Larry Derr was as prepared as any longtime Southern California bait fisherman for the disappearance of the Pacific sardines he has pulled up by the ton since the 1980s.

He can fish anchovies instead and, if those become scarce, there’s been a local surge in market squid to keep him in business.

But the fickle sardines have been so abundant for so many years — sometimes holding court as the most plentiful fish in coastal waters — that it was a shock when he couldn’t find one of the shiny silver-blue coastal fish all summer, even though this isn’t the first time they’ve vanished.

And the similar, but smaller, anchovies have proven a poor replacement since sardines became scarce. Fortunately, a boom in market squid has propelled Derr and other coastal pelagic fishers.

In three days of nighttime fishing last week, Derr barely cleared a measly 20 scoops of anchovies to sell.

“A couple days ago we caught a ton of anchovies,” Derr said, keeping a vigilant eye for the telltale red mass on the In-Seine’s sonar during a predawn hunt Saturday. The screen remained black with irregularly dispersed green dots representing schools too small to fish. “We want this to be solid red.”

Though sardines aren’t as valuable as tuna or rockfish, they’re an important food source for larger fish, marine mammals like sea lions, dolphins and whales, and sea birds that can spot them from the air and dive for them. Some have attributed recent rashes of sea lion pup and pelican deaths to the sardine population decline, which began a few years ago and was officially recognized in December when the fishing quota was dropped to just 5,446 metric tons for all of California, Oregon and Washington from January to June. In the same time period last year, the quota was 18,073 metric tons.

The Pacific Fishery Management Council lowered the quota in November after years of sardine stock decline from 2006, when 1.4 million tons were estimated to be swimming around the north Pacific. This year, their numbers are believed to be less than 400,000 metric tons.

This isn’t the first sardine fishery collapse. A booming sardine fishery based in Monterey’s Cannery Row ended suddenly when the fish simply stopped appearing in their usual haunts. The loss of the fishery, partially chronicled in John Steinbeck’s 1945 novel “Cannery Row,” was a shock to the local economy.

Decades of research into what happened to the sardines and whether overfishing was to blame followed. Then, sardines started appearing as by-catch in the 1980s. By the 1990s, they were back in full force and — except for some low points — have remained so plentiful that “you could almost close your eyes, throw out a net and find sardines everywhere,” Derr said.

Kerry Griffin, staff officer on coastal pelagic fish species for the National Oceanic and Atmospheric Administration, said all sardine fishing will be banned if the population estimate decreases by about half of what it is now.

For now, environmental scientists are looking to April, when they will have an updated assessment of the amount of living sardines.

“Is it El Nino? Pacific Decadal Oscillation? El Nina? Long-term climate change? More marine mammals eating sardines? Did they all go to Mexico or farther offshore?” Griffin said. “We don’t know. We’re pretty sure the overall population has declined. We manage them pretty conservatively because we don’t want to end up with another Cannery Row so, as the population declines, we curb fishing.”

There is heated debate surrounding the sardine decline. Some environmentalists believe they have been overfished in recent years, though the scientists who monitor them generally say the fish simply haven’t tolerate cooler waters well — a theory based on the temperature of coastal waters dubbed Pacific Decadal Oscillation.

Russ Vetter, director of the Fisheries Resource Division at NOAA’s Southwest Fisheries Science Center, said the most probable scenario is that cooler waters made it harder for the babies to survive.

“They haven’t had a good recruitment,” Vetter said, referring to the survival of young sardines. “You have to have adults that produce the eggs and then environmental conditions that would allow them to grow and then to not have them eaten by pelicans and terns, etc. It’s always complicated about why a fish egg doesn’t make it through the problems but we do know that, when the ocean is on the cooler side, conditions aren’t right.”

In the meantime, most fishers are concentrating their efforts on market squid, which are now plentiful. Anchovies and mackerel are also filling the void locally.

“Everybody’s calling me every day for sardines,” Derr said. “They’re all gone. Even Monterey Bay Aquarium is still waiting for some to restock one of their exhibits.”

While scientists debate when and if the sardines will return, Vetter said no one can know for sure. The fish reproduce so rapidly that their numbers can boom incredibly fast, he said.

In the meantime, the appearance of large numbers of squid has kept fishers in San Pedro, Redondo Beach and Marina del Rey happy.

“But, if the squid go away, it’s a real problem if they can’t fall back on something else to fish for,” Griffin said.