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For Immediate Release
June 4, 2020


Chris Nash
(603) 568-6741

Precautionary Shellfishing Harvest Closure for Atlantic Waters

Concord, NH - To protect the public from the possible consumption of contaminated shellfish, officials from the New Hampshire Department of Environmental Services (NHDES) and the New Hampshire Fish and Game Department have closed all nearshore and offshore Atlantic waters in New Hampshire for the taking of all species of molluscan shellfish (mussels, clams, oysters) until further notice. This action is in response to very high levels of a microscopic marine algae capable of producing a neurotoxin, domoic acid, that causes Amnesic Shellfish Poisoning or ASP.


“Our routine monitoring of tidal waters for harmful types of microscopic marine algae began showing extremely high concentrations of a particular type of algae last week” said Chris Nash, Shellfish Program Manager for NHDES. “Although shellfish tested last week from several locations showed no domoic acid, the production of toxin from this type of algae is not predictable. Recent samples continue to show extremely high populations of this algae in seawater, unlike anything we have seen before in New Hampshire waters. It is important to be cautious until more shellfish testing can be done, and until the algae bloom subsides.” New samples results are expected by June 9.


Algae cell abundance measured in Hampton/Seabrook last week was over one million cells per liter of seawater. The previous high count in N.H. was 40,000 cells per liter. Concerns about domoic acid are triggered at 15,000 cells per liter. Those very high levels continue to be observed in Hampton, with even higher levels seen in offshore Atlantic waters this week. Although officials emphasize no tests have shown any domoic acid in NH shellfish, it is important to repeat the testing of shellfish tissue to assure that shellfish are fit for human consumption. The repeat testing will be done early next week.


This precautionary shellfish harvest closure does not apply to commercial or recreational harvest of oysters in Little Bay and Great Bay, where algae populations are low. Seafood consumers should note that the closure does not apply to the harvest or consumption of lobster, although state officials continue to advise consumers to avoid eating lobster tomalley, the soft green substance inside the lobster’s body. Furthermore, these algae pose no health threats to swimmers. Officials from NHDES will continue to monitor seawater algae populations and shellfish toxicity levels throughout coastal New Hampshire and will implement additional closures as appropriate. Changes to the open/closed status of shellfish waters will be announced on the Clam Flat Hotline (1-800-43-CLAMS) and on the NH Coastal Atlas (


Amnesic Shellfish Poisoning is a condition in which filter-feeding shellfish such as clams, oysters and mussels accumulate domoic acid, a neurotoxin produced by a naturally-occurring marine algae. Ingesting the toxin can cause a variety of symptoms including vomiting, nausea, diarrhea, and abdominal cramps. In more severe cases, neurological symptoms develop within 48 hours of consumption, and can include headache, dizziness, disorientation, motor weakness, seizures, cardiac arrhythmias, temporary and/or permanent short term memory loss, and possible death. Cooking or freezing does not make contaminated shellfish safe for consumption. Although New Hampshire has no documented events of ASP/domoic acid in shellfish, this toxin has been documented in several areas of the Gulf of Maine over the last few years. For more information, consult the NHDES Shellfish Program website at