August 2023 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 Health Advisories and Quarantines for bivalve shellfish prior to August 1, 2023. For access to current advisories, please refer to the end of this report.

● On August 3 CDPH lifted the domoic acid shellfish advisory related to related to sport-harvested razor clams in Humboldt County.

● On August 1 CDPH lifted the domoic acid shellfish advisory related to related to sport-harvested mussels, scallops, and clams in Santa Barbara County.

● On July 28 CDPH issued a health advisory warning consumers not to eat sport-harvested mussels, clams, or scallops from San Mateo County due to dangerous levels of the paralytic shellfish poisoning toxins in shellfish samples.

● On July 14 CDPH issued a health advisory warning consumers not to eat sport-harvested mussels, clams, or scallops from San Luis Obispo County due to dangerous levels of the paralytic shellfish poisoning toxins in shellfish samples.

● On July 6 CDPH lifted the shellfish advisory related to sport-harvested razor clams in Del Norte County. The  safety notification was issued on November 3, 2022  due to dangerous levels of naturally occurring domoic acid, also referred to as Amnesic Shellfish Poisoning. Razor clams have been continually tested and have now met the criteria for lifting the safety notification in Del Norte County. An advisory for razor clams in Humboldt County remains in effect.

On June 16 CDPH advised consumers not to eat sport-harvested mussels, clams, or scallops from Santa Barbara County due to the presence of dangerous levels of domoic acid in shellfish samples.

● On June 16 CDPH advised consumers not to eat sport-harvested mussels, clams, or scallops from Santa Barbara County due to the presence of dangerous levels of domoic acid in shellfish samples.

● On May 1 CDPH initiated the annual quarantine of sport-harvested mussels gathered along the California coast. The quarantine normally extends from May 1 through October 31, although elevated toxin levels can extend the quarantine period. This annual quarantine applies to all species of mussels that are recreationally harvested for human consumption along the California coast, including all bays and estuaries. The quarantine is in place to protect the public from poisoning that can lead to serious illness, including coma and death.

 Consumers of Washington clams, also known as butter clams (Saxidomus nuttalli), are cautioned to eat only the white meat. 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.