Oceana: Blame sardine overfishing, not just warmer waters, for sea lion deaths.

The Sausalito-based Marine Mammal Center counted 170 sea lion pups in its care earlier this month. (In a normal year, they have about 12.)

They're among some 1,200 sea lions sent to rehab facilities in California this year, MMC reports:

"We have never seen so many sea lions stranding this early in the year at such a young age and in such poor condition. This is especially concerning because California sea lions are considered sentinels of the sea; their struggles are often an indication that something more complex is happening in the ocean environment."

This is the third consecutive year that starving sea lion pups have stranded along the state's coastline in high numbers. But scientists aren't totally sure why.

One likely factor: Warm water patches along the U.S. West Coast. Unusual wind conditions are suppressing the natural cold-water upwelling that, in a normal year, brings lots of fish (read: sea lion food) to the surface.

Compounding the warming: El Niño conditions, which the National Oceanic and Atmospheric Administration made official March 5. Climatologists are measuring some of the warmest ocean temperatures on record in parts of the tropical Pacific, at 2-5 degrees Fahrenheit above normal for the season. That means warm coastal waters could stick around through the summer or longer, redistributing the forage fish sea lions depend on.

As a result, MMC reports, sea lion mothers are taking longer to forage for prey while their nursing pups wait for them, hungry. Some pups lose patience with the wait and set off on their own, washing up weak, thin and alone on California beaches.

But marine conservation nonprofit Oceana, which has a California office in Monterey's Heritage Harbor, connects another dot to the scarcity of sea lion food: sardine fishing. The Pacific Coast sardine population is at its lowest level in 15 years, Oceana reports.

“Any fishing on Pacific sardine right now is overfishing,” said Geoff Shester, Oceana California campaign director.

Oceana's argument: When natural ocean conditions drive down the sardine population, fishing pushes it even lower, making it harder and slower for the population to rebound when ocean conditions become favorable to sardines again.

"While federal officials are quick to blame ocean conditions for the declines in [sea lion] prey, they have turned a blind eye to the effects of sardine fishing and even voted to increase harvest rates on sardines," states an Oceana press release.

To some extent, Oceana's pressure worked: On March 10 the Pacific Fishery Management Council, a federal agency that manages fisheries on the West Coast, banned new commercial fisheries for seven forage species in federal waters from Washington to California. 

The protected fish species include herring and squid, but not sardines or anchovies, the food some very hungry sea lion pups would probably like to snack on right about now.