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Why Were Sea Lions Starving?
A record number of pups were found emaciated on southern California beaches this year. Can scientists figure out why—and predict if it will happen again?

The scrawny, furred patients began arriving at Los Angeles’ Marine Mammal Care Center in January, their large, curious eyes peering lethargically at veterinarian Lauren Palmer from emaciated bodies.

At first, Palmer wasn’t worried—she had seen hungry pups before. Sea lions calve in May and June on the sandy, rocky shores of the Channel Islands, off the Southern California coast, and mother sea lions wean their offspring after eight or nine months. Some of the newly independent pups have trouble feeding themselves, and as a result, marine mammal rescue groups expect to see hungry youngsters appearing on mainland shores in the spring, though some beach earlier.

But this year was different. By the end of January, Palmer and her crew were scrambling to rejuvenate more than four times as many animals as they had seen in the first month of 2012, and the pups were in exceptionally bad shape. When the animals arrived, they needed an electrolyte solution to treat their dehydration; then, if they couldn’t eat on their own, volunteers hand-fed them a blended “fish smoothie” two to three times a day.

“When they’re small and they need to be fed, it is labor intensive,” Palmer says. The volunteers donated every extra hour they had; eventually, the center had to recruit and train more help. Meanwhile, the sea lion pups kept coming: 48 by the end of January, 115 in February, more than twice that in March. Palmer was working seven days a week, often into the early morning, going through charts and records to plan how to logistically survive the next day.

And it wasn’t just in L.A. From San Diego to Santa Barbara, beachgoers were phoning local rescue organizations about pups that appeared to be stranded. Jeff Hall, the marine mammal coordinator for the California Wildlife Center, says that usually when people call with concerns about sea lions, they’re unfounded; rescuers often arrive to find healthy animals sunbathing. “People will call us thinking just because it’s out of the water, it’s in trouble,” he says. “But this year it was very easy to tell just by looking at them that something was wrong. Their little shoulder blades and ribs were sticking out.”

Hall and others scooped the tiny creatures up in nets and drove them to rehab centers—first in L.A., then, when those centers hit capacity, to neighboring counties. When those also filled up, Hall and colleagues would just try to help the pups reach a stretch of shore where people wouldn’t stress them out; rescuers put up signs asking beachgoers not to disturb the sick pups. “A number of animals died during that time,” he says, “because there just wasn’t space for them.”

At the end of March, the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service declared the situation an unusual mortality event for marine mammals, which started a federally funded investigation. By mid-May, when the strandings began to subside, rehab facilities in Southern California had admitted more than 1,400 pups, a number nearly five times higher than the historical average for that time of year. As many as a third of the starving sea lions didn’t survive, and many more may have died offshore, uncounted.

It’s not easy for scientists to figure out what’s killing animals that spend most of their lives offshore and out of sight. Of the 60 unusual mortality events declared by NMFS since 1991, researchers have found the cause of fewer than half. Marine biotoxins, poisons produced by microscopic algae, accounted for roughly 50 percent of those, and infectious diseases a quarter. The last three events for sea lions were the result of poisoning by domoic acid, a biotoxin that can build up in shellfish, sardines, and anchovies, and affect the neurological functioning of the mammals that eat them, including sea lions and people. Symptoms include seizures and disorientation, including sea lions wandering inland and walking the streets.

But this year, researchers didn’t see symptoms typical of poisoning or infectious disease, says Sarah Wilkin, an NMFS marine biologist and its stranding coordinator for the Southwestern United States. The sea lion pups weren’t having seizures. And on the whole, they weren’t showing signs of disease, such as breathing problems, runny noses, and diarrhea. NMFS researchers took blood and tissue samples from living and dead pups to test for bacteria, viruses, biotoxins, and other contaminants; they checked their stomach contents—measures that Palmer and her team, in crisis mode, didn’t have the resources to handle.

Now, roughly four months later, NMFS researchers are still compiling the test results. But so far, it seems, the pups weren’t sick; they were just hungry. Many arrived weighing less than half of their normal body weight and were dehydrated. For some reason, they had stopped nursing early and weren’t getting as much food as they needed; in many cases, simply providing the pups with fish seemed to restore them to health.

The question that continues to nag scientists is why so many pups were starving. NMFS biologists are currently studying data they collected the previous year on sea lion food sources—primarily market squid, anchovies, sardines, Pacific and jack mackerel, shortbelly rockfish, and hake—to see if any of those stocks noticeably decreased, or if the timing of their movements shifted. “You almost always have to go back to the research, hoping by accident you collected the right data,” says Russ Vetter, a marine biologist at the Southwest Fisheries Science Center, a research branch of the NMFS. His group performs annual fish surveys—determining how many of each species fishermen should be allowed to take—by using sound waves to measure fish concentrations and counting the percentages of species that researchers pull up in nets. But the annual surveys only reveal large-scale annual trends, as opposed to seasonal shifts in the sea lions’ local prey sources.

Sea lions aren’t picky eaters, says Mark Lowry, a Southwest Fisheries Science Center marine biologist. And that makes it unlikely that changes in any one food source would affect their livelihood. Decades ago, he says, they ate mostly anchovies; now, it’s mostly market squid. “When there’s not as much of one, they switch to something else.”

Clues might lie in the health of the mothers. Another NMFS crew is out on the Channel Island rookeries this summer, assessing the condition of the adult females and their newborns. Results are expected in the coming months. No matter what the scientists’ conclusions, though, one thing is certain: California sea lions are an indicator species that can alert us to previously unnoticed changes in the ecosystem. They aren’t listed as threatened or endangered—they number roughly 310,000 in the U.S.—but “by watching these animals, we can get a broader idea of what’s going on in the ocean environment,” says David Bard, director of the Los Angeles care center, “things that will potentially impact humans.”

At the center, Palmer is still caring for 70 sea lion pups, nine of which can’t eat on their own. “They like to lie in the sun, and they like to snuggle up to each other, and they play and do things that you can relate to—they’re endearing to watch. Very smart,” she says. “I never get tired of working with them.” Still, she hopes the researchers trying to figure out what went wrong this year can provide an answer soon—and tell her whether she needs to prepare for more sleepless nights in 2014.

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image of Kim Tingley
Kim Tingley is a regular contributor to OnEarth and the New York Times Magazine. She has an MFA in nonfiction writing from Columbia University and in 2012 received a Rona Jaffe Foundation Writer’s Award, given annually to six female writers who demonstrate excellence and promise in the early stages of their careers. MORE STORIES ➔
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Just have them hold a geiger counter up to the poor sea lions....
If they were hungry, then it would seem that there was a prey deficit. I was in So.Cal this spring and went fishing on a charter boat to the Channel Islands. The boat had no live bait, we had to use frozen squid. I grew up in So Cal and fished alot over the years and don't recall NOT having live bait ever. Perhaps there was not enough food for a critical period in their lives and they went into a starvation that they couldn't get out of. Not sure why just because some acoustic surveys didn't detect anything abnormal that they would rule lack of food out. The surveys might not be a good index of short term prey scarcity.