Hundreds of sea lions die. Is an algal bloom to blame?

Call after call came in, with reports of sea lions waving their heads, foaming at the mouth or slumped lifeless on the beach. Rescue workers along California’s central coast struggled to catch the sick animals in hopes of rescuing them. Hundreds of sea lions and dozens of dolphins had already died.

The marine mammals — considered “sentinel” species because of what they tell humans about ocean health — are believed to be getting sick from a plague of harmful algae that occur naturally but can be exacerbated by human activity.

The algae, Pseudo-nitzschia, produces a neurotoxin called domoic acid that works its way up the food chain from anchovies to sea lions and dolphins, causing lethargy, disorientation, vomiting, bulging eyes, muscle spasms, seizures and, in severe cases, dead. The animals show up, sick and stranded, along the coastline from Santa Barbara to San Luis Obispo County.

Rescuers say it’s one of the worst mass poisonings they’ve ever seen. And it’s only June.

“It was really sad,” said Michelle Berman Kowalewski, a biologist and the director of the Channel Islands Cetacean Research Unit, a nonprofit organization that has responded to the stranded dolphins. Algal blooms are not uncommon, but Ms Berman Kowalewski said she could respond to 30 to 40 poisoned dolphins even in a bad year. “This year we have an average of 10 animals per day for 10 days,” she said.

At the same time, more than 1,000 concerned beachgoers have reported dead and sick marine mammals to the Channel Island Marine and Wildlife Institute, a nonprofit conservation organization that rescues and rehabilitates marine animals. Volunteers responded to the calls capturing the distressed animals in nets so that they can be transported to the center of the institute for treatment.

“We’re doing our best to keep up with the intense pace,” said Ruth Dover, general manager of the Wildlife Institute. told the National Oceanic and Atmospheric Administration. “Please continue to report all sick and injured marine mammals as we reach as many animals as possible as quickly as possible every day,” she said.

Conservation groups are still awaiting test results to confirm what is making the animals sick, but their symptoms, combined with high levels of domoic acid from Orange County to San Luis Obispo County, indicate the toxin is the likely culprit. Although algal blooms occur naturally, human activities that disrupt ecosystems are believed to play a role in their more frequent occurrence and increased intensity. This includes pollution and climate change, according to the NOAA.

A similar episode in August led to the stranding of dozens of sea lions. Large numbers of marine mammals also died from the poison in 2015 and 2007.

Domoic acid does not affect humans unless they consume it in contaminated seafood, such as clams or crabs. The California Department of Public Health occasionally closely monitors fishing for toxins they close. Department last week warned against eating clams, clams or scallops harvested recreationally from Santa Barbara County after “dangerous levels” of domoic acid were detected in the shellfish. a quarantine on such clams from along the California coast is also in effect.

Ms. Berman Kowalewski, the dolphin biologist, said she and her team are overwhelmed for now, but would continue to respond to the grim calls and try to study dolphins more deeply, hoping the algal blooms will eventually subside.

“I’m tired. I’m exhausted,” Ms. Berman Kowalewski said. “Another way I see it is that events like this don’t happen that often. So when we have times like these, it’s important for us to try as much as possible gain knowledge.”