Nantucket Sound Shellfish Opening 'A Moving Target'

By: Tim Wood

Topics: Commercial fishing and shellfishing

Shellfish Constable Renee Gagne, left, and Shellfish Constable Suzanne Phillips secure bags of oysters in the water near Old Mill Boatyard. The bags are tagged with signs warning that the oysters are in a contaminated area. TIM WOOD PHOTO

CHATHAM – Shellfish Warden Renee Gagne had a problem.

AmeriCorps volunteers recently culled oysters grown out in the town's upwelling system to ready them to be distributed in various waterways. Then a potentially toxic algae bloom closed all of Nantucket Sound, including the various inlets and embayments throughout town, to shellfishing. At almost the same time, work began on renovations to Old Mill Boatyard, including the upwelling system, which had to be shut down.

Gagne decided to gather up the 120 half-bushel bags of oysters and place them in cages in the water just seaward of the Old Mill Boatyard parking area. On Monday, the 10 cages sat in the shallow water at low tide with large “Contaminated Area, No Shellfishing” signs affixed to them.

“Our plans were thwarted,” Gagne said of the department's usual process of broadcasting the oysters at various times after the season opens on Oct. 1. Some of the 120,000 oysters grown out in the upweller were distributed; the rest have to wait in the cages until the shellfishing closure is lifted.

When that will happen remains uncertain.

Officials said last week that the Nantucket Sound closure is likely to remain in place until at least Nov. 1, and even that date is speculative, said Michael Hickey, shellfish program manager at the state division of marine fisheries.

“It's a moving target,” he said Tuesday.

All of Nantucket Sound was closed to shellfishing on Oct. 10 after the discovery of a phytoplankton bloom, which could potentially cause toxins to build up in filter-feeding shellfish like clams and oysters. Hickey said tests on samples taken last week confirmed the presence of the type of pseudo-nitzschia algae that causes the toxins, but there were no toxins present in shellfish meats that were tested.

Samples were taken again on Monday and early Tuesday and sent to labs in Gloucester and Florida, where an expert has to use an electron microscope and DNA analysis to identify the specific species of pseudo-nitzschia that causes the toxin. Before the Sound can be reopened to shellfishing, there must be two – preferably three, Hickey said – clean samples taken over a period of 10 to 14 days.

Luckily for Chatham's dozens of commercial shellfishermen, the easternmost limit of the closure is the southern tip of Morris Island, leaving the town's most productive resource areas – the Southway, Outermost Harbor and all of Chatham Harbor – still open to harvesting. Many other areas, including Oyster Pond, were already under seasonal closures.

The phytoplankton bloom is unlike anything officials have seen here before, and has also cause widespread shellfish closures in Rhode Island and Maine. Unlike Red Tide, which thrives in warmer water, this species likes cooler waters, Hickey said, and the algae tends to release more toxins as it dissipates.

And the toxin, called domoic acid, is particularly nasty. High concentrations of the toxin can cause amnesic shellfish poisoning (ASP). Symptoms include vomiting, cramps, diarrhea and incapacitating headaches, confusion, disorientation and permanent loss of short-term memory. Severe symptoms could also include seizures, coma and even death.

To date no illnesses have been reported from the current outbreak.

Because there are more than a dozen species of pseudo-nitzschia, seven of which produce toxins – four high levels of toxins – it has been difficult to isolate the algae involved in the bloom, requiring help from labs in Maine and Florida, as well as participation by the state's shellfish lab in Gloucester. There was no way to test shellfish meats locally until DEP received testing kits from Canada last week.

“There's been a learning curve here,” said Hickey. “We've never really had any experience dealing with pseudo-nitzschia.” Officials want to avoid mistakes made in other areas; in Rhode Island, Hickey said, some areas were opened after the cell counts in the bloom dropped, but had to be closed again when the levels rose.

Cells counts have gone up and down, and were showing signs of coming down in areas at the eastern end of the Sound. But because those levels can fluctuate, so tests may just be a snapshot. Hickey said officials are relying more on actual tests of the shellfish themselves.

“Ordinarily you want to look at shellfish,” he said.

Obtaining clean tests over a 10- to 14-day period allows time for the shellfish to purge themselves of the toxin. “They take the toxin up quickly and they get rid of it quickly,” Hickey said.

Gagne said scallop season will open as scheduled on Nov. 1. The adductor muscle of the scallop, the round part that is eaten, does not accumulate the toxins like the meats of clams and oysters.

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