Paralytic Shellfish Poisoning in Alaska Facts and Discussion
Commonly asked questions about PSP
How do shellfish become contaminated?
Shellfish feed by filtering small food particles, including algae, out of the water. When shellfish filter the microscopic algae that produce PSP toxins, they accumulate the toxins in their tissues. Shellfish are resistant to the PSP toxins, but can pass them on to other animals and humans that consume the shellfish.
What causes levels of PSP toxins to increase?
The level of PSP toxins is usually very low in the oceans. Occasionally, under certain weather and water conditions, algae populations can bloom (reproduce rapidly to extremely high numbers). During blooms of Alexandrium (the organism associated with PSP in Alaska) concentrations of PSP toxins become high. The algae bloom ceases when nutrients in the water are depleted and/or the environmental conditions, such as light and temperature, no longer support the growth of the algae. However, even after a bloom ends, levels of PSP toxins can remain high in certain species of shellfish for an extended period. Butter clams, for example, can retain toxins for up to two years after a bloom.
What level of PSP toxins in shellfish is too high for humans to eat?
The US Food and Drug Administration limit for PSP toxins is 80 micrograms per 100 grams of shellfish tissue.
Is there an antidote for paralytic shellfish poisoning?
No. There is no antidote for PSP. After seeking medical attention, for mild cases the only thing you can do is wait until the toxins pass through your system. In severe cases victims must be put on life support such as a ventilator until the toxins pass out of the body. Seek immediate medical attention if you or someone you know experiences PSP symptoms.
What can I do if I or someone else is suffering from PSP?
Seek medical attention. Call 911 or your health care provider immediately.
Which types of seafood pose a risk?
All recreation and subsistence harvested bivalve shellfish, including mussels, clams, geoducks, oysters, and scallops, can contain PSP toxins. Predatory snails, such as moon snails and whelks, also have been known to contain PSP toxins and should be avoided. Crab meat is not known to contain PSP toxins, but their guts can contain the toxin if they fed on contaminated shellfish. PSP toxins are water soluble, so cooking the crab with their guts can cause the toxin to exit the gut and enter the crab meat that you will consume. Before cooking crab, remove the back shell of the crab and take out the dark soft tissue that makes up the digestive system and crab butter (hepatopancreas).
Which types of seafood do not pose a risk?
Most single-shelled shellfish, such as non-predatory snails, chitons, gumboots, and abalone, are bottom forage feeders and do not accumulate PSP toxins. Sea urchins and sea cucumbers are not known to contain PSP toxins.
Shellfish bought from restaurants and stores are safe for consumption. Commercially sold bivalve shellfish are required to be tested for PSP toxins. Crab is not regularly tested for PSP toxins. Most crab sold to stores and restaurants have had their guts removed, but if you buy live crab or harvest it yourself, it is important to always remove the crab guts before cooking.
Are shellfish bought in stores or sold at restaurants safe for consumption?
Yes. The Alaska Department of Environmental Conservation ensures that shellfish you buy are safe. The clams, mussels, scallops, oysters, and geoducks you buy must be below 80 micrograms of PSP toxin per 100 grams of shellfish tissue. Restaurants and stores must buy their shellfish from certified growers, and those growers are required to have their shellfish regularly tested for PSP toxins. Crab is not regularly tested for PSP toxins. Crab meat is not known to contain PSP toxins, but their guts can contain the toxin from feeding on contaminated shellfish. Crab sold to stores and restaurants typically have had their guts removed or they are removed before cooking.
Are any beaches in Alaska safe for harvesting shellfish?
No. There is no PSP testing program set up in Alaska for recreational or subsistence harvested shellfish. Alaska also does not certify any beaches in Alaska as PSP free. Shellfish harvested on any Alaska beach has the potential to have high levels of PSP toxins.
Are some shellfish more toxic than others?
Yes. Different shellfish species differ in the rate at which they take up toxins, the level of toxins they can contain, how the toxins are distributed in their bodies, and the length of time they retain the toxins. In Alaska, butter clams and blue mussels tend to accumulate the highest levels of PSP toxins. Some shellfish species, particularly butter clams, geoducks, and scallops, tend to be toxic for longer periods of time. Littleneck clams are typically less toxic and retain their toxins for a shorter amount of time than the other species. Be aware, that does not mean they are always safe to eat—you can get PSP from littleneck clams. Also, littleneck clams and butter clams can occur on the same beach and look similar, making it important to know the difference between them.
What determines the toxicity level of a shellfish?
Many factors determine how toxic a single shellfish is. These include:
- The amount of toxic algae in the water
- The level of PSP toxins in the individual dinoflagellate alga
- Species of shellfish
- How fast and how much toxic algae the shellfish eats
- How long the shellfish retains the PSP toxins
Does cooking the shellfish eliminate the PSP toxins?
No. Biotoxins are not destroyed during cooking or freezing. Pressure cooking does not destroy the toxins. There is no way to prepare shellfish infected with PSP toxins that will make them safe to eat.
What is a “red tide”?
“Red tide” is a term used to describe an area of discolored water that is formed by an algae bloom (a rapid increase in the numbers of planktonic algae). The term “red tide” is deceiving because not all red tides are red (they can be brown, purple, pink, or amber) and it is not actually a tide. Red tides are often associated with poisonous shellfish, but not all red tides are the result of toxic algae species like the one that causes PSP, and toxic algae species do not always form a red tide.
If the water is not red does that mean the shellfish are safe to eat?
