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For Immediate Release
August 9, 2019


Chris Nash, NHDES Shellfish Program
(603) 568-6741

Atlantic Coast Reopened for Shellfish Harvest

Concord, NH – The New Hampshire Department of Environmental Services (NHDES) and the New Hampshire Fish and Game Department (NHFG) announce that effective today the ban on harvest of shellfish due to “red tide” is lifted for all species of shellfish except surf clams. The harvest closure went into effect on May 9, 2019, for the Atlantic Ocean and Hampton/Seabrook Harbor, in response to elevated levels of Paralytic Shellfish Poisoning or PSP, commonly known as “red tide,” detected in blue mussels collected from Hampton/Seabrook Harbor and from Gosport Harbor, Isles of Shoals. The harvest closure was later extended to Great Bay and Little Bay on June 28.  


“Red tide toxicity levels have been steadily decreasing in New Hampshire shellfish,” said Chris Nash, Shellfish Program Manager for NHDES. “Populations of the microscopic marine algae that produce the toxin have been falling at all of our monitoring stations for several weeks now. As a result, toxin levels in most species of shellfish have dropped to the point where we can lift the ban on harvest. Our colleagues in Maine and Massachusetts have been reporting similar declines.”  


The one exception is that surf clams along the Atlantic Coast continue to show unacceptably high levels of PSP toxin.   


“Different species of shellfish rid themselves of the toxin at different rates,” Nash explained. “Surf clams typically retain the toxin much longer than other types of shellfish, such as blue mussels, softshell clams and oysters.”    


In New Hampshire, surf clams are primarily harvested recreationally, not commercially. The next round of surf clam testing is scheduled for late August/early September.   


A precautionary harvest closure affecting Great Bay and Little Bay was implemented on June 28, when blue mussels from the area showed toxicity levels just below the mandatory closure threshold of 80 micrograms of toxin per 100 grams of shellfish tissue. Oysters collected at the same time from the commercial shellfish farms of Little Bay showed very low levels of toxin, but were subject to the precautionary closure to allow for additional testing. Those test results led to the lifting of the June 28 Great Bay/Little Bay closure on July 1. Intensive testing of shellfish tissue and monitoring of marine algae populations since that time has documented that conditions have remained stable. 


Nash cautioned that the red tide issue is not necessarily gone for the year. “The marine algae that causes PSP can sometimes show a second bloom in late summer or fall. Furthermore, there are other species of marine algae that become active later in the summer, fall, and even into the winter months,” he said. “These algae can cause syndromes such as Amnesic Shellfish Poisoning, Diarrhetic Shellfish Poisoning, and other issues, so we need to be vigilant in monitoring our ocean and estuarine waters.” 


Officials from NHDES will continue to monitor seawater algae populations and shellfish toxicity levels throughout coastal New Hampshire. 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 ( 


Although the red tide harvest closure is being lifted, NHDES and NHFG remind residents that the recreational harvest season for both softshell clams and oysters remains closed. Weather permitting, recreational harvest for these species will resume when their seasons reopen in early September.   


For more information on red tide and other harmful algal blooms, consult the NHDES Shellfish Program website at 


Also see the NH Fish and Game Red Tide Resource Center at