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An Annual Sea Lion Sickness Is Linked To Climate Change

The Marine Mammal Center
Chai, a male yearling California sea lion, rests lethargically near Pillar Point Harbor in San Mateo County before his rescue by trained volunteers from The Marine Mammal Center. He had domoic acid poisoning.


Since mid-May, disoriented and sometimes convulsing sea lions have been showing up on beaches across the Central Coast. It has become an annual occurrence with warming seas and algal blooms.

At The Marine Mammal Center is Sausalito, just north of San Francisco, year-round you’ll find a variety of marine mammals receiving treatment. And these days you’ll probably also find sea lions who are suffering from domoic acid poisoning, a condition that if left untreated, could cause permanent brain damage and death. 

The condition is most commonly caused by certain algal blooms, which produce a toxin known as domoic acid. Algae accumulates in fish that sea lions and other marine animals eat. The toxin then attacks their brains resulting in disorientation and seizures.  

“It is very common now for us to see a bloom of some sort every year, especially the last five or six years,” said Dr. Cara Field. She’s the medical director at The Marine Mammal Center. 

Credit Elena Graham - The Marine Mammal Center
Dr. Cara Field, pre-pandemic, listens to the lungs of a baby harbor seal during a check-up exam at The Marine Mammal Center's Sausalito hospital.

She says climate change and warming waters contribute to more algal blooms and consequently more sick sea lions. 

“That makes us very concerned that if we continue to see these unusual warm water events, we are going to end up with more and more algal blooms,” said Field. 

Over the last month or so, the center has seen well over 20 animals coming in with symptoms of domoic acid poisoning. Sick sea lions can sometimes weigh hundreds of pounds and require a team of people working together during a rescue. The coronavirus pandemic and the need for social distancing has slowed The Marine Mammal Center’s response time to these emergencies.  

Credit Bill Hunnewell - The Marine Mammal Center
The Marine Mammal Center's Medical Director Dr. Cara Field (left) examines a young California sea lion while it is carefully restrained by veterinary technicians pre-pandemic.

“We, like everybody else, are very concerned about human safety as well. There may be a delay of potentially hours before we're able to really fully respond and get an animal off the beach and on the way to the hospital,” said Field. 

The condition can have far reaching effects including on pregnant mothers and their pups as well. 

“That can cause developmental problems in the pup such that they may even be stillborn or the mother may abort early, or potentially if the pups survive that it often develops brain damage later in life,” said Field.

So if you see a sea lion in distress or acting oddly, Dr. Field advises the public to keep their distance and to call the Marine Mammal Center on 415-289-SEAL (7325). 


Credit Bill Hunnewell - The Marine Mammal Center
Chai, the California sea lion seen here exploring his pool pen during rehabilitation, is one of The Marine Mammal Center's success stories. He was recently released back into the wild after recovering from domoic acid poisoning.

“They are wildlife and as such are potentially dangerous. And they also need to rest. So it's really important that we give them their space,” said Field. 

Your presence could make the animals even more stressed. 

Treatment isn’t always possible. Sometimes the only answer is humane euthanasia and then an animal autopsy is conducted so scientists can try better understand this ailment. 

But there are many success stories like the sea lions recently rescued and currently being cared for at The Marine Mammal Center. The treatment they’re receiving will hopefully see them healthy and back in the wild very soon.


From 2019 to 2021 Michelle Loxton worked at KAZU as an All Things Considered host and reporter. During that time she reported on a variety of topics from the coronavirus pandemic, the opioid epidemic and local elections. Loxton was part of the news team that won a Regional Edward R. Murrow Award for the continued coverage of the four major wildfires that engulfed California’s Central Coast in 2020.