Wednesday, August 22, 2012

Mashpee Using Oysters to Control Pollution

Through a friend of MOP, Curt Felix in Wellfleet, we learned of the work Richard York, the Mashpee Shellfish Constable.The following is an excerpt from a write-up on the initiative that is actively using oysters to improve water quality. 

In 2004 the town initiated an oyster aquaculture project in the Mashpee River for the purposes of restoration of the lost oyster fishery and mitigate eutrophication. Algae blooms fueled by nitrogen loading intensified to the point of creating temporary anoxic conditions causing fish and crab die-offs.

Map of the Mashpee River

Oysters can control blooms by filtering algae from the water for food. Plastic mesh bags containing very small oyster seed set on pieces of shell in the hatchery were transported to the river. After the seed grew larger, the bags were opened and the seed spread out in mesh trays for growout. More seed was stocked annually. 
Mature Oysters

Since harvests started in 2006 and a large biomass of oysters has been growing in the river, no mass fish mortalities have occurred. 

Nitrogen Removal 
The 2008 harvest of 520,000 oysters removed about 260 kilograms of nitrogen from the estuary based on analysis of oysters sampled from the river (0.5 g N/oyster). This was about 4% of the 6563 kg of nitrogen reduction needed to meet the Total Maximum Daily Load (TMDL) for nitrogen in the river requiredby the Massachusetts Department of Environmental Protection (MA DEP 2006,Report #96-TMDL-4). 

New oyster seