The annual quarantine on sport-harvested mussels is normally in effect from May 1 through October 31 each year. Occasionally the annual quarantine will begin sooner than May 1 due to significant increases in toxin levels earlier in the year. Similarly, a biotoxin event may persist beyond the end of October, resulting in an extension of the annual quarantine for one or more counties. The annual mussel quarantine applies to the entire coastline of California, including all bays, inlets and harbors. The main purpose of the quarantine is to protect the public from the toxins that cause paralytic shellfish poisoning (PSP) and amnesic shellfish poisoning (ASP). Both of these syndromes are associated with consumption of bivalve (two-shelled) mollusks, such as mussels, clams, cockles, oysters and scallops, which feed by filtering tiny particles from the water. Domoic acid, the toxin responsible for ASP, has also been found at levels of concern in the viscera of crustaceans like lobster and crab and small finfish like anchovies and sardines.
The mussel quarantine restrictions and recommendations apply only to shellfish collected by sport harvesters. Mussels and other bivalve mollusks harvested by state-certified shellfish growers and sold commercially in markets and restaurants should pose no risk of poisoning to consumers. Since the PSP outbreak in 1980 included illnesses from consumption of commercially harvested oysters, commercial shellfish producers have been required to submit specimens weekly from all commercial harvest areas for PSP assay by CDPH. Bivalve mollusks imported into California are similarly monitored for biotoxins by the producer states.
Shellfish toxin levels do not rise and fall in predictable cycles and can increase rapidly. Prevention of human illnesses requires strict enforcement of the annual quarantine, combined with year-round surveillance, public education, and occasional special health advisories and commercial closures as needed.
California Department of Public Health Frequetly Asked Questions
California Department of Public Health News Release
Read more about Paralytic Shellfish Poisoning (PSP)