Scientists Baffled by High Sea Lion Death Count in a Non-El Niño Year

sea lion

It’s not unusual in California to see from 1,500 to 2,000 sea lion deaths on our beaches each year. But this year is off – way off – and no one can figure out why.

Starting in May and continuing through September, an unexpected onslaught of emaciated, young sea lions has been beached along the coast, requiring a tremendously heightened response among the marine mammal rescue networks throughout the state.

The National Oceanic and Atmospheric Administration (NOAA), which coordinates these networks, is just as concerned about what is happening offshore at sea lion breeding colonies in California’s Channel Islands: Unusually high levels of mortality among the 59,000 pups born in this past spring.

“In one study area, 6,000 pup mortalities were observed where the average had been 1,000 to 1,500,” said Jeff Lake of NOAA’S National Marine Mammal Lab (NMML).

Beach goers have seen – and smelled – the signs that something is amiss. I’ve spotted many carcasses myself throughout the summer months and was surprised to encounter so many visitors soaking up surf and sand and picnicking on rocks amid rotting, decomposing mammals.

The rank smell just about knocked me out while exploring Costanoa with my husband. And in recent days, I’ve passed several rotting sea lions on the beach at Fort Funston, where I run. Naughty dogs go wild, barking and sniffing those sad decaying bodies with empty, hallowed-out eyes.


“We refer to marine mammals as a sentinel species that is like us and can provide a barometer of what is happening to our own ecosystem,” Trevor Spradlin of NOAA’s Washington D.C. office  tells me. “The sea lions have tapped out with a record number of cases of the mammals starving and since it cannot be linked to an El Niño, folks are scratching their heads.”


Perhaps puzzling now, the deaths are typical during an El Niño, such as the one experienced in 1997-1998, due to changes in water surface temperatures and a lack of upwelling.

Ocean upwelling is the mixing of deep cold water at the bottom of the ocean with warm water at the surface so that the cold water and nutrients that fertilize aquatic plants that form the food web can rise to the surface layers while warm water travels to the mid to deep depths. Such areas are very rich along the coast and that is where you find the anchovies, squid and sardines pinnipeds feed on.

While this isn’t the time for such a cycle, scientists are still seeing the oceanographic changes caused by the dying of winds in late April and June. There was no way to pull the vital nutrient-filled waters to the surface. This has been a large contributor to the starvation.

“A huge number of pups were born this year in the Channel Islands and the breakdown in the upwelling may have resulted in the fish moving to other areas inaccessible to young sea lions looking for food for the first time,” observes Joe Cordaro, a wildlife biologist and marine mammal strandings coordinator at NOAA National Marines Fisheries Southwest Regional Office in Long Beach, CA.  “Unlike the older animals, the young pups cannot follow the fish wherever they go.”

Cordaro says scientists also are considering the theory that upwelling has been so great, it has acted like a conveyor belt transporting nutrients to other areas. Either way, he agrees, nature is acting just like it does in an El Niño.

“We do have one developing in the Tropics, and if it continues to develop, it will be nothing compared to what we are now seeing in strandings and deaths,” says Cordaro. “It will pretty much wipe out the reproductive year, slowing down the rate of increase in the population.”

He adds that there is no way it will make a huge dent in the population, itself, because the sea lions have been increasing since the last El Niño with the current population of California  sea lions at about 239,000.The big mystery is why the lack of upwelling has occurred in some areas while not in others.

An investigation into the mystery is being led by Dr. Frances Gulland, Director of Veterinary Science at the Marine Mammal Center in Sausalito. No one knows yet if any of this can be attributed to climate change. They do know that nothing like this occurred last year.

Meantime, beach visitors are asked to continue reporting sea lion strandings to the Sausalito center (415)298-SEAL rather than trying to coax mammals back into the water. Also, always stay back from the dead mammals found on the beach and keep your dogs away, as well.

For animal removal, you should contact the beach maintenance service in your city. Some have policies of removing the carcasses, while others allow them to remain, despite the ghastly smell.

birds flicker

While the dead animals provide food for sea birds and fowl, the sea lions are usually contaminated from pesticides and other toxins dumped into our oceans over time. Cordaro says it isn’t in the best interest of scavengers to feed on the carcasses.

“They don’t die from eating contaminants but their eggs become thin and crack before hatching,” he says. “It effects the reproduction of the next generation.”

Main Image: Luanne Bradley

Image One: Vanilla Sheikh

Image Two: NOAA

Image Three: Quarterdome

Luanne Bradley

Luanne Sanders Bradley is the West coast Editor at EcoSalon and currently resides in San Francisco, California.