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Restoring Oysters to Great Bay

2009 Season Update

Due to disease, pollution and harvest, historic oyster populations in the Great Bay Estuary have dramatically reduced over time.  Numbers of spawning-size oysters (at least 2.5” long) have tumbled from 225,000 in 1993 to 85,000 in 2008. Despite this troubling decline, populations have shown signs of rebound following an exceptional spawning year in 2006.

The Nature Conservancy, together with the University of New Hampshire, the National Oceanic and Atmospheric Administration, and others, is working hard to help these resilient bivalves.  Oysters filter out nutrients and suspended solids and serve as the estuary's water purification system. They also form into reefs that provide habitat and feeding grounds for estuarine fish and invertebrates.  Viable oyster populations are a critical element of Great Bay Estuary health.

In 2009, The Nature Conservancy led a community-based NH Oyster Conservationist (OC) program to produce juvenile oysters used to restore native oyster areas of Great Bay Estuary. This is the fourth year of the program started by UNH, and the second year run by TNC.  Cages with oysters were floated off 22 homeowner docks around the estuary during the summer, and volunteers monitor growth and mortality.  At the end of the season, the program collected over 3,000 healthy juveniles for use in restoring depleted oyster reefs of Great Bay.

Our destination for conservationist oysters this year was a newly constructed reef in the Oyster River in Durham.   The Oyster River has great historic significance as a prime habitat for oysters, and sadly, only a small one-acre live reef remains today.  To help this population expand, TNC and UNH constructed a new reef adjacent to the live bed using a combination of recycled oyster shells and clam shells from harvest off the Grand Banks.  The idea is to place shell near spawning oysters to provide a hard surface for larval oysters to set upon.  It’s a technique most commonly used in the mid-Atlantic area and we were eager to see how well it could work in New Hampshire.

In June 2009, the Conservancy and UNH hired a barge to cover about 8,000 square feet of tidal river bottom with 20 tons of recycled shell to create a new oyster reef.  When snorkeling down to the shell reef in October, we found reasonable numbers of young oysters set on the shell.  Sampling results showed an average of 30 live oyster spat for every 10 square feet of reef, with some deep areas of the reef being much denser.  Overall, it is estimated that the reef provided a new home for a total of about 20,000 young oysters! 

These results are especially encouraging given preliminary findings from a NH Fish and Game survey which indicate that 2009 was a lower than average year for natural spat production in the estuary.  We would reasonably expect greater number of spatfall in the next several years on this reef.  In addition, we plan to build on our successes to construct an even larger shell reef in the Oyster River in summer of 2010.  This project, together with the fantastic work of our Oyster Conservationist volunteers, will continue to help restore our native oyster to its rightful place of ecological supremacy in Great Bay!

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