Annual Mussel Quarantine - Frequently Asked Questions (FAQs)
What is the
annual mussel quarantine?
The mussel quarantine is a
yearly event that happens due to dangerous levels of biotoxins that may be
present in mussels gathered by the public anywhere on the California coast,
including bays, inlets and harbors. The quarantine applies only to
sport-harvested mussels; commercially grown mussels from certified companies are
not included in the quarantine. The annual mussel quarantine is in place to
protect the public against paralytic shellfish poisoning (PSP) and domoic acid
poisoning (DAP), also known as Amnesic Shellfish Poisoning.
When is the annual mussel quarantine?
quarantine is normally in effect from May 1 through October 31. However, the
California Department of Public Health (CDPH) may begin the quarantine early, or
extend it, if monitoring results indicate the presence of dangerous levels of
biotoxins outside of the normal quarantine period. The May through October
quarantine period encompasses more than 99 percent of all PSP illnesses and
deaths reported in California since 1927.
Where is the annual mussel quarantine in effect?
The mussel quarantine is in effect from the Oregon border
to the Mexican border. All bays, inlets and harbors are included.
Why is there an annual mussel quarantine?
The annual quarantine is in place so the public does not
collect mussels during this high-risk period for marine toxins. The occurrence
of biotoxins in mussels is unpredictable and they can increase in concentration
very rapidly. Therefore, the annual quarantine period provides the best approach
for protecting the public from these potentially deadly biotoxins.
Why do these biotoxins occur at this time?
peak period for the PSP toxins probably coincides with the most desirable growth
conditions for the naturally occurring algae that produce these toxins.
These single-celled plants usually occur at very low concentrations
and pose no problems. However, when the algae "blooms" the concentration of
toxin increases dramatically. The increased amount of algae becomes a greater
food source for mussels. The more toxic algae the mussels eat, the more
biotoxins they accumulate. Biotoxins don't harm mussels, so the level in their
tissue continues to climb until the bloom subsides. When the number of
toxin-producing algal cells returns to normal low levels, the mussels eventually
flush the toxin from their systems. It can be several days to several months or
longer before they're safe to eat again.
How dangerous are PSP and DAP?
These toxins are
very dangerous and have been responsible for many deaths worldwide. Since 1903, 582 total cases including 543 illnesses and 39 deaths
have been attributed to PSP in California. Death can occur within 30 minutes of consuming toxic
There are no known antidotes to the toxins found
in mussels. Cooking does not reliably destroy the
What are the symptoms of PSP?
include tingling of the lips and tongue, which may begin within minutes of
eating toxic shellfish or may take an hour or two to develop. Symptoms may
progress to tingling of fingers and toes and then loss of control of arms and
legs, followed by difficulty in breathing. Some people feel nauseous or
experience a sense of floating. If a person consumes enough toxins, muscles of
the chest and abdomen become paralyzed, including muscles used for breathing,
and the victim can suffocate. Death from PSP has occurred in less than 30
What are the symptoms of DAP?
vomiting, nausea, diarrhea, and abdominal cramps within 24 hours of ingestion.
In severe cases, more serious symptoms develop within 48 hours and include
headache, dizziness, confusion, disorientation, loss of short-term memory,
muscle weakness, seizures, breathing difficulty, heart rhythm problems, coma and
What should I do if I think I have eaten toxic mussels?
If you think you have eaten toxic mussels and have any of
the symptoms described above, seek immediate emergency medical care at a
hospital or call 911. If any of the mussels remain, they should be refrigerated
for later testing by CDPH or another authorized laboratory.
Is it safe to eat sport-harvested mussels when the annual quarantine
is not in effect?
No, you should never assume that
sport-harvested mussels are safe to eat when the annual quarantine is not in
effect. The toxins can occur at any time, which is why CDPH continues to monitor
for them throughout the year. If dangerous levels of toxin are detected when the
quarantine is not in effect, the CDPH director and state health officer will
issue a health advisory to warn the public to avoid consuming certain seafood in
the affected areas.
The public can call the
Biotoxin Information Line 1-800-553-4133 to get updates on current quarantines
and health advisories throughout the year.
Other types of
shellfish, including oysters and clams, and commercially harvested mussels from
certified companies are not included in the quarantine.
Can I tell if the mussels along the coast are
There is no way to visibly determine if mussels or
any other seafood contain dangerous levels of these toxins. The toxins do not
affect the appearance or behavior of the shellfish in any way. The only way to
tell if the shellfish are toxic is through testing by an approved
How are the toxins detected or predicted?
maintains a year-round monitoring program for these toxins in shellfish, as well
as for the phytoplankton species that produce these toxins. This effort has been
successful thanks to the participation of many of the coastal county health
departments, State and federal agencies, and citizen volunteers who collect the
shellfish and plankton samples for analysis by scientists at the CDPH State
Public Health Laboratory in Richmond. There are currently no predictive tools
for these events, so routine monitoring of the California coastline provides the
best approach for the early detection of a toxic bloom so that the public can be
Why aren’t other shellfish, like oysters and clams, included in the
Mussels are a particularly high risk
because they can concentrate these toxins very quickly. When dangerous levels of
toxin are detected in mussels, CDPH will begin testing other shellfish species
for these toxins if samples are readily available. If samples are not easily
obtained, or if toxin levels are increasing rapidly, CDPH will issue a press
release announcing a special health advisory for the potentially toxic seafood
species in the affected area. CDPH is assisted by local county health
departments to make sure the public receives this information.
Can I eat mussels that are commercially grown during the quarantine?
Yes. Commercially grown mussels from certified companies
are exempt from this quarantine.
Why are commercially grown mussels exempt from this quarantine?
CDPH regulates all commercial bivalve shellfish growers in
the state. All of these certified companies are required to submit frequent
shellfish samples to CDPH for toxin testing. If any sample exceeds the federal
alert level for the PSP or DAP toxins, then that area is immediately closed to
harvesting until conditions become safe.
All commercial shellfish
growers in California are aquaculture operations, growing mussels, oysters and
clams from ‘seed’ that are produced in hatcheries. Aquaculture operations occur
on defined leases, making it easier to monitor and track toxin levels. There is
no commercial harvest of wild populations of shellfish permitted by CDPH in
How can I get involved with the biotoxin monitoring program?
CDPH is always interested in having new volunteers join the
shellfish and phytoplankton monitoring programs, especially if they are in an
area that needs additional coverage. Our ability to protect the
public from these dangerous toxins is due in large part to the numerous
organizations and citizen volunteers that contribute their time and effort to
provide samples to our program for testing. CDPH can provide the
necessary training and equipment for collecting and shipping samples at no cost
to the volunteer. Program participants are acknowledged in our monthly biotoxin
reports and are added to our distribution list for reports and
To learn more about volunteer opportunities, email