine animals. If left untreated, domoic acid poisoning can lead to seizures and heart failure in marine mammals. The California coast's sea lion population has grown significantly, from approximately 1,500 in the 1920s to about 250,000 currently.
