Can Great Bay Oysters be Saved for a Healthier Estuary?

Jeff Barnum


Creating a new oyster reef from recycled shell. Credit: M. Latour.

In a recent blog, I discussed our work to clean up toxic stormwater pollution from the massive scrap metal facility on the banks of the Piscataqua River in Portsmouth.  One important outcome of our work was to secure funding from the operator of that facility, through EPA, for an oyster and eelgrass restoration project in the Piscataqua River.  The project, about two acres of new oyster reef and an experimental eelgrass planting, was completed this summer by The Nature Conservancy and UNH.

Why are projects like this important?  Even if you do not like to eat oysters, you have to love them.  Oysters are filter feeders, straining the water column of impurities as the tides move in and out of our estuaries. NH’s Great Bay was home to 1100 acres of healthy oyster beds in the early 1990s. Each oyster could filter 20 gallons a day, and collectively, those 1100 acres could filter the entire bay in two to three days. Today, there are only 100 acres of not-so-healthy oyster beds. Filtering the bay now takes a year and a half. Why did they disappear?

Diseases that were probably always present may have had an impact on the population already stressed by overharvest, increased pollution, and sedimentation. Recreational harvest amounts were reduced and the number of harvesters themselves dropped as the resource declined. Beds were covered with sedimentation, effectively snuffing them out. The loss of eelgrass due to nutrient loading may also be playing a role. As eelgrass disappears at an alarming rate, it no longer is present to anchor the sediment in place and to remove sediments from the water column.

In Great Bay, adult oysters typically spawn around age four which is the average size that you would buy in a restaurant or market. The fertilized spat (baby oyster) would drift in the estuary until attaching itself to a clean, hard substrate, often an existing bed. Without available substrate, the spat  would not survive. The natural spat sets (spawning events) in Great Bay were not predictable or extensive, given the small remaining population.  The future looked bleak.

Ray Grizzle of UNH’s Jackson Estuarine Lab (JEL) and Ray Konisky of The Nature Conservancy (TNC) had a plan. Why not create an artificial reef and seed it with baby oysters already attached and growing on shell? The simplified process is this: buy disease-free, fertilized spat; mix with clean shell; grow in modified cages until the oysters are dime size; and then place as a veneer on top of reefs created using more shell in locations with good flow that are not prone to siltation. TNC engages homeowners around Great Bay to grow their baby oysters in cages suspended from docks while JEL does the same in floating cages at the lab.

The reef substrate was initially hard clam shell discarded by chowder processing plants out of state. Seeing a need for more substrate, the Coastal Conservation Association of NH commenced a shell  recycling project in 2009, to collect discarded shell  from area restaurants that serve oysters. Weekly pickups of shell (over 4000 bushels to date) are transported to a location for drying to kill any potential pathogens before being placed in Great Bay prior to seeding. The collaboration not only creates new reefs, it has engaged the public to better understand the value of the estuary and its present plight to survive.  We at CLF are pleased to have played a role in obtaining funds for this year’s important project in the Piscataqua River.

While the fifteen or so acres of restored reefs, to date, pale in comparison to what has been lost, the Great Bay oyster is making a comeback. Several aquaculture projects are under way and some are now producing marketable oysters that are available locally. This is definitely encouraging.  More folks with a stake in the health of the estuary bodes well for tackling the issues of nitrogen loading, stormwater runoff, fecal coliform, and other challenges to water quality.

For more information about the Great Bay-Piscataqua Waterkeeper and my work to protect the Great Bay estuary, visit: You can also follow me on Facebook and Twitter.

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