Legal-sized Pismo clams are back on SLO County beaches. Are they here to stay?
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- Researchers observed legal-sized Pismo clams returning after decades of absence.
- Clam population spikes trace back to strong recruitment pulses in 2014 and 2021.
- Scientists warn overharvesting could outpace reproduction and reverse recovery.
As the sunrise stained the sky pink on a recent May morning, scientists, fishers and seagulls all searched Pismo Beach for an iconic local species: the Pismo clam.
After practically disappearing from San Luis Obispo County shores in the late 1990s, Pismo clams have returned to the area in healthy numbers, and some even measure 4.5 inches long — the minimum size to harvest legally.
The reason for their resurrection is a mystery the Cal Poly’s Center for Coastal Marine Sciences would like to solve.
Center director Ben Ruttenberg said he’s glad to see a healthy clam population return to the beach.
However, he’s worried that the clams aren’t reproducing fast enough to meet the growing demand of recreational fishing.
“When you talk about the tragedy of the commons, it is a classic, classic problem for fisheries — where there’s this shared resource, but there’s this race to catch everything,” he said.
Ruttenberg urged clammers to follow fishing regulations so the mollusks have the chance to grow.
Cal Poly students research clam population
Pismo clams can live up to 50 years if they dodge hungry seabirds and clammers.
Due to their lack of neural centers, however, the shellfish can’t store memories of their long lives.
Even if the clams can’t remember Cal Poly graduate student Marissa Bills, they’ve left a lasting impression on her — and she’s been delighted to watch them grow during the past five years, she said.
While completing her master’s degree in biology, Bills has led quarterly surveys at three Pismo Beach sites to measure and count the clams.
“I literally do feel like I got to watch these clams grow up,” she said.
Bills and her team of undergraduate researchers schedule surveys for the lowest tide of the season — allowing them to count clams far into the intertidal zone, where the land meets the sea.
Bills has a slightly different team for each survey, as students volunteer to participate.
On May 29, the researchers arrived at the beach near sunrise.
Bills and her team dug three trenches from the top of the wet sand into the intertidal zone. From there, the students shoveled sand into garden carts, which were wheeled into the ocean.
The cart acts like a giant sieve. When a wave crashes on the cart, the sand filters through small holes in the bottom, leaving a layer of clams.
Students then measure the width of each clam before reburying it in the sand.
“It’s quite a labor-intensive process,” Bills said.
During her recent visit to Pismo Beach, she fished a 9-millimeter-long clam out of the sand. It looked like a shiny, brown bead in her palm.
A student then walked over to show her a 5-inch-long clam — an example of what the baby clam could look like if it has the chance to grow.
“It’s just, like, a fantastic time to be a scientist studying this,” she said.
The center has been studying the clams for 10 years, which Bills called a “baby data set.” Researchers need to collect a few more years of data to be confident about trends.
“We’re really excited about the momentum that we’re building here,” she said. “Hopefully all of this research will help us better understand them and how to keep their populations healthy and happy on Pismo Beach.”
SLO County has long history of clamming
Pismo Beach has historically been considered the clam capital of the world, according to Mike James, Pismo Beach’s assistant city manager.
The legendary mollusk is featured on local storefronts and city murals, sometimes sporting a smile, sunglasses and a surfboard.
In the early 1900s, the large clams were at the center of a booming commercial and recreational fishery, according to the city of Pismo Beach’s website.
At the time, clammers would gather bucket after bucket of Pismo clams, reaping a mass of mollusks that is “beyond comprehension nowadays,” the city said.
Ultimately, a lack of regulation combined with overharvesting led to the shutdown of Pismo Beach’s commercial fishery in 1947.
Recreational clamming continued for nearly 50 more years, but the activity petered out as legal-sized clams became increasingly difficult to find.
Pismo clams had “virtually disappeared” from local shores by 1993, according to the city.
“The over-popularity of clamming resulted in losing a lot of clams because everybody was clamming,” James said. “That really prompted a deeper dive into figuring out, okay, how do we and what can we do to be able to help encourage and foster the repopulation of the clams in the clam community.”
Legal-sized clams return to Pismo Beach
In 2021, thousands of baby Pismo clams showed up on the beach in the largest recruitment pulse, or, group, the Cal Poly Center for Coastal Marine Sciences had seen.
Those 2021 clams likely haven’t reached legal size yet, she said.
Bills started seeing legal-sized clams in population surveys about two years ago, and their numbers have steadily increased, she said.
Her colleagues suspect that those clams may have belonged to the 2014 recruitment pulse, but they aren’t certain.
In 2025, they’ve continued to count legal-sized clams in their surveys, which may belong to the 2018 recruitment pulse, Ruttenberg said.
However, researchers don’t know why the mollusks have rebounded, Bills and Ruttenberg said.
Clams spawn externally, which means the females and males release their sperm and eggs into the sand simultaneously. Their decision to spawn is driven by a cue in the environment that researchers haven’t yet detected, Ruttenberg said.
The eggs are likely fertilized in the water column. Then the larvae drift in the open water to feed on phytoplankton and single-celled algae for an unknown amount of time, he said.
Finally, the baby clams settle into the sand on the beach.
“That’s basically where they’re going to live for the rest of their lives,” Ruttenberg said.
Ruttenberg said he’s concerned that the current cohort of legal-sized clams aren’t reproducing at a high enough rate to maintain a healthy adult population.
Research suggests that Pismo clams start reproducing when they’re about 1 inch long. As they grow, the shellfish are able to produce more babies.
The 2021 recruitment pulse should be large enough to reproduce, but population surveys haven’t yet detected a strong resurgence of babies, he said.
