Toxic ocean sends sea lions into frenzy; swimmers and surfers under threat

Along roughly 70 miles of Southern California’s coastline, an alarming number of sea lions are turning aggressive, leaving experts scrambling for answers as the typically friendly marine mammals bite swimmers and surfers. The underlying cause, scientists believe, is not malice—but poisoning from their own ocean habitat.

At the Marine Mammal Care Center in Los Angeles, staff are facing an unprecedented crisis. “The sea lions are coming in almost comatose by the time they’re stranding. Something is happening in this particular bloom that seems worse on multiple levels,” CEO John Warner told CNN.

“But volume-wise, it’s definitely the worst we’ve ever seen.”

Toxic algal blooms , commonly referred to as red tides , are likely behind the troubling behavior. These blooms produce domoic acid , a neurological toxin that makes its way up the food chain and into the diets of marine animals.

“When they are affected with this toxin, they’re out of their minds,” Warner explained CNN. “They’re scared. They’re totally disoriented and frightened. They really don’t understand where they are. They’re struggling to even get out of the water, so they don’t drown.”

The toxicity causes symptoms like breathing difficulty and seizures, including one known as "stargazing" in which sea lions unnaturally tilt their heads backward with closed eyes. In this state, the animals may act erratically, even aggressively. “If someone swims or walks next to them and they don’t see the animal or the animal doesn’t see them, that’s where some negative interactions can take place,” Warner warned.

One of the victims, 15-year-old Pheobe Beltran, was finishing a 1,000-yard swim during junior lifeguard tryouts in Long Beach on March 30 when she was suddenly bitten. “I was just so scared, so shocked, but I still felt the immense pain on my arms, like, over and over again,” Beltran said. Though her arms are bruised and scratched, she did not need stitches.

Another terrifying encounter took place days earlier in Ventura County, where surfer RJ LaMendola had a near-disastrous run-in near Oxnard. “The sea lion erupted from the water, hurtling toward me at top speed,” he wrote on social media. “Its expression was feral, almost demonic, devoid of the curiosity or playfulness I’d always associated with sea lions.” He described it as a “harrowing and traumatic experience” and said the animal even stalked him back to shore.

This year has been especially brutal for dolphins as well. “There’s no rehabilitation that’s going to work with dolphins,” Warner said. “Most of the time when they strand, they’re already deceased. The ones that are struggling on the beaches that are seizing... the best thing we can do is humanely euthanize them which, unfortunately, we’ve had to do more than we’ve ever done before.”

So far in 2024, the center has already treated 240 animals—just short of its annual budgeted capacity of 300. In addition to treatment, the budget must cover food, medicine, staff salaries, and even disposal of deceased animals. In just five weeks, the center has received over 2,000 emergency calls—far beyond the usual 3,000–4,000 seen annually.

Warner also noted that many of the affected animals are coming from the Channel Islands, which are the main breeding grounds for California sea lions . “This seems to be the epicenter of these domoic acid events the last four years,” he said. About 85% of California sea lions are born in that region every June.

Twenty dolphins have been found still alive after stranding this year, but many were already too ill to survive.

The increasing severity of these toxic events—and their deadly consequences—have experts deeply concerned, not just for marine life, but for beachgoers along California’s coast.