Wildlife rescuers are reporting an increase in sick sea lions along California's central coast.
The culprit: domoic acid, a neurotoxin produced by harmful algal blooms.
The toxin accumulates in filter-feeding fish such as sardines and anchovies, which are consumed in large quantities by sea lions, dolphins and fur seals.
Giancarlo Rulli, spokesman for the Sausalito Marine Mammal Center, said that since mid-July, the center’s network has seen an increase in the number of affected sea lions along the coast in Santa Barbara and San Luis Obispo counties. He said rescuers have responded to more than 70 sea lions, as well as two dolphins and two fur seals.
Rulli said about 25 percent of those sea lions eventually died, either from disease or “humane euthanasia.” Dolphins and sea lions also died.
When staff reached the two dolphins, he said, they were convulsing on the beach.
“Once they’re out of the water, you’re in a race against time,” he said of the larger mammals. While sea lions typically spend time out of the water, if a dolphin stays on dry land for too long, its own weight will crush its organs.
Rulli said it is one of those tragic situations where “euthanasia is often the primary and number one response” to alleviate suffering, “especially when dolphins are having seizures.”
Staff at the Channel Islands Marine and Wildlife Institute have also received numerous calls about sick animals.
As of Friday, the institute was receiving about 100 reports a day of sick sea lions in Ventura and Santa Barbara counties. By Thursday, crews had saved 23 animals, said Samuel Dover, president of the wildlife rescue organization.
“Many more died,” he said.
Domoic acid attacks the brain and heart, causing seizures and heart failure. If left untreated, it often causes permanent brain damage. The toxin naturally clears the animal's system over time, but repeated exposure can cause longer-lasting and more severe effects.
Rulli said the behavior of an affected animal can be “varied: lethargy, disorientation, the classic head bobbing … the classic telltale signs that there is probably a neurological problem associated with domoic acid poisoning.”
Dover, of the Channel Islands Institute, said this year's algae bloom event is predominantly affecting adult female sea lions.
At similar events last year and in 2022, poisoning did not appear to discriminate by sex or age.
“But it's early days,” said Dover, who noted that while there were some reports as early as June, incidents of sick animals didn't really increase until late July.
He said the 2023 outbreak lasted 27 days, down from 37 in 2022.
Rulli said those outbreaks had occurred further south.
Rescuing the animals can be difficult, considering their size, she said. An adult female sea lion can weigh up to 250 pounds, and an adult male up to 1,000. She said it takes several people — four to six — to rescue an adult female, meaning resources are limited.
If the animal can be evaluated closely and stabilized, Rulli said, rescuers attempt to transport it to the institute's hospital in Sausalito.
Both Rulli and Dover warned people to give sick animals plenty of space on the beach.
The National Oceanic and Atmospheric Administration urges beachgoers to stay at least 50 yards, or about half a football field, away from seals and sea lions, whether the animals are sick or healthy, and to keep pets away.
Those who see marine animals they believe may be sick should call nearby wildlife rehabilitation experts, such as those at the Sausalito Marine Mammal Center, (415) 289-7325, or the Channel Islands Marine and Wildlife Institute, (805) 567-1505.