“At some point they’re going to reach legal size,” Ruttenberg said. “If fishing pressure stays really high, then what could happen is that these cohorts could simply get fished out before we have the conditions that are right for them to repopulate.”
Hundreds of clammers return to Pismo Beach
As clammers start to trickle back to Pismo Beach, James said the city’s focus is on ensuring the clam population remains stable and sustainable.
“We don’t want to get back into the same situation where we over-clammed and there just weren’t clams left in the environment anymore,” he said.
During extreme low tide events, up to 200 people per day haul buckets and measuring devices down to Pismo Beach to dig for the area’s most iconic mollusk.
While on a camping and clamming trip on May 29, Arroyo Grande resident Edwin Cardoza said he was happy to return to a hobby he shared with his dad and brother as a kid.
Cardoza said his childhood activity was put on pause when the local clam population died out decades ago.
“Only in the last three to five years have the clams really come back,” he said.
He said the Pismo clam population has “exploded,” showing up in the kinds of numbers he remembered when he was young.
Now Cardoza comes out during low tides to catch his legal limit of 10 clams, which usually take him about 30 to 45 minutes to find, he told The Tribune.
Afterwards, he grills the clams over a campfire and adds a dash of Tabasco for a hit of spice.
If he’s feeling fancy, he douses the clams in flour and fries them up like calamari. The end product is a little chewy, rich in flavor and worth the effort, Cardoza said.
A throng of clammers have returned to Pismo Beach in recent years, according to Brian Owens, a supervisor for the Northern Invertebrate Fisheries Project at the California Department of Fish and Wildlife.
On average, about 100 clammers appear on the shore per day to catch clams during low tide events, according to department surveys.
When clams began to reach legal size a few years ago, Owens’ team developed a new protocol to monitor clammers and learn more about the Pismo clams’ resurging population.
Once or twice a month, when clamming conditions are best, the team surveys clammers from the Pismo Beach pier all the way down past the 2-mile marker, Owens said.
They count how many people are out clamming, conduct checks on the size of the captured clams and ask clammers how long it took them to seize their 10 legal-size clams.
“Those three things, hopefully, will tell us the state of the fishery moving forward,” he said.
If fishers start struggling to find clams, it could be a warning sign the population is dwindling once again, Owens said.
For now, the Pismo clam is thriving with about 70% of clammers consistently harvesting their legal limits, according to fish and wildlife surveys.
“Our numbers haven’t shown any decline” in the clam population, Owens said.
How can California stop clam poaching in Pismo Beach?
As clammers start to trickle back to Pismo Beach, James said the city of Pismo Beach’s focus is on ensuring the clam population remains stable and sustainable.
“We don’t want to get back into the same situation where we over-clammed and there just weren’t clams left in the environment anymore,” he said.
Poachers present a very real threat to the future of the Pismo clam, according to California Department of Fish and Wildlife Lt. Matthew Gil.
Prior to the population’s resurrection, clam poaching had disappeared for the better part of 30 years, Gil said.
As Pismo clams begin to pop up on the beach again, however, so do those looking to illegally catch the mollusks.
“It’s a natural resource, so there’s always potential for it to be poached or taken unlawfully,” Gil said, “and we’ve definitely seen that since (the clams have) come back in the last several years.”
Since 2020, Gil’s team has issued 1,050 citations for clamming violations — commonly citing people for clamming without a fishing license or a measuring device, taking under-size clams, grabbing more than the legal limit or failing to rebury the mollusks.
Illegal clamming can result in heavy fines ranging from $100 to $1,000, according to the city of Pismo Beach.
To prevent overfishing, the fish and wildlife department has initiated a “multi-pronged approach,” including enforcement, outreach and monitoring, Gil said.
Wildlife officers patrol Pismo Beach around extreme low tides to catch people who are clamming illegally.
Some sit out in cars — up to a quarter mile away from the beach — monitoring clammers with cameras and binoculars to make sure if they’re following the law.
Officers take videos for evidence if actions are particularly egregious, Gil said.
The team also implements undercover patrols and uses license plate readers to track down people who have reportedly broken clamming laws.
“It can be very hard to kind of keep eyes on everybody,” Gil said. “So we’ll throw some officers that are undercover that are just clamming right amongst everybody else and no one has a clue.”
By the end of April, wildlife officers had seized 2,125 under-sized clams and handed out 80 citations so far this year, according to Gil.
Beyond enforcement, his team is working to educate people about the rules and regulations around clamming as well. In conjunction with California State Parks, they’ve been putting up posters, pamphlets and signage at the pier and beach entrances.
What are SLO County rules for legally harvesting clams?
In San Luis Obispo County, a person can only harvest 10 Pismo clams a day, and they must be at least 4.5 inches wide.
Each clammer must also have a valid fishing license and an accurate measuring device, and they can only harvest clams from half an hour before sunrise to half an hour after sunset.
People must also bring a clam fork, a caliper and a bucket of seawater per person.
If clammers dig up a clam that’s too small, you must rebury the mollusk immediately.
The process involves digging a small, 2-inch deep hole in the wet sand where the water will reach it. You 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, and bury the clam 6 to 8 inches deep in the sand.
If you see someone poaching clams, call the CalTip line at 888-334-2258.
“A lot of locals have taken ownership of the clam resurgence” by reporting poachers, Gil said.
Clams are an essential part of the sandy beach ecosystem, Ruttenberg said.
Otters and sea birds eat them, and they filter the water.
The clams pull in water and filter out phytoplankton and algae for food, then spit the water back out cleaner than it was before.
“They’re so iconic,” he said. “It’s really important for us to maintain this species as part of this ecosystem.”
This story was originally published June 15, 2025 at 5:00 AM with the headline "Legal-sized Pismo clams are back on SLO County beaches. Are they here to stay?."
