"We are likely to see more local events like this if sardines disappear or redistribute along the coast and into deeper water," said Selina Heppell, a fisheries ecologist at Oregon State University.
Biologists also suspect the drop is hurting brown pelicans that breed on California's northern Channel Islands. The seabirds, which scoop up sardines close to the ocean surface, have shown signs of starvation and have largely failed to breed or rear chicks there since 2010.
Brown pelicans were listed as endangered in 1970 after they were pushed nearly to extinction by DDT, which thinned their eggshells. They were taken off the list in 2009 and now number about 150,000 along the West Coast.
Though pelicans have had more success recently in Mexico, where about 90% of the population breeds, environmental groups think the lack of food at the northern end of their range could threaten the species' recovery.
Normally, pelicans and sea lions would adapt by instead gobbling up anchovies. But aside from an unusual boom in Monterey Bay, anchovy numbers are depressed too.
"That does not bode well for everything in the ocean that relies on sardines to get big and fat and healthy," said Steve Marx, policy analyst for the Pew Charitable Trusts, a nonprofit that advocates for ecosystem-based management of fisheries.
Fishermen also attest to the scarcity.
The West Coast sardine catch oscillates with the market and was valued at about $14.5 million in 2013, according to the National Marine Fisheries Service. But California fishermen pulled in just $1.5 million worth of sardines last year, preliminary data from state Department of Fish and Wildlife show.
Just a few years ago, Hanson, the sardine captain, didn't have to travel far from port to pull in nets bulging with sardines.
Not anymore. If his crew catches sardines these days, they are larger, older fish that are mostly shipped overseas and ground up for pet or fish food. Largely absent are the small and valuable young fish that can be sold for bait or canned and eaten.
Still, when he embarked for Catalina Island on a December evening, Hanson tried to stay optimistic. "We're going to get a lot of fish tonight," he told a fellow sardine boat over the radio.
After hours of cruising the island's shallow waters, the voice of another boat captain lamented over the radio, "I haven't seen a scratch." So the Eileen and other boats made an about-face for the Orange County coast, hoping to net sardines in their usual hideouts.
No such luck.
By daybreak, Hanson was piloting the hulking boat back to the docks with nothing in its holds.