No. Although PSP can be associated with a “red tide,” it is usually not an indicator. The water may be clear when there are high levels of PSP toxins present. Nontoxic algae species also can turn the water red, meaning that shellfish can be completely safe to eat when the water is red. Also, the toxins can remain in shellfish long after the bloom has ended. The color of the water is not a good indication of the presence or absence of PSP toxins and it is dangerous to assume that the lack of a red tide means the shellfish are safe to eat.
Can I tell if it is safe to eat the shellfish by the way they look?
No. Shellfish that have high levels of PSP look no different from those that are safe to eat. The only way to identify the toxin is through laboratory testing.
Can I taste if the shellfish are toxic?
No. Shellfish containing PSP toxins do not taste, smell, or look any different from uncontaminated shellfish. The only way to identify the toxin is through laboratory testing. Using a “sample and see” method is also unreliable and dangerous. A single shellfish may contain enough PSP toxins to kill you. Even if a single shellfish doesn’t cause PSP symptoms, an entire meal may contain a dose high enough to kill.
Is it safe to harvest shellfish in months that have the letter “r”?
No. This is a misconception. PSP toxins have been detected during months that were previously thought to be safe. Algal blooms are most common during late spring and summer, but seasonal occurrences are expanding with climate change. Also, when the toxic algae are not blooming they form cysts that rest on the ocean floor until conditions are right to bloom. Shellfish are bottom-dwelling filter feeders that can still consume those toxic cysts during non-bloom periods and become toxic for human consumption. In addition, different kinds of shellfish absorb PSP toxins at different rates and retain the toxins for various amounts of time. Butter clams, for example, can retain toxins for up to two years after a bloom.
If someone else eats shellfish from a beach and doesn’t get sick, does that mean the beach is safe?
No. Do not assume a beach is safe because someone else ate shellfish from it and did not get sick. Shellfish on the same beach can have various amounts of toxins. Also, factors like body size and metabolism can influence how a person reacts to PSP toxins—one person may not get sick and another may become very ill from eating the same shellfish. As an algal bloom progresses and shellfish consume more of the toxic algae, the shellfish will become more toxic. Shellfish consumed just days apart may have considerably different levels of PSP toxins.
If one beach has shellfish that are toxin free, does that mean an adjacent beach is toxin free as well?
No. In the ocean, winds, tides, and water currents distribute the toxic algae. This can cause concentrated patches of the toxic algae and the infected shellfish. As a result, one beach may be toxin free, while the beach right next to it can contain shellfish with very high levels of PSP toxins. The patchiness of the toxic algae can even result in the same beach having some shellfish that are safe to eat and some that can make you severely ill.
Are the shellfish safe to eat if birds and other animals are eating them and don’t look sick?
No. We do not know the tolerance level for PSP toxins in most other marine organisms. Even if those animals are not getting sick, you could still become seriously ill if you consume the shellfish.
Does PSP affect other organisms?
Yes. PSP can cause symptoms in birds, fish, and marine mammals that are similar to humans. Those animals are affected by consuming zooplankton, shellfish, and/or forage fish that have the toxic algae in their systems. Our pets can suffer similar symptoms and death from consuming infected shellfish or fish off of the beach.
How can I protect myself from PSP?
- Do not eat shellfish that have been subsistence or recreationally harvested.
- Purchase shellfish from a reputable store or restaurant.
- Do not eat the viscera (guts) of crabs. Clean and eviscerate crabs before cooking.
Can I get other illnesses from consuming shellfish?
Yes. Some people are allergic to shellfish. You can also become ill from bacteria or viruses in shellfish.
What if I choose to eat subsistence or recreationally harvested shellfish despite the risks?
Eating subsistence or recreationally harvested shellfish from beaches in Alaska is dangerous. The easiest way to protect yourself is to not eat them. Bivalve shellfish sold at stores and restaurants are required to be tested for PSP toxins and are safe for human consumption. Crab is not regularly tested for PSP, but crab sold to stores and restaurants typically have had their guts removed or they are removed before cooking.
If you insist on eating recreationally harvested shellfish, there are precautions you can take to reduce your risk, but none of these steps can protect you from PSP.
- Know the recent history of PSP for the area in which you are harvesting.
- Be aware of the season of the year.
- Blooms occur more often in late spring and early summer. But understand that a bloom can occur at any time of the year.
- Be able to recognize the species you are harvesting and know their ability to
concentrate and retain PSP toxins. Some shellfish species reach higher levels
of PSP toxins and retain toxins longer than others.
- Butter clams and blue mussels are known to reach the highest concentrations of PSP toxins.
- Butter clams can retain toxins for up to two years.
- Littleneck clams usually do not reach toxicity levels as high as butter clams, and the levels typically drop off quicker. But there is no guarantee that you will not get PSP from littleneck clams. Littleneck clams and butter clams can occur on the same beach and look similar, so it is important to be able to distinguish the two species.
- Be aware: No matter how much precaution you take, there is no way to ensure that untested shellfish you harvest are free of PSP toxins.
- Crabs can accumulate the PSP toxins in their digestive system. Before cooking crab, remove the back shell and take out the dark soft tissue that makes up the digestive system and the crab butter (hepatopancreas).
- A pilot program to help local communities in shellfish monitoring was in effect through June 2015. It was started in 2012 by the Alaska Division of Environmental Health in partnership with the Alaska Department of Fish and Game and the Alaska Department of Health and Social Services. Learn about areas and beaches that are participating in the program and contact information for each of those areas.