Shellfishing reopened in all areas of the Island at noon on Monday, Oct. 31. According to the Division of Marine Fisheries (DMF), concentrations of the toxin domoic acid, which was associated with a bloom of the diatom Pseudo-nitzchia had declined to safe levels in local waters. Domoic acid causes amnesic shellfish poisoning (ASP), which can lead to neurological damage.
David Grunden of the Oak Bluffs shellfish department told The Times on Monday that he and his staff have been sending meat samples from quahogs and oysters every four days since the shellfishing was closed on Oct. 7 (in Buzzards Bay; all waters south of Cape Cod were closed after Oct. 9). He sent the most recent sample last week. The DMF also samples toxin levels in the phytoplankton in the water column, but collects those samples from their own boats, according to Mr. Grunden.
Quahogs and oysters are tested mostly because they are easier to collect than steamers and blue mussels, Mr. Grunden said. He is not aware of any significant difference in accumulation of the toxin among the different shellfish species.
This contrasts with the case of paralytic shellfish poisoning (PSP), which is caused by saxitoxin that accumulates in dinoflagellates (particularly the genus Alexandrium), another member of the phytoplankton community. Mr. Grunden said that this toxin accumulates more rapidly in blue mussels, so they are tested preferentially during PSP outbreaks.
As far Mr. Grunden was aware, this was the first ASP outbreak in Massachusetts, although events have occurred farther north. He said that he finds Pseudo-nitzschia in about 70 percent of local samples that he examines, but — until now — only in low concentrations.
He said there were two other algal blooms this summer, one in June and one in August, both involving different species of phytoplankton.
Shellfishermen did not lose much fishing, Mr. Grunden said, because the state allowed bay scalloping to continue during the closure. The toxin collects in the gut of the shellfish and not in the muscles. Generally only the muscles of scallops and conches are eaten, so their harvest was allowed to continue.
Mr. Grunden said that some people do eat the guts of bay scallops, but he doesn’t recommend it, certainly not during a shellfish closure for ASP.
Shellfishermen have been notified of the end of the ban by the removal of all signs along the shoreline, lowering of the flag at Sengekontacket Pond, and a notice at the town websites, oakbluffsma.gov; aquinnah-ma.gov; chilmarkma.gov; edgartown-ma.us; tisburyma.gov; and westtisbury-ma.gov.