Photo: Mathew Sumner / Special To The Chronicle Photo: Mathew Sumner, Special To The Chronicle Photo: Brendan McGuigan Photo: Brian Feulner, Brian Feulner, Special To The Chronicle Photo: Brian Feulner / Brian Feulner, Special To The Chronicle Photo: Brian Feulner / Special To The Chronicle Photo: Brian Feulner / Special To The Chronicle Photo: Brian Feulner / Special To The Chronicle Photo: Brian Feulner / Special To The Chronicle Photo: Brian Feulner / Special To The Chronicle

Already having missed a whole season in 2018, abalone divers won’t be able to resume their sport for at least two more years.

On Wednesday, the California Fish and Game Commission decided to keep the state recreational abalone fishery closed through April 2021 in order to give the shellfish population a chance to bounce back. During a meeting in Oceanside (San Diego County), the commission based its decision on low density surveys — a tool used by biologists to measure the health of the abalone population — from key sites along the North Coast.

“Conditions have only gotten worse since the 2017 surveys,” said Sonke Mastrup, environmental program manager at the invertebrate program of the California Department of Fish and Wildlife, which recommended the extended closure. The season is usually open from April to November for recreational fishing north of the Golden Gate, but has been limited in recent years and was closed completely this year.

As distressing as the situation may be for Californians who love the culture of abalone diving, state biologists say it’s been a lot worse for the slow-growing sea snails themselves, which are starving and not reproducing. The struggling red abalone and dwindling kelp forest on the Northern California coast are prime examples of how warming oceans are hurting the coastal ecosystem, economy and culture.

The trouble really began with the El Niño of 2014-16, the start of what the department has called “extreme environmental conditions”: a massive kelp die-off that was partly due to warming ocean temperatures and also to exploding numbers of purple sea urchins, which compete with the abalone for the bull kelp for food.

Mastrup said that despite the low abalone density, biologists and fishermen who monitor the situation are starting to see renewed kelp growth in a few sites.

The Department of Fish and Wildlife recommended that the fishery remain closed to allow the population to recover while it prepares a new management plan. The closure will cost an estimated $15 million to $25 million to businesses frequented by abalone divers, including hotels, campsites, restaurants and sports equipment rental shops in coastal towns where diving is popular, according to an economic impact statement from the Fish and Game Commission.

In 2017, the season was shortened by two months, to May to October instead of the usual April-to-November season. Between 2002 and 2015, the average take of abalone north of the Golden Gate was estimated at 241,000 annually, according to the Department of Fish and Wildlife.

Earlier this year, the Fish and Game Commission changed the rules to allow recreational divers to take up to 20 gallons of purple sea urchins a day from the waters off of Sonoma and Mendocino to see if that would aid in the recovery of the bull kelp and abalone. In one case, experienced divers used a vacuum device to suck the creatures from the ocean floor.

A group of avid abalone divers, who monitor the different fishery regulations with the closeness of sports fans following a favorite team, have generally expressed support for the continued closure, but some have suggested that a small number be allowed to fish to continue collecting data — and to keep the sport alive.

Photo: Brian Feulner / Special To The Chronicle

“A small fishery will allow fishermen to continue their tradition of abalone fishing,” said diver Jack Likins of Gualala (Mendocino County), who traveled to Oceanside to speak at the meeting. “As you know, there’s no fishery here in Southern California other than the poaching fishery, and I’d hate to see that happen.”

Lifelong abalone diver Steve Rebuck of San Luis Obispo criticizes the department for not taking more action sooner, such as when the abalone density surveys indicated signs that the population was dropping in 2012, partly due to an algal bloom that killed a lot of the invertebrates in 2011.

“It was clear it was a problem,” said Rebuck, a former consultant for commercial abalone diving, when there used to be such a thing. “The department didn’t really address it correctly, in my opinion. They wanted to keep the fishery open.”

Photo: Mason Trinca / Special To The Chronicle 2017

Abalone were once so abundant San Franciscans plucked them from tide pools and cooked them on the beach. Overfishing caused the state to stop commercial fishing in 1997 and to allow only recreational fishing of the shellfish, and only north of the Golden Gate. Red abalone is the only species that can be fished, though there are several more on the coast.

After commercial abalone fishing was banned, abalone farms began springing up around the state, though most of what they produced was sent to Asia until recently. Generally only a few inches wide rather than the minimum 7-inch shell required for collecting wild abalone, the farmed variety is showing up more frequently in Bay Area restaurants.

American Abalone Farms in Davenport (Santa Cruz County), the Bay Area’s main local producer, sells everything it grows and increased its production of abalone a few years back in anticipation of increased local interest (it takes about three years for the shellfish to reach market size), said founder and general manager Tom Ebert.

Ebert said divers often stop by the farm’s store, saying, “I guess this is the only way we can get abalone anymore.”

In Facebook groups, abalone sports divers have been commiserating about the continued closure of the wild fishery. A Sebastopol diver recently posted: “I am just an old abalone diver who is dreaming of getting some more abs before I die.”

Others have wistfully posted historic photos from the 1930s and ’40s. One recent post shows a woman sitting next to gigantic mounds of empty abalone shells in Monterey; another a fully clothed man prying a live abalone off a rock at a California beach.

It’s a level of abundance they know the state will probably never see again.

Tara Duggan is a San Francisco Chronicle staff writer. Email: tduggan@sfchronicle.com Twitter: @taraduggan