Scientists say a mass poisoning event of the animals took place after an algal bloom in Pacific waters
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Southern California beachgoers have been warned to be wary around sea lions after a mass poisoning event has made some more aggressive and potentially dangerous to humans.
A Ventura County surfer, RJ LaMendola, said that a sea lion attacked him on Friday and described the animal as "feral, almost demonic."
In a Facebook post describing the incident, LaMendola wrote that he was surfing when a frightening sea lion attacked him and tried to rip him off his board.
The surfer wrote that the animal then attacked him as he paddled to shore, sinking its teeth into his left buttock through his wetsuit.
He eventually made it out of the water and recalled looking back to see the sea lion pacing the shoreline and watching him.
“It was super intense,” he told the LA Times, “unlike anything I’ve ever seen in all the years I’ve been in the water.”
LaMendola, who has been surfing the area since 2006, reported the encounter to the Channel Island Marine Wildlife Institute and learned that there had been a rash of incidents involving the animals in Santa Barbara and Ventura County.
The strange behavior is believed to be caused by poisoning from domoic acid. Harmful algal blooms produce acids and can contribute to seizures and other health issues in sea lions.
A sick sea lion sits on a California beach in 2024. An algal bloom producing domoic acid in March, 2025, caused at least 140 sea lions to fall ill
A sick sea lion sits on a California beach in 2024. An algal bloom producing domoic acid in March, 2025, caused at least 140 sea lions to fall ill
The algal blooms create a neurotoxin — the domoic acid — which then accumulates inside filter-feeding fish like anchovies and sardines. The fish are a primary food source for larger mammals like sea lions and dolphins.
Wildlife officials have advised beachgoers not to approach any sea lion they suspect of being sick, as it could lash out and bite.
Local officials are working to try to help the sea lions, according to the LA Times. As of Friday, at least 140 seal lions showing domoic acid poisoning had been transported to the Marine Mammal Care Center in San Pedro, according to Chief Executive John Warner.
Sea lions aren't the only marine animals affected by the poisoning; at least 50 dolphins have also been affected and found stranded on beaches. They unfortunately nearly always die from domoic acid poisoning, and typically must be euthanized.
Sea lions have a 50 to 65 percent survival rate if they're treated quickly.
In 2023, a similar poisoning event affected sea lions off the coast of California. More than 1,000 sea lions died as a result.
Warner told the LA Times that climate change, driven by human burning of fossil fuels, is making toxic algal blooms more intense. Warming global temperatures caused by climate change and the increasing acidity of the ocean caused by runoff from nitrates have reportedly made these blooms more severe.
For example, if it rains in LA County, the water can carry organic materials as it runs off to sea. Manure and fertilizer — not uncommon sights on farms and ranches — produce nitrate runoff. The nitrates feed the algae, which makes them stronger.
“I liken it to a bloom put on steroids from human-caused factors that make these blooms worse every time we see them,” Warner said.
He said that this year's bloom is already worse than the 2023 event, and he described that year's bloom as the "worst domoic acid bloom in recorded history in Southern California."
Domoic acid can accumulate in shellfish, like mussels and oysters, and can then lead to poisoning in humans via ingestion, according to the California Department of Public Health.
The best way to avoid eating contaminated shellfish is to follow local guidance regarding algal blooms and to eat seafood prepared in restaurants, as their supply typically comes from commercial harvesters.