Extensive sampling of mussels has confirmed that shellfish-borne toxins are at safe or undetectable levels at all locations in the state. In California, no PSP illnesses have been reported since 1991, and no human illnesses from domoic acid poisoning have ever been reported. The annual mussel quarantine is issued for the entire California coastline every year from May 1 through Oct. 31. Commercial shellfish harvesters in California must be certified by the state and are subjected to stringent sample testing for toxins.
Commercial harvesting is stopped immediately if a potentially dangerous level of toxin is found.
PSP toxins have been detected at low to high levels in shellfish from 13 of California's 15 coastal counties ranging from Del Norte to Orange during 1998. Obispo and Santa Barbara counties. The highest concentrations of PSP toxins were detected in mussels from several locations in Marin County during the beginning of May. PSP toxicity was detected with uncommon frequency along the Santa Barbara coast between April and August. These toxins reached the highest concentrations in Santa Barbara in more than 10 years. A volunteer-based program of phytoplankton monitors assisted department biologists in detecting and managing a toxic bloom of the diatom responsible for domoic acid toxicity in Monterey Bay and along the San Luis Obispo coast during May and June, respectively.