Vacationers visiting Southern California beaches this July Fourth weekend are likely to encounter an alarming site: hundreds of sick sea lions recovering on the sand.
Federal and California scientists suspect that the stranding is the result of dangerous levels of a plankton-based toxin in the waters far offshore — which accumulate as a deadly neurotoxin in the bodies of apex predators, such as dolphins and sea lions.
So far, state and federal officials have counted more than 100 dead dolphins, and more than 500 sick and dying California sea lions, according to the National Oceanographic and Atmospheric Administration (NOAA).
“We just have a lot of animals coming ashore,” said Justin Viezbicke, the Marine Mammal Stranding Coordinator for NOAA.
“We have more than a hundred dolphins onshore — and most of those have come ashore dead,” Vizbecke said, noting that the dolphins that washed ashore alive had died soon after. He added that Southern California has also seen “hundreds of sea lions coming ashore.”
Sea lions are washing up dead too, he said — though the surviving ones are doing marginally better than the dolphins.
The stranding event is the most “severe in terms of environmental impacts over a geographic area” of the last 20 years, Clarissa Anderson of the Scripps Institute of Oceanography told reporters.
The number of washed-up animals has area rescue facilities in the greater Los Angeles area so overstretched that once their capacity is full, the recovering sea lions are “being left on the beach,” Viezbecke said.
“There’s unfortunately no other option given the current number of animals that are coming up,” he added.
With the holiday weekend coming up, local authorities have set up sea lion “rest areas” on the area’s beaches. The areas provide a space for the injured and ill animals to recover, but also serve as a way to protect beachgoers from any potential attack.
“With this neurotoxin, [sea lions] are not acting normally,” Viezbecke told reporters. “So we really want to try to avoid those human-animal interactions.”
Sick sea lions have bitten several surfers in Southern California in the past week, according to KTLA.
Scientists’ current theory — which they hope to confirm by early next week — is that the animals are being sickened by Domoic acid.
That toxin is the source of Amnesic Shellfish Poison (ASP) — which humans can catch from eating shellfish
The shellfish, however, are just a conduit. The toxin comes from their food: tiny Pseudo-nitzschia algae that brew it up within their tiny bodies — likely as a means of defense, according to a 2018 study.
That contamination gets more and more serious the larger a predator is, Anderson said.
“Small fish are feeding on [Pseudo-nitzschia], and those fish get fed upon by larger fish,” she explained. “And as you work your way up the food web to the top predators — marine mammals — you start to see this bio accumulation that leads to these top predators becoming the most sick.”
At the threshold sea lions are currently experiencing, Domoic acid “causes seizures, brain damage, and death in marine mammals,” according to a NOAA fact sheet.
The die-off gives a grim insight into the hidden world far off California’s coasts — suggesting that the mechanism causing stranding is more complex than scientists had thought, Anderson said.
Massive marine heat waves in 2015 and 2016 led to similar — though less severe — Domoic acid die off.
But scientists now believe that they had been missing a key piece: that hot temperatures had to combine with an upwelling of cold, nutrient-rich water from the deep ocean — the fertilizer that the heat-loving algae convert into a massive bloom.
Diatoms, she suggested, play a complex role in California’s coastal ecology.
“They’re part of what makes our ecosystem beautiful,” she said. “But they can turn toxic.”
Beachgoers who see distressed sea lions on the beach should give them space — not least because that can help the sick animals recover, Viezbecke said.
“These animals that are out on the beach, while they’re laying there, their bodies are actually over time working through this neurotoxin,” he continued. “Not all of the animals are going to get up and walk away from this — but some of those animals will have a much better chance if we give them space.”
If people stress out the sick animals, Viezbecke said, “it’s just gonna be harder recuperation time for them.”