Marine Mammal Center stranding rescue volunteer Lincoln Shaw captures a stranded California sea lion at North Rodeo Beach in Sausalito. (Stephen Lam / The Chronicle)

Jane Kay, Chronicle Environment Writer Fluctuating ocean conditions may be depleting the food supply of young sea lions that are turning up skinny and ill on California beaches, mirroring the fate of Brandt’s cormorants earlier this spring. The animal strandings are so numerous that the newly expanded Marine Mammal Center in Sausalito can’t keep up. Only those young sea lions most in need of help are being brought in for treatment – up to 20 a day – leaving others to try to make it on their own, center representatives say. Scientists agree that the youngsters, born nearly a year ago on the Channel Islands off Southern California, aren’t getting enough food. But they’re at a loss to determine whether the sea lions’ favorite foods – northern anchovies and sardines – are hard to find because they’re moving south in response to falling and rising ocean temperatures. That’s the suspected scenario for the Brandt’s cormorants. More than 500 of the birds, which also eat the anchovies and sardines, were picked up starving or dead in April and May by the Farallones Beach Watch program. Or scientists wonder whether a U.S. record number of pups born last year on the Channel Islands means there are more around to fail during the sensitive transition from nursing to hunting for food on their own. Drawing global interest is yet another theory: that the marine mammals and the seabirds are signaling an early warning of an El Niño, the warm-water current from the tropical Pacific. … As of Thursday, the Marine Mammal Center had 136 patients in its new $32 million center, which opened to the public Monday. Of the patient load, 85 were sea lions receiving nourishment through feeding tubes and treatment for organ failure and other problems. By comparison, there were 53 sea lions under care two weeks ago. “They’re just too weak to try to forage. You can see their bones,” said center spokesman Jim Oswald. So many beach reports are coming in that the center has to choose where to respond. There aren’t enough trained rescue crews or vehicles to bring in – or even check on – every animal, he said. …

Sick sea lions present a mystery