Hundreds of Sea Lion Pups Are Dying off California’s Coast, and Scientists Don’t Know Why

Hundreds of Sea Lion Pups Are Dying off California’s Coast, and Scientists Don’t Know Why

UC Santa Cruz researchers are studying why seal pups are dying near Año Nuevo Island, midway between San Francisco and Santa Cruz. (Patrick Robinson/UC Santa Cruz)

Jill McLaughlin

Jill McLaughlin

5/25/2024

Updated: 5/28/2024

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Hundreds of dead sea lion pups have washed ashore this spring near an island off the California coast, and researchers are trying to find out why.
“We’re seeing something abnormal,” University of California–Santa Cruz researcher George Colaco told The Epoch Times.
Aerial surveys of the sea lion herd near Año Nuevo Island, midway between Santa Cruz and San Francisco, show at least 300 dead pups in the past three weeks, according to Mr. Colaco.
The mammals haven’t even reached peak pupping season, which is usually about mid-June.
“We don’t understand what’s going on right now,” he said.
The area usually gets about 700 to 800 new pups starting in June, with only about five to 10 mortalities, according to the researcher.
Last year, a fast-growing toxic algae bloom off Southern California was likely to blame for the deaths of hundreds of California sea lions and nearly 60 dolphins, according to the National Oceanic and Atmospheric Administration’s June 2023 report.
Researchers with the university’s Costa Lab in Santa Cruz studied whether toxic algae blooms were also responsible for the pup deaths, but results didn’t confirm the theory, according to Mr. Colaco.
The scientists reached out to government agencies and other researchers doing similar work in California and discovered that similar stillborn deaths were happening in other places, including among breeding colonies on San Miguel Island in Santa Barbara County. The cause of the mortalities remains a mystery.
“We haven’t seen any results that point to one reason,” Mr. Colaco said. “It could be a combination of things.”
A sea lion herd off Northern California. (Patrick Robinson/UC Santa Cruz)

A sea lion herd off Northern California. (Patrick Robinson/UC Santa Cruz)

Adult sea lions could have leptospirosis, a disease caused by bacteria in contaminated water or soil, or avian influenza virus, also called H5N1 or bird flu.
The highly infectious bird flu has adapted and spread between birds and marine mammals in South America, posing an immediate threat to wildlife, according to the University of California–Davis, which published a study about the issue in February.
The disease killed about 5,200 sea lions on the beaches of Peru in 2023, the Centers for Disease Control and Prevention reported in October.
Santa Cruz researchers have tested several samples from the dead sea lion pups and haven’t found any specific disease related to the deaths, Mr. Colaco said.
Another theory points to the weather phenomenon called El Niño, which happens when the Pacific Ocean surface warms.
The herd of pregnant female sea lions has increased, reaching the maximum of what the environment in the area can support. The strain on food supplies might be causing some of them to abort their pups early.
“It will be interesting to see our surveys next month, to see how many pups do survive,” Mr. Colaco said.
He reminded beachgoers to report anything out of the ordinary on the shores, including dead pups.
People are encouraged to call 866-767-6114 to report dead, injured, or stranded marine mammals.
Researchers have tested samples from the dead sea lion pups and haven’t found any specific disease related to the deaths. (Patrick Robinson/UC Santa Cruz)

Researchers have tested samples from the dead sea lion pups and haven’t found any specific disease related to the deaths. (Patrick Robinson/UC Santa Cruz)

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Jill McLaughlin

Jill McLaughlin

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Jill McLaughlin is an award-winning journalist covering politics, environment, and statewide issues. She has been a reporter and editor for newspapers in Oregon, Nevada, and New Mexico. Jill was born in Yosemite National Park and enjoys the majestic outdoors, traveling, golfing, and hiking.

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