Why are hundreds of clams showing up on SLO County beaches? Here’s what scientists say
A kindergartner scurried across the sand at Pismo Beach on Friday, scooping palm-sized clams into a bucket to carry back to the ocean.
Meanwhile, a seagull swooped out of the fog to pluck a clam from the shore, trotting a few paces before tearing it open for lunch.
“It’s bizarre,” said Santa Maria resident Debbie Jackson, who spotted hundreds of clams on the sand in Pismo Beach. “It seems like every step you go, you’ll find them.”
Usually, Pismo clams burrow a few inches beneath the wet sand, using their siphons like snorkels to eat and breathe, according to California Department of Fish and Wildlife environmental scientist Claudia Makeyev.
In recent months, however, Pismo clams have been showing up on top of the sand at San Luis Obispo County beaches.
California State Parks, the state Department of Fish and Wildlife and Cal Poly’s Center for Coastal Marine Sciences are working together to study the shellfish.
“It’s exciting that (the clams are) coming back,” said Ben Ruttenberg, director of the Center for Coastal Marine Sciences. “We’re going to try to get some handle on what’s going on because there is such a strong, emotional attachment to these critters in the area.”
Why are clams surfacing on SLO County beaches?
Pismo clams are embedded in Pismo Beach’s history and culture.
Pismo Beach was known as the Clam Capital of the World in 1947, according to the city’s website.
During the late 1800s, clammers could harvest as many clams as they could haul away, The Tribune reported previously.
Before commercial shipping of clams was banned in 1927, more than 370,000 pounds of clams were annually harvested from beaches stretching from Oceano to Monterey.
In 1911, the first clamming restrictions were passed — limiting the daily take to 200 clams per person. In 1927, folks were limited to 15 clams per person daily, and the clams had to be larger than 5 inches.
Now, a person can only harvest 10 clams per day that are 4.5 inches or larger.
The last legal-sized clams in Pismo Beach were harvested 30 years ago, in 1993, according to the city’s website.
Pismo clams started surfacing on SLO County beaches about three years ago, according to Ruttenberg.
The scientists don’t know exactly why that’s happening, but they are studying a few hypotheses, Ruttenberg said.
The primary hypothesis is that certain algae blooms produce a chemical that clogs the clams’ gills, prompting them to surface.
“All this is very much conjecture,” Ruttenberg said. “We just we haven’t had the scope to go try to run any kind of real experiments in the lab.”
Ruttenberg’s team consistently monitors algal blooms near the Cal Poly Pier in Avila Beach, but they don’t have the funding to monitor algae on the rest of the coast, he said.
“Sometimes, a bloom will sort of extend from Pismo all the way up into Avila, but sometimes you may actually get different species blooming in different places,” Ruttenberg said. “When the clams are surfacing (in Pismo Beach), we just don’t have the logistics and resources to go sample those waters.”
Clam surfacing events are more often reported in the summer, Ruttenberg said, but this may be because low tide occurs in the morning during summer months.
“When there are clams surfacing at 5, 6, 7 in the morning, people tend to be out there pretty regularly (at those hours),” he said.
If clams are surfacing during the morning in the wintertime, he said, “We’ll never know ... because the beach is covered in water” due to high tide.
According to Ruttenberg, Cal Poly students have been monitoring the clam population on a monthly or quarterly basis since 2014 by digging trenches in the sand and counting the bivalves in Pismo Beach.
According to Ruttenberg, the size of the SLO County clam population has grown steadily since the monitoring program started — but there isn’t enough research to explain why.
Warm water caused by El Nino weather patterns from 2014 to 2016 may have supported the survival of newborn clams, he said, or a current may have carried clams from other parts of the California coast to Pismo Beach.
Perhaps appropriate foods were just available at the right time, Ruttenberg said.
“These are all really interesting questions that we want to study,” he said.
Clams are getting larger, but are still too small to harvest
According to Fish and Wildlife Lt. Matt Gill, Pismo clams are also getting larger.
This year, he saw clams 1 inch to 3.5 inches in size, he said.
“It’s a success story,” Gill said. “It has a lot to do with the locals taking ownership” and reporting clam poaching when they see it.
Still, the clams this year are too small to harvest.
Pismo clams must be at least 4.5 inches to legally harvest, Gill said, and clammers must have a valid sport fishing license and measuring device to do so.
A clam takes 8 to 14 years to grow to 4.5 inches during its 20- to 30-year life, Ruttenberg said.
If clammers dig up a clam that’s too small, they must rebury the shellfish immediately, Gill said.
“We want the population to rebuild, and we don’t want anyone getting a ticket,” Makeyev said.
If you see someone poaching clams, call the tip line at 888-334-2258.
What to do when you see live clams at the beach
When live clams surface on the beach, the California Department of Fish and Wildlife encourages folks to rebury them.
Live clams have their shells intact, and can sometimes be seen squirting water or burrowing themselves into the sand, according to Makeyev.
To rebury a clam, dig a small, 2-inch deep hole in the wet sand where the water will reach it.
Then pick up the clam, and look at the hinge side to find its ligament, which is a small, fleshy bump.
Place the clam in the hole with the hinge side facing towards the ocean and the ligament facing up. Then, bury the clam, she said.
This story was originally published September 12, 2023 at 8:00 AM.
