Dead sea lions appear along California’s coastal islands. Researchers aren’t sure why

On May 7, Patrick Robinson took a boat to Ao Nuevo Island to observe the sea lions that give birth on this rocky outcrop north of Monterey Bay.

The shore was littered with stillborn babies who looked like they had been born too early and were therefore too weak and small to nurse, or had died at birth.

Similar sightings were being made further down the coast of San Miguel Island in the Channel Islands, where massive colonies of sea lions congregate each year, and as far south as Mexico.

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Robinson, the director of UC Santa Cruz’s Ao Nuevo Reserve, said it’s not unusual to see a few dead cubs this time of year. He said sick or malnourished women occasionally stop on their way south to have abortions. But the numbers he was seeing were alarming. And with peak birthing season still weeks away, it heralds a potentially serious and worrying situation.

Coordinators and biologists stranded up and down the California coast say it’s clear something is going on, but they still don’t know what.

Tests for the bird flu that has decimated populations of sea lions and elephant seals in South America are being processed. So are tests for domoic acid, which has poisoned large numbers of sea lions in the past, as well as other common pathogens.

In a typical year, one can expect to see 5 to 10 dead puppies, said Megan Moriarty, a veterinarian at UC Santa Cruz. But now we have counted 250 to 300 dead sea lion cubs on Ao Nuevo Island.

She said the sightings included dead or stillborn puppies, aborted fetuses, malnourished puppies and adult females with difficult birth dystocia, who are also weak.

Unfortunately, premature dead pups have also been reported in the Channel Islands (San Miguel), which is an important nursery area for California sea lions, she said. The cause and impact of these deaths remains unknown.

She and Sharon Melin, a research biologist at the National Oceanic and Atmospheric Administration’s Alaska Fisheries Science Center, said there are many possible reasons for the widespread mortality of sea lion pups, including environmental factors such as malnutrition, lack of available food due to El Nio. infectious causes (bacteria, viruses such as leptospirosis, influenza, brucella, cocciella and others) and toxins (such as domoic acid).

And although both think testing for avian flu is warranted given that it’s a global, multi-species outbreak, we haven’t seen any neurological or respiratory signs in the sea lions at Ao Nuevo, Moriarty said.

Reproductive failures and stillbirths have not been a common finding with influenza A infections in marine mammals globally, she said.

Melin said about 25,000 puppies are born in the Channel Islands each year.

In some years, especially El Nio years, or sometimes heat wave years or other freaks that happen well in the environment, they have about 20% to 30% premature pups, she said.

She said cubs born at this time of year are often not fully matured.

They just might last a little longer … and maybe if you can put them in an incubator and take care of them, they might survive, she said.

And when they do necropsies on these little puppies, you’ll see that the last thing to fully develop are their lungs. … So they’re just not fully developed enough to breathe on their own and be successful. They will sometimes live for a few days at this point, but cannot nurse and lack the motor skills to hold their head up or nurse effectively.

She said mothers will usually try so hard to get their babies to breastfeed, they don’t know what’s going on and they’re trying to figure out why they’re not breastfeeding. So there’s a lot of interaction going on there, but usually the pup ends up dying after a short period of time.

Michael Milstein, a spokesman for the National Oceanic and Atmospheric Administration, said the most recent fisheries survey found significant anchovy declines in the southern half of the state, where most of the impoundments are located.

He said sightings of raptors and seabirds were more scattered, suggesting they are tracking more widely dispersed prey. He said that polls in the north have not been completed yet.

But the high number of brown pelican deaths and the steep decline in California’s chinook salmon populations have many worried about broader ecosystem problems.

This year, fisheries managers decided to stop salmon fishing along the coast and in rivers for the second year in a row, looking to help chinook stocks recover.

Coordinators and biologists say the good news is that California’s sea lion population is healthy and strong; however, rescue centers are overflowing with sick and malnourished puppies.