Marine Invertebrates of Interest: Bivalves

clams on the sand

Overview

California's coastal waters are home to a multitude of invertebrates (species lacking a bony skeleton). A small fraction of these, including bivalves such as clams and mussels, are actually targeted by California's recreational and commercial fisheries. Read on to learn more about bivalve species identification, biology, habitat, geographic range, fishing methods, and more.

Clams

Hand holding a pismo clam

Current Status of Fisheries Reports

Past Status of Fisheries Reports

Articles, Blog Posts, and Other Resources

Pismo Clam Frequently Asked Questions

What are the recreational regulations for Pismo clams?

The regulations for recreational harvest of Pismo clams and clams in general are found on the Ocean Sport Fishing regulation webpage and in California Code of Regulations (CCR), Title 14, Sections 29.20 and 29.40

Summarized regulations as of 2024:

To harvest clams, anyone 16 years of age or older must possess a valid sport fishing license, and a Sport Ocean Enhancement Validation is required in ocean waters south of Point Arguello (Santa Barbara County). Clams may be harvested one-half hour before sunrise to one-half hour after sunset 29.20(b). Gear restrictions are listed in section 29.20(c). 

Anglers are allowed to possess a maximum of 10 Pismo clams. The minimum size is five inches in shell diameter measured at the widest part for the area north of the boundary between San Luis Obispo and Monterey counties, and four and one-half inches south of that boundary line (29.40 (c)). Pismo clams must be immediately measured, and any undersize clams shall be immediately reburied in the area from which they were taken (29.20 (d)). The proper way to rebury a Pismo clam is shown in this short video clip

Pismo clams may be taken in Santa Cruz and Monterey counties September 1 through April 30. In all other counties, Pismo clams may be taken any time of the year. No clams shall be taken within state marine reserves or other marine protected areas which prohibit the take of clams (CCR, Title 14, Section 632).

Is there commercial harvest of Pismo clams?

No, Pismo clams are not allowed to be harvested commercially. Historically, there was a commercial fishery for Pismo clams from the early 1900s through 1947. Commercial harvest was prohibited after 1947.

How is the Pismo clam population?

Pismo clam abundance has increased in recent years both locally and in other regions of southern and central California, primarily due to strong recruitment events in recent years.

How long does it take for Pismo clams to reach legal size?

Where can I go clamming for Pismo clams?

Clammers can take Pismo clams statewide, but you won’t be able to find them north of Half Moon Bay. The heart of the clam population is south of San Franscisco on the Central Coast, near Pismo Beach; and at various beaches in Santa Barbara, Ventura, Los Angeles, Orange, and San Diego counties. Please use our mobile Ocean Sport Fish Map to find out the specific regulations for your location.

Are there legal sized Pismo clams in the Pismo Beach Area?

Are there any notice signs posted about Pismo clam regulations in the Pismo Beach area?

There are several signs posted along the beach at various locations on both State Parks property and the City of Pismo Beach. The signs posted by the City of Pismo Beach are posted at walkways along the coastline and at various spots at Pismo Pier. State Parks have posted several interpretive signs about Pismo clams near the entrances to the Oceano Dunes on Grand and Pier Avenues as well as at campground areas. The Department of Fish and Wildlife posted notice signs about recreational Pismo clam regulations and some of the concerns associated with illegal harvest of undersized clams.

Why are there so many unburied Pismo clams in the Pismo Beach area?

There have been several instances over the past few years where large numbers of Pismo clams have become unburied during low tide events. These events appear to be localized and have occurred in several locations along Pismo State Beach. 

The cause of these events remains unclear. Several possibilities include harmful algal blooms that produce domoic acid, bacterial and fungal infections that degrade muscle and visceral tissue, stress from environmental changes such as temperature fluctuations, and overcrowding. In the last five years, the Pismo clam population has increased, and some unburying events are in these densely populated areas. 

The Department of Fish and Wildlife is working collaboratively with State Parks, California Department of Public Health, and researchers at California Polytechnic State University in San Luis Obispo to investigate possible causes.

Where do the Pismo Beach unburying events occur?

These large unburying events appear to happen more often between the Pismo Beach Pier and Grand Avenue. High clam concentrations mostly occur north of the Pismo Creek outlet, and this is where some of the larger unburying events have been noted. Large surfacing events have also occurred directly north of the Pismo Beach pier up to the area of the bluffs.

Do unburying events happen year round?

To date, unburying events have been observed during summer. The first of these large events reported to the Department of Fish and Wildlife and State Parks occurred in August 2020. Two additional events were reported in August 2021 and 2022, and so far, four major events have been reported for 2023. The events in 2023 began earlier in summer during June.

Have unburied clams been tested for marine biotoxins?

