Sea lions living off the coast of California have been acting strangely for some time. Some of them are displaying aggressive behaviour, while others appear lethargic. Marine researchers suspect that this is the impact of a toxic algae bloom in the area. The algae is believed to be releasing domoic acid, a neurotoxin which is entering the sea lions' bodies through the fish they consume.

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The toxins released by the algae can kill not only fish but also other mammals and birds. They can also prove harmful to humans, causing serious illness or death, according to the National Oceanic and Atmospheric Administration (NOAA).

According to the Marine Mammal Care Center, domoic acid can cause amnesic shellfish poisoning in humans and marine mammals. Jeni Smith, rescue supervisor at SeaWorld San Diego, told ABC San Diego affiliate KGTV that the sea lions appeared to be behaving in a strange manner.

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"Some animals seem very, very sleepy, maybe right after having a seizure," Smith said. "They may be abnormally aggressive."

Stargazing sea lion

One of the sea lions appeared to be stargazing, she said.

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Toxic algae blooms are typically seen only once every five to seven years. However, experts say that the warming climate and pollution have led to them blooming more frequently. 

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Dave Bader, chief operations and education officer at the Marine Mammal Care Center in San Pedro, told the channel that they have seen the blooms in Southern California for several consecutive years now.

Algae bloom in California can be deadlier this year

He added that the algae bloom this year is expected to be worse than the one seen in 2023. Since February, the centre has rescued nearly 150 sea lions, with dolphins and seabirds also reported to be falling sick from the toxins. According to the data from the Marine Mammal Care Center, the 2023 algae bloom killed 1,000 sea lions. 

ABC News quoted RJ LaMendola as saying that a "demonic" sea lion attacked him once while he was surfing at Oxnard State Beach in Ventura County, California. The sea lion bit him and dragged him, according to his Facebook post. He added that the sea lion was "feral" and "almost demonic."