Toxic Algae Outbreak Causes Surge in Sick Sea Lions Along California Coast

More than double the typical number of sick sea lions have washed ashore in California this year, stretching rescue teams to their limits as a toxic algae outbreak spreads along the West Coast.

At the Marine Mammal Center in Sausalito, workers have taken in more than 150 sea lions suffering from domoic acid poisoning since the start of the year. The naturally-occurring neurotoxin stems from harmful algal blooms, multiplying through the marine food chain as forage fish eat the algae and are then consumed by larger predators.

“It can cause lesions on the brain,” Giancarlo Rulli, who has worked at the Marine Mammal Center for 22 years, told CBS San Francisco.

Animals exposed to the poison experience lethargy, muscle twitching and severe seizures. Earlier this week, a sea lion found at Crissy Field in San Francisco died from exposure after rescuers observed the animal weaving and bobbing its head.

State agencies monitor animal strandings to help identify active algae blooms off the coast. Testing on local seafood continues year-round, with public health authorities increasing sample collection whenever risk factors rise. Officials warn that eating contaminated catches can cause severe illness or death in humans, urging people to check active fishery closures and safety advisories before eating local seafood.

Environmental scientists say climate conditions are driving the intensity of the current bloom. Dan Costa, a distinguished professor of ecology at UC Santa Cruz, studies sea lion movements to understand how ocean changes alter wildlife patterns.

“Because of the El Niño you have warming, which probably helps the harmful bloom,” Costa said. “And then that domoic acid gets released, fish eat it, and then it biomagnifies in the fish.”

Costa noted that warmer ocean temperatures are pushing sea lions farther north in search of food. “The conditions are more favorable up here for fish,” he said.

That shift leaves nursing pups vulnerable in traditional breeding grounds farther south. “You’ve got these poor little pups sitting on the beach starving to death,” Costa said.

Costa added that the crisis points to systemic issues beyond wildlife health. “The best thing we can do is to reduce human activities that put pollutants in the water,” Costa said.

The influx of distressed animals has created significant operational strain at treatment facilities. At the Sausalito call center, staff member Justin Hodges said daily report volumes had jumped sharply compared to last year.

“Last year was about 60 to 100 calls a day and now we’re looking at 300 to 600 calls per day,” Hodges said.

Rescuing a single adult animal often requires four to six people to safely transport the sea lion because they can weigh upwards of 300 pounds. It forces staff to triage incoming calls based on location, severity and available resources.

“It’s extremely labor intensive and physical,” Rulli said.

Veterinary teams treat patients using anti-seizure medication and fluids to help flush the toxin, though many animals arrive too ill to survive.

Despite the strain, rescue operations continued Thursday as teams returned three rehabilitated sea lions back to the wild.

“This work can be challenging yet incredibly rewarding,” Hodges said.

For responders, the broader trend remains a critical indicator of shifting ocean health.

“They’re telling a story,” Rulli said. "We’re in the midst of a severe outbreak of domoic acid poisoning. And how, in turn, that can also have implications for us as humans as well.”