The days are getting shorter, pumpkin spice lattes are here and once again, it’s time for that other Bay Area rite of fall: worrying about the levels of toxins in local Dungeness crabs.

With the state’s recreational Dungeness crab season scheduled to start Nov. 3 and the commercial season Nov. 15, the California Department of Public Health has released preliminary test results on Dungeness crab for domoic acid, the neurotoxin that caused delays in two of the past three crab seasons in the Bay Area.

So far, elevated levels of domoic acid were found in five Dungeness crabs collected from Bodega Bay and Trinidad (Humboldt County) in late September and early October, which is the most recent data available. The San Francisco, Half Moon Bay, Monterey and Morro Bay regions were clean in this round of tests. Testing will continue in the coming days and weeks.

“The California Department of Public Health is monitoring domoic acid levels to ensure a safe food product for consumers,” said Corey Egel of the department’s Office of Public Affairs. “At this time, it is too early to determine if reported levels may have any impact on the recreational or commercial Dungeness crab season.”

In Oregon, recreational crabbing was shut down Oct. 15 due to domoic acid after state officials found high levels during testing. It remains closed from the California border north to Cape Blanco.

Domoic acid is a byproduct of algal blooms that form when ocean temperatures are warmer, and it can cause illness and even death in marine animals and humans. Though common in the summer and early fall, the blooms usually dissipate by the time Dungeness crab season begins in November. In recent years, however, climate change and El Niño conditions have caused warmer sea surface temperatures to linger into winter, and along with them, domoic acid. The California Department of Public Health defines elevated levels of domoic acid as more than the federal action level of 30 parts per million.

“Yes, the data have been showing warm anomalies along the Northern Coast, and we have seen domoic acid spike upwards in Humboldt Bay — but not Monterey Bay — so there are definitely some localized hotspots developing,” said Raphael Kudela, an algal bloom specialist and Lynn Professor of Ocean Health at UC Santa Cruz, via email. “But we aren’t expecting large warm anomalies this year. They may develop next year, however.”

Nonetheless, oceanographers are monitoring conditions that could cause warmer ocean temperatures to stay around again this winter, such as the development of a blob-like feature off the coast of Alaska. The concentration of warm water caused by high pressure bears similarities to the one off the California coast from 2013 to 2015 that many believed to be a factor behind California’s drought.

In addition, the National Oceanic and Atmospheric Administration just announced a 70 to 75 percent chance of an El Niño forming this winter. The warmer water temperatures during the El Niño system that began in 2014 led to delays in the 2015-2016 Dungeness crab season as well as the collapse of the sardine population.

Other parts of the California coast have showed signs of unusually warm conditions in recent months. In August, the warmest ever ocean temperatures were reported in San Diego. Last week, biologists reported a growing outbreak of a bacterial infection in California sea lions that is attributed in part to rising sea surface temperatures.

The state Department of Public Health tests domoic acid levels in Dungeness crab from California ports every one to two weeks. Tests have to be clean for two weeks before the crab from that area are determined safe to eat. In the 2017 calendar year, $47 million in Dungeness crab was landed in California.

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