Samples of Pismo clams have been sent to the California Department of Fish and Wildlife’s Shellfish Health Laboratory to assess the general health of the animals, look for any abnormalities on a cellular level that may indicate recent injuries or illness, and test for the presence of known bivalve pathogens. These tests can determine whether an animal was infected prior to its death and allow researchers to determine whether an infectious agent--such as a virus, bacteria, or fungus--may be the cause of an unusual behavior or illness. While several known marine shellfish pathogens have been eliminated as the cause of this unusual unburying behavior and no obvious signs of injury or illness has been observed in the unburied clams, the health investigation is ongoing. 

Additional samples of the clam meat and viscera were sent to the California Department of Public Health to be tested for marine biotoxins—specifically domoic acid and paralytic shellfish poisoning. These naturally occurring toxins are produced by phytoplankton and can accumulate in filter-feeding shellfish, posing a public health threat for those people who consume shellfish. While trace amounts of these toxins were detected in these clams, the amounts of these toxins were well below the threshold levels that would trigger human health concerns.

To learn more about health advisories and warnings of contaminated shellfish from marine biotoxins please visit the Health Advisories website by the Department of Fish and Wildlife, and for more information about biotoxin monitoring visit the Marine Biotoxin Monitoring Program website by the Department of Public Health.

What should we do if we see people collecting unburied clams?

If you notice people collecting clams or engaging in illegal harvest activities, please report it to CalTIP (Californians Turn in Poachers and Polluters) immediately. CalTIP is a confidential reporting program that encourages the public to provide the Department of Fish and Wildlife with factual information that could lead to the arrest of poachers and polluters. 

The toll-free telephone number operates 24 hours a day, 7 days a week, and you do not have to give your name. The CalTIP number is 1-888-334-CALTIP (888 334-2258).

What causes the sand formations that Pismo clams make during certain low tides and conditions?

During some low tide conditions, Pismo clams create mounds by expelling sand from their siphons. The sand settles near the siphon holes and creates a mound that looks like a sand dollar. A common misconception is that the mounds are created from heavy vehicles driving over the clams, forcing them to unbury. This is not the case, as it has been noted in vehicle closure areas, and was previously documented in a Pismo clam paper from the 1920s.

Is there any research currently being done on Pismo clams?

Researchers at both Cal Poly and at Concordia University in Irvine, CA have been studying Pismo clams both locally and in other areas of central and southern California for the past few years. These efforts are being led by Dr. Benjamin Ruttenberg at Cal Poly and Dr. Sean Bignami at Concordia and their students who have examined aspects of their reproductive biology and population abundance. 

Three publications so far have come out of this work. The first paper dealt with reproductive aspects of Pismo clams in central and southern California and appeared in the journal Aquatic Biology(PDF). The second article provided updated information on population density and recruitment in central and southern California and appeared in the California Fish and Wildlife Scientific Journal. The third article provided an updated status of Pismo clam populations across their range in California and appeared in the journal Regional Studies in Marine Science

In addition to these Cal Poly is conducting research on several aspects regarding Pismo clams. Some of these include mark-recapture studies to track growth and movement, evaluation of spatial variation in sand grain size and its importance as habitat for Pismo clams, impacts of predation by gulls and otters, and ongoing monitoring of population abundance and size structure around Pismo Beach and Morro Bay.

Where can I find more information about Pismo clams?

For more information on Pismo clams please refer to the Department of Fish and Wildlife’s Enhanced Status Report, or view a presentation on an overview of the Pismo clam given by Department scientists and Law Enforcement staff.

Where can I find more information about public health advisories and warnings for shellfish?

To learn more about health advisories and warnings of contaminated shellfish from marine biotoxins please visit the Health Advisories website by the Department of Fish and Wildlife, and for more information about biotoxin monitoring visit the Marine Biotoxin Monitoring Program website by the Department of Public Health.

Scallops

Two scallops underwater

Current Status of Fisheries Report

None available - visit the Marine Species Portal to view other species of interest.

Past Status of Fisheries Reports

Articles, Blog Posts, and Other Resources

None available - visit the Marine Management News blog to view other posts of interest or subscribe to the latest news.

Mussels

Mussels in tidepool

Current Status of Fisheries Report

Past Status of Fisheries Reports

Articles, Blog Posts, Other Resources

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Oysters

To learn more about CDFW's management of cultured oysters, explore the Aquaculture page.

Current Status of Fisheries Report

None available - visit the Marine Species Portal to view other species of interest.

Past Status of Fisheries Reports

Articles, Blog Posts, Other Resources

None available - visit the Marine Management News blog to view other posts of interest or subscribe to the latest news.

Shellfish Health Advisory Information

Marine Region (Region 7)
Regional Manager: Dr. Craig Shuman
Main Office: 20 Lower Ragsdale Drive, Suite 100, Monterey, CA  93940
Email CDFW's Marine Region  |  (831) 649-2870
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