How to Avoid Shellfish Poisoning

What to Know

Paralytic Shellfish Poisoning (“red tide”)

What is paralytic shellfish poisoning? Paralytic shellfish poisoning (PSP) is a serious illness that can ruin your kayaking adventure! It is caused by eating shellfish contaminated with the dinoflagellate Alexandrium catenella that contains a toxin. When this dinoflagellate increases to high numbers, the condition is sometimes (and somewhat erroneously) referred to by kayakers as a “red tide”.

What causes unsafe levels of PSP? The amount of toxin increases when water conditions are favorable. However, the exact combination of conditions that cause “blooms” of poison-producing plankton is not known. Unlike bacterial contaminants like Vibrio, warm water does not necessarily increase the level.

If the water looks dirty or red, does that mean that shellfish are contaminated? No. PSP is rarely associated with a red tinge to the water. Reddish water is more commonly associated with non-toxic organisms.

If the water is not red, does that mean that shellfish are not contaminated? No. PSP can be present in large amounts even if the water beneath your kayak looks clear. Also, the toxin can remain in shellfish long after the algae bloom is over.

Can a kayaker tell if it’s safe to gather shellfish by how they look? No, shellfish containing toxic levels of PSP don’t look or taste any different from non-toxic shellfish.

Which seafood can transmit PSP to kayak adventurers who harvest from the tidelands? All molluscan shellfish including clams, mussels, oysters, geoduck and scallops can have paralytic shellfish poison. Moon snails and other gastropods also can become toxic. Other marine species, such as sea cucumbers, might also be affected. Crabmeat is not known to contain the PSP toxin, but the guts can contain unsafe levels. To be safe, clean crab thoroughly and discard the guts.

What are the symptoms of PSP? Early symptoms include tingling of the lips and tongue, which may begin within minutes of eating poisonous shellfish or may take an hour or two to develop. Depending upon the amount of toxin a person has ingested, symptoms may progress to tingling of fingers and toes and then loss of control of arms and legs, followed by difficulty in breathing. Some kayakers have experienced a sense of floating or nausea. If a person consumes enough poison, muscles of the chest and abdomen become paralyzed. Death can result in as little as two hours, as muscles used for breathing become paralyzed.

Who is most at risk? Anyone on a kayak tour who eats PSP contaminated shellfish is at risk for illness or death.

How do I know that restaurant shellfish do not have high levels of PSP? Restaurants and stores must purchase shellfish from certified growers. Certified growers are required to have their products regularly tested for PSP. Much of the shellfish sold in Friday Harbor and the San Juan Islands is raised in Westcott Bay where toxins have never been found despite rigorous and frequent testing.


What is domoic acid? Domoic acid is a naturally occurring toxin produced by microscopic algae, specifically the diatom species Pseudo-nitzschia. Shellfish and crab ingest this algae, where the toxin concentrates. Significant amounts of domoic acid can cause Amnesic Shellfish Poisoning (ASP). ASP is transmitted by eating contaminated molluscan shellfish and crab.

Beware of any seal or sea lion behaving strangely. Humans are not the only predators affected. Sea lions and seals can become dangerous when severely affected by ASP. A few poisoned sea lions have wandered onto trafficked roads and beaches popular for kayak tours in the San Juan Islands.

How long has domoic acid been a problem? In the fall of 1991, domoic acid was detected in razor clams off the coast of Washington. In that same year, DOH began monitoring all major shellfish growing areas for domoic acid.

Is domoic acid present in all seafood? Unsafe levels of domoic acid have been detected in razor clams and Dungeness crab in Washington coastal waters. Domoic acid has also been found in bivalves in Puget Sound areas. Obviously, anyone kayaking in Washington’s San Juan Islands and elsewhere in the Salish Sea must be alert to the hazard.

Razor clams accumulate domoic acid in the edible tissue (foot, siphon and mantle) and are slow to rid themselves of the toxin. In Dungeness crab, domoic acid primarily accumulates in the viscera (also known as the gut or “butter”).

What are the symptoms of ASP? Symptoms include vomiting, nausea, diarrhea and abdominal cramps within 24 hours of ingestion. In more severe cases, neurological symptoms develop within 48 hours and include headache, dizziness, confusion, disorientation, loss of short-term memory, motor weakness, seizures, profuse respiratory secretions, cardiac arrhythmias, coma and possibly death. Short term memory loss is permanent, thus the name Amnesic Shellfish Poisoning.

General Information for Both Kinds of Shellfish Poisoning

Does cooking the shellfish make it safe to eat? No. The poison is not destroyed by cooking or freezing.

What should I do if I think someone I am kayaking with may have PSP or ASP? If symptoms are mild, call your health care provider and your local public health agency. If symptoms are severe, call 911 or transport the affected person to the emergency room. There is no antidote for either.

What is the treatment? There is no medication available. The only treatment for severe cases of PSP is the use of a mechanical respirator and oxygen. Severe cases of ASP result in permanent short-term memory loss and worse.

How can I protect myself and fellow kayakers from PSP and ASP? Prevention is the only protection. Before harvesting any kind of shellfish on your kayaking adventure, check the marine Biotoxin Bulletin or call the Marine Biotoxin Hotline at 360-236-3330 to find out what recreational kayaking areas are closed to harvest due to PSP. Do not expect beaches to be marked with a sign. For all species, always check https://fortress.wa.gov/doh/biotoxin/biotoxin.html

Other Illnesses Associated with Shellfish

Some people have allergic reactions to shellfish and in severe cases this can lead to anaphalactic shock with difficulty in breathing which can require medical attention.

Raw shellfish present other risks. Vibrio bacteria can cause gastro-intestinal illness similar to flu. Certain viruses can cause hepatitis and other illnesses. All of these are easily prevented by thoroughly cooking the shellfish.

To Obtain More Information before your Kayaking Adventure

Call the Washington State Department of Health’s Office of Shellfish and Water Protection at (360) 236-3330 or the Marine Biotoxin Hotline at 1-800-562-5632 before your kayaking adventure in Washington.

In addition to checking the status of Biotoxin closures, seekers of razor clams and crabs heed:
• For razor clams: the Washington State Department of Fish & Wildlife periodically opens recreational razor clam seasons (Fish & Wildlife website), and does so only after DOH testing shows domoic acid to be at safe levels. Razor clam harvest is allowed only on days and in areas officially opened by Fish & Wildlife.
• For Dungeness crab: check Fish and Wildlife crab harvest seasons and be sure to clean the crab thoroughly, removing all viscera.