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Fewer Sea Lion Pups Are Stranded This Year in California — Because So Many Died Last Year

The declining sea lion population is an ominous sign of warming temperatures in the Pacific Ocean, which have been exacerbated by one of the most severe El Niño formations on record.
Photo by Peter Dasilva/EPA

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Sea lion pup strandings are down significantly from this time last year — but that's actually bad news. The pups aren't striking out on their own to wash up hungry, cold, and disoriented along California shores in great numbers yet this year because most of them are already dead, according to scientists who study the animals.


The deteriorating pup situation is an ominous new sign of the havoc created by a warming Pacific Ocean on the mighty sea lion population and the fish the animals need to survive.

The Channel Islands off the coast of southern California where the animals are born have been littered with thousands of pup corpses.

"There are a lot more dead. We haven't ever seen anything like this," said Sharon Melin, wildlife biologist of the Alaska Fisheries Science Center of the National Oceanic and Atmospheric Association (NOAA) in Seattle, which has tracked the pups on their island rookeries since 1979.

"What's really disturbing are the pups still alive," said Melin. "They're racks of bones working so hard to survive and trying to suckle from mothers that aren't theirs."

Related: Thousands of Sick Sea Lion Pups Are Washing Up Along the California Coast

The pups, which stay with their mothers and nurse for 10 months to wean in April, haven't gained any weight since they were three months old in September — when they already weighed in well below average.

Birth rates were already down to begin with because in many cases hungry adult females were unable to sustain their pregnancies.

Melin estimates the survival rate for the pups will be 20 percent, though NOAA won't have mortality and birth rate statistics until later in the year.

Some mothers are managing to continue to feed their pups but only enough to just maintain their weight. "They're not thriving," said Melin. She predicts there could be significant strandings later in spring, but "the pups will be so underweight they'll have almost no chance of survival. They won't have the weight or the energy to hunt."


The biggest negative impact on the sea lion population will come when 2015's pups begin to reproduce, warned Melin.

As cute as stranded pups might be, a high number of incidents is a significant sign of a species in dire straits. Last year was a record for strandings, with a total of 3,340 pups washed up on shores in distress — more than the previous five years combined.

So far this year 375 pups have stranded, still above the average 160 for the first two months of the year, according to the latest statistics from NOAA, but down significantly from last year. The Marine Mammal Center in Sausalito was treating 100 sea lion pups at this time last year, and now has two. The pups are apparently to weak to even strand or are gone already.

Related: We've Passed Peak El Niño — But Many More Months of Extreme Weather Is Likely

Nursing pups are driven to strike out too early on their own because they're starving, after being left too long by mothers desperately trying to feed themselves as they hunt for vanishing fish populations.

Fisheries are declining and being driven away from the coast by a persistent "warm blob" of coastal water from Mexico to Alaska that appeared last year and "totally took us by surprise," said Meilin. El Niño is exacerbating the ocean warming.

Unlike male sea lions, which are able to follow fish wherever they may be, mothers are tied to their pups and must hunt close enough to return frequently to nurse — so they're dependent on the abundance of local fish. But because of the abnormally warm ocean temperatures, females must dive deeper or swim farther from shore to seek the fish in colder water.


"There are consequences for either," Melin said. "The deeper dives demand more energy stores, the longer distance means the mothers will be away for days from their pups."

Sea lions typically eat sardines, anchovies, hake, rockfish, and squid. But they're opportunistic feeders and will eat what's available, even to the point of making some "desperate diet decisions," like eating tiny pipefish that are far less nutritious, said Melin. There's still a chance surviving pups can be saved if there's a change in fish availability closer to the rookeries, but it's difficult to predict. Jack and Pacific mackerel appear to now be moving close to the sea lion feeding grounds near San Miguel and San Nicolas Islands where the pups are born and could represent a good food source for the moms.

Melin believes the sea lions will adapt to even a permanently altered coastal Pacific that has been "consistently and persistently" warm, but at smaller numbers than the animals' current 300,000 — and dropping — population.

"It's going to decline," she said. "We don't know how much or how quickly, but it's going to happen. And it's going to take a number of painful years."

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