July 2024 Marine Biotoxin Monitoring Monthly Report

This report contains results from the California Department of Public Health (CDPH) monitoring programs for shellfish toxins and associated toxin-producing phytoplankton. Toxin concentration ranges are provided for the paralytic shellfish poisoning (PSP) toxins and for domoic acid, the latter associated with the syndrome called amnesic shellfish poisoning. Estimates are provided for the distribution and relative abundance of Alexandrium, the dinoflagellate that produces PSP toxins, and Pseudo-nitzschia, the diatom that produces domoic acid. This report also contains summary information for any quarantine or health advisory in effect during the reporting period. Finally, lists of participating agencies and volunteers for each monitoring effort are provided.

Please note the following conventions for the phytoplankton and shellfish biotoxin distribution maps:

The Marine Biotoxin Monitoring and Control Program, managed by the California Department of Public Health, is a state-wide effort involving a consortium of participating organizations, agencies, and volunteer samplers.

The phytoplankton sampling and observation element of the biotoxin monitoring program is a state-wide effort designed to detect toxin producing species of phytoplankton in ocean waters before they impact shellfish resources. The phytoplankton monitoring and observation effort can provide an advanced warning of a potential toxic bloom, allowing us to focus sampling efforts in the affected area before California's valuable shellfish resources or the public’s health is threatened.

Historically, the majority of shellfish toxicity episodes in California have originated along the open coast, occasionally moving into bays and estuaries. The shellfish sampling element of the program provides an early warning of shellfish toxicity by routinely assessing coastal resources for the presence of paralytic shellfish poisoning (PSP) toxins and domoic acid. Routine shellfish sampling is essential for protecting the public from these dangerous toxins.

For Information on Volunteering: Email  redtide@cdph.ca.gov  or call 510-412-4635

The following is a list of recent Quarantines and Health Advisories for bivalve shellfish prior to August 1, 2024. For access to current advisories, please refer to the end of this report.

● May 1, 2024, the annual mussel quarantine on sport-harvested mussels began. The quarantine applies to all species of mussels that are recreationally harvested for human consumption along the California coast, including all bays and estuaries. During the quarantine, mussels may only be harvested for use as bait. The quarantine is in place to protect the public against poisoning that can lead to serious illness, including coma and death. 

● On May 2, 2024, CDPH issued a health advisory warning consumers not to eat sport-harvested razor clams from Humboldt County due to dangerous levels of domoic acid in razor clams, which can cause Amnesic Shellfish Poisoning.

● On July 3 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Humboldt County due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.

● On July 16 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Del Norte County due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.

● On July 18 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Santa Cruz and Monterey counties due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.

● On July 19 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Sonoma County due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.

● On July 26 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Marin County due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.

 Consumers of Washington clams, also known as butter clams (Saxidomus nuttalli), are cautioned to eat only the white meat, regardless of the current quarantine status. Washington clams can concentrate the PSP toxins in the viscera and in the dark parts of the siphon and can remain toxic for a long period of time. Persons taking scallops or clams, with the exception of razor clams, are advised to remove and discard the dark parts (i.e., the digestive organs or viscera). Razor clams (Siliqua patula) are an exception to this general guidance due to their ability to concentrate and retain domoic acid in the edible white meat as well as in the viscera.

PSP toxins can produce a tingling around the mouth and fingertips within a few minutes to a few hours after eating toxic shellfish. These symptoms can be followed by disturbed balance, lack of muscular coordination, slurred speech and difficulty swallowing. In severe poisonings, complete muscular paralysis and death from asphyxiation can occur.

Symptoms of domoic acid poisoning can occur within 30 minutes to 24 hours after eating toxic seafood. In mild cases, symptoms of exposure to this nerve toxin may include vomiting, diarrhea, abdominal cramps, headache and dizziness. 

These symptoms disappear completely within several days. In severe cases, the victim may experience excessive bronchial secretions, difficulty breathing, confusion, disorientation, cardiovascular instability, seizures, permanent loss of short-term memory, coma and death.

Any person experiencing any of these symptoms should seek immediate medical care. Consumers are also advised that neither cooking or freezing eliminates domoic acid or the PSP toxins from the shellfish tissue. These toxins may also accumulate in seafood species such as crab, lobster, and small finfish like sardines and anchovies.

Sportharvesters should only collect shellfish from areas that are not affected by a current health advisory or quarantine.

Contact the “Biotoxin Information Line” at 1-800-553-4133 or view the  recreational bivalve shellfish advisory interactive map  for a current update on marine biotoxin activity prior to gathering and consuming shellfish.