PSP found in butter clams at Shoemaker Bay

Following up on a warning issued this summer, the risk of poisoning from area shellfish has been revised.

Shellfish specimens found around Shoemaker Bay in August had tested positive for saxitoxin, which causes paralytic shellfish poisoning (PSP). Severe cases of PSP can cause nausea, vomiting, neurological effects, respiratory failure and ultimately death. First signs tend to be a numbness of the mouth after eating tainted shellfish.

The Southeast Alaska Tribal Ocean Research website at http://www.seator.org/data maintains a page laying out updated information on beaches where toxins have been discovered. Some communities have been more greatly affected than others, such as beaches in Craig and Hydaburg. Locally, Wrangell Cooperative Association’s Indian Environmental General Assistance Program (IGAP) collects samples of mussels and clams from local beaches, which then get sent to the SEATOR laboratory in Sitka for testing. IGAP also observes water samples at its own lab, checking for signs of harmful phytoplankton.

There are primarily three types of phytoplankton which can cause harm to local residents: Alexandrium, Dinophysis, and Pseudo-nitzschia. While the phytoplankton themselves are not harmful to humans, they produce toxins which are absorbed by filter-feeders like shellfish.

Blooms of these species can put out significant amounts of toxins, which eventually get absorbed by filter-feeders like shellfish. These are not themselves harmed by the toxins, but can pass them on to humans when ingested.

Alexandrium produces saxitoxin, while Dinophysis can produce okadaic acid, which can cause non-fatal diarrhetic shellfish poisoning. Pseudo-nitzschia produces domoic acid, which can be fatal. Domoic acid in the body can lead to amnesic shellfish poisoning. Symptoms include vomiting, nausea, diarrhea, cramps and hemorrhagic gastritis. Domoic acid also damages neurons in the brain, which can cause headache, dizziness, loss of short-term memory, and at its worst seizures and cardiac arrhythmia.

So far, only saxitoxin has turned up near Wrangell, and only at the Shoemaker beach. Butter clams have been found to contain the toxin, but cockles and mussels there have been testing negative. Depending on when the blooms occurred, different species of bivalves retain toxins for different amounts of time, from months to years, which would help explain why some species do not contain saxitoxin.

An unenforced advisory to residents remains in effect, with the caveat that eating butter clams collected from the Shoemaker Bay area may have risks. IGAP staff will continue to monitor area beaches, and any new information will be updated at the SEATOR site as test results come in.