Dozens of sea lions in California sick with domoic acid poisoning: Are humans at risk?

Dozens of marine mammals, including sea lions, dolphins and fur seals, have been found sick and disoriented in California the past month, according to local officials.

Responders with the Marine Mammal Center office in San Luis Obispo County have responded to approximately 90 sub-adult to adult California sea lions, three common dolphins and four northern fur seals "exhibiting symptoms consistent with domoic acid poisoning," since July 19, the center said in a statement Monday.

The symptoms include disorientation, lethargy and abnormal neurologic activity, such as twitching and seizures, the center said.

While cases were initially limited to the southern part of the county, especially in the Oceano Dunes and Pismo Beach areas in the first week of outbreak, but they have since then been reported in the north as well, including Morro Bay, Cayucos and Cambria.

"The intensity is currently at peak and it’s currently unknown how long the situation will last," the center said, adding their teams have "been actively coordinating responses" with California State Parks, especially in the Oceano area.

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Organizations in the West Coast Marine Mammal Stranding Network have been "getting upwards of 100 calls a day about sea lions that are appearing dazed and confused on the beach, and in some cases experiencing seizures and death," Michael Milstein, Senior Public Affairs Officer at National Oceanic and Atmospheric Administration, also called NOAA, told USA TODAY Monday.

Milstein said the organizations reported they are seeing affected animals mostly in Santa Barbara and San Luis Obispo Counties, "with some new indications that it is spreading south."

Why are sea lions and other marine animals getting sick in California?

High summer temperatures and an offshore marine heatwave in the Pacific that moved in close to the coast in July, followed by a cold anomaly may have prompted algal growth which produces a neurotoxin pseudo-nitzschia australis, which accumulates in prey species such as small fish, like sardines and anchovies, the Marine Mammal Center said. These are then eaten by sea lions in large quantities causing them to get sick.

Milstein explained the warming of coastal waters, followed by "a strong upwelling of deep, cold ocean water" kicked off the rapid growth of the algae.

"Sometimes these harmful algal blooms are tied to warm waters but in this case, the driver is strong upwelling of deep, cold waters, drawn to the surface by winds," Milstein said. "These waters are rich in nutrients, so they feed the algae."

A similar event occurred last year as well, the center said, adding the "large bloom event in southern California last year largely did not impact the central or northern California coast in terms of sick marine life but heavily impacted fellow West Coast Marine Mammal Stranding Network partners in southern California."

Hundreds of sick and dead sea lions and dolphins had washed up along Southern California beaches in the first few weeks of June last year, according to a statement by the NOAA Fisheries. High concentrations of domoic acid along Orange County and San Luis Obispo County was found, according to NOAA Fisheries, with the algae especially concentrated in the Santa Barbara Channel off the coast of Santa Barbara and Ventura counties.

Cases have previously surged past 200 in 2009, 2014 and 2015, "during large scale blooms that were also tied with El Niño patterns and warm water conditions off the Pacific West Coast," the center said.

June 2023:Toxic algae bloom suspected in deaths of sea lions and dolphins on Southern California coast

What happens in domoic acid poisoning?

Domoic acid attacks the brain and the heart causing seizures and heart failure and even permanant brain damage if left untreated.

While the toxin will naturally flush from an animal's system over time, sea lions and other marine mammals repeatedly exposed to the toxin will suffer longer-lasting and more serious effects, the center said.

"If these animals come into our care before significant damage occurs, we are often able to help flush the toxin from their systems by giving them fluids," the center said. The Marine Mammal Center is also the world’s largest marine mammal hospital and responds to an average of 60-80 sick sea lions per year.

The impacted sea lions are also fed domoic acid-free fish and are given anti-seizure medications used in humans, if they exhibit similar symptoms. The first case of domoic acid poisoning in marine mammals was diagnosed in 1998 and since then the center's veterinary team has been investigating new ways and therapies to reduce the amount of inflammation and damage the brain experiences while the animal is recovering.

Does domoic acid affect humans?

Domoic acid can also affect humans who eat contaminated crab, shellfish and fish, the center said, explaining that consumption can cause a life-threatening condition known as amnesiac shellfish poisoning. Since sea lions are often the first to be affected by a toxic algal bloom, the Marine Mammal Center said it provides public health department with information and data that can help determine if there is any threat to humans.

The California Department of Public Health, in an advisory on their website, has warned against eating sport-harvested mussels, clams, or scallops from Monterey, Santa Cruz, Marin, Sonoma, Humboldt or Del Norte counties due to dangerous levels of paralytic shellfish poisoning toxin.

The San Luis Obispo County Public Health Department addressed concerns surrounding the sick marine mammals Friday, informing the public that the ocean is currently safe for swimming and surfing. The department said the illness does not spread from animal to animal (including pets) or by swimming in the ocean.

Public advised to stay away from marine mammals

Experts at the Marine Mammal Center have urged the public to maintain distance from sea lions, whether they are impacted or not by the poisoning, due to their unpredictable nature and to avoid stressing out the animal, and to keep their pets away from them. Beachgoers and members of the public in San Luis Obispo County are also requested to report sick or injured marine mammals to the Center’s hotline at 415-289-SEAL (7325) so that trained responders can make an informed evaluation.

Beachgoers in Santa Barbara County can contact the Channel Islands Marine & Wildlife Institute at (805) 567-1505 to report a marine mammal in distress.

Saman Shafiq is a trending news reporter for USA TODAY. Reach her at sshafiq@gannett.com and follow her on X and Instagram @saman_shafiq7.