Environment & Science

Sea lion pup strandings may hit 2,000, but don't blame climate change (yet)

Sea lion pups photographed at Point Dume on March 9, 2015. One (bottom) is believed to be dead.
Sea lion pups photographed at Point Dume on March 9, 2015. One (bottom) is believed to be dead.
Jordan Miller
Sea lion pups photographed at Point Dume on March 9, 2015. One (bottom) is believed to be dead.
Sea lions photographed at Point Dume on March 9, 2015
Jordan Miller
Sea lion pups photographed at Point Dume on March 9, 2015. One (bottom) is believed to be dead.
Many sea lion pups in California's Channel Islands are underweight and are washing up on beaches starving are dead. Biologists suspect unusually warm ocean conditions are reducing marine productivity, causing female sea lions to struggle to find sufficient food to nurse the pups.
NOAA Fisheries/Alaska Fisheries Science Center

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California sea lion pups keep washing up on the state's coastline at abnormally high numbers: more than 1,800 starving pups have been brought into rescue facilities already this year, officials reported Tuesday.

The average yearly intake for stranded pups is about 200.

Justin Viezbicke, California Stranding Network coordinator for the National Marine Fisheries Service, said that he's asking the public to be patient when it comes to rescue attempts for emaciated pups.

He said that the network won't be able to rescue all pups and efforts to do so would hurt its ability to treat animals already in house. About 750 sea lions are being held for treatment in facilities right now.

“If we go over too many animals, the care really is lessened for all of those animals, and they all have decreased chances of survival,” Viezbicke said "Whereas, if we can focus on the ones we know we can give the best care and have the best chance of survival, we at least are giving them the best shot."

Even reaching treatment centers is no guarantee of survival for the pups. Some are judged to be too far gone and are euthanized. Others die while undergoing treatment.

Even the ones that are successfully treated and released face difficult survival prospects. Unusually warm water off the coast holds less prey for the sea lions to forage.

“The reality is we’re putting them back into a very challenging situation, so there’s no guarantee that these animals that are being rehabbed are going to survive. It’s something we’ll be watching and monitoring for the future,” Viezbicke said.

The warm water is believed to be the cause of the high number of strandings in the first place.

As nursing mothers spend more time away on hunting trips seeking out that ever elusive prey, starving young leave their rookeries far earlier than they normally would.

Scientists said that the population of California sea lions is still strong, with estimates of total size at around 300,000 individuals.

The population has doubled from decades ago and the increased competition may be contributing to the poor feeding conditions, according to Nate Mantua, a climatologist with NOAA Fisheries.

Climate change not culpable … yet

He said the warm water isn't likely caused by global warming because its development was too recent and too regional.

“It doesn’t look to me like a global warming pattern. It’s a direct response to the regional wind patterns that have been so persistent — including the pattern that brought us drought,” Mantua said. “I don’t really see the hallmarks of a global warming signature.”

A lack of winds from the north has kept surface water from being pushed out from the coast. That has lessened the amount of nutrient-rich upwelling of colder water.

Map of warm water
The sea surface temperature map shows the unusually warm ocean water encompassing the West Coast. Darker red indicates temperatures farther above average. Credit: NOAA Fisheries/Southwest Fisheries Science Center.

No end in sight

Mantua said the northerly winds that normally accompany the start of spring are beginning to appear in Northern California. If they persist, he said some colder water could emerge nearer to land. That could help.

But he said the effect would be localized and that a recently declared El Niño appears to be strengthening — a combination that means the warm water could last for another year.

“The bigger picture, you step back and look at the whole broad region of the Northeast Pacific Ocean, it’s likely to stay warm for much of this year," he said.

"Unless we get a winter next year that’s more normal and a lot stormier," he added, "I think that it might persist. And if the El Niño develops, then it becomes even more likely to persist all the way to the end of the year and to next spring."

Even though climate change isn’t a large factor in the current water temperature rise, Mantua said models predict it will become the major cause for future warmer water.

“When we get towards the middle of this century, human-caused climate change is going to be equal and then dominant for the warming trends along the West Coast,” Mantua said.

2013 was bad, too

This is the second time in a few years that California sea lion pups have stranded at abnormally high rates. In 2013, NOAA declared an unusual mortality event for the species.

Viezbicke, of the California Stranding Network, said it would take several years of similar mass deaths to reduce numbers to a threatened level because sea lion populations are so big right now.

In fact, events like this may even strengthen the remaining population.

“Even in naturally occurring situations like this, Mother Nature can kind of control the population size out there, and those that are doing well — that are currently in this warm water situation — will probably continue to do ok,” Viezbicke said. "And those that don’t, will kind of be weeded out from the gene pool."