Normally, sea lions along the California coast are playful and can sometimes be heard barking like dogs. Recently, many have been found behaving strangely.
“The phone began ringing off the hook in late July 2024 for Channel Islands Marine & Wildlife Institute,” said the National Oceanic and Atmospheric Administration.
Andrew Leising, research scientist at NOAA Fisheries Southwest Fisheries Science Center, said a short-lived heat wave earlier this summer may have warmed coastal waters and set the stage for rapid algae growth at the root of the problem.
From July 29 through Aug. 7, the Marine Mammal Center in Sausalito responded to 90 mostly female sea lions affected by the domoic acid neurotoxin, according to NOAA. It said “nutrient-laden water from the deep ocean is driving a bloom of harmful algae,” that produces this neurotoxin.
“This is a toxin that is naturally occurring from an algae. It’s a microalgae – not the kind of like kelp you see on the beach,” explained Clarissa Anderson in an interview with Audacy’s KCBS Radio. She’s director of Southern California Coastal Ocean Observing System (SCCOOS) and the Cooperative Institute for Marine, Earth, and Atmospheric Systems (CIMEAS), operated out of UC San Diego’s Scripps Institution of Oceanography.
While Anderson said that this microalga blooms seasonally, scientists don’t know why or when it produces domoic acid. She said that its akin to an amino acid and that it interferes with glutamate receptors.
“You might think of the way we might react to Alzheimer’s or Parkinson’s disease,” Anderson said. “And so that is why the animals are reacting the way they are. When it gets into their system at a high concentration, it will have this neurological effect. You see the damage when you see the animals on the beach bobbing and weaving, foaming at the mouth, completely disoriented.”
Sea lions are especially vulnerable to the toxin because they are top predators and therefore feed on other animals exposed to domoic acid, such as anchovies and shellfish. This means that the toxin can build up in their bodies over time. NOAA Fisheries said domoic acid can cause seizures, brain damage and death.
“When you have these acute cases, a lot of the animals are unable to go back and they’re often euthanized, almost immediately because their symptoms are so bad,” said Anderson. She said most cases of sea lions stranded with domoic acid symptoms have been found near San Luis Obispo but that they’ve also been found further south near San Diego.
As marine mammals, sea lions are protected under the Marine Mammal Protection Act and their population has generally been increasing since protections began in 1975. However, the recent blooms have been an increasing threat.
“My understanding is that it is still going up. It started really at around mid-July [and] has been ticking up with every week,” Anderson said this week. Last year, a bloom impacted even more sea lions, leaving thousands stranded, she added.
While the neurotoxin does not appear to pose a risk to swimmers, NOAA said California beachgoers and their pets should stay a safe distance from sea lions that may be impacted by domoic acid. It also asked them to report strange sea lion beheavior to the West Coast Marine Mammal Stranding Network at (866) 767-6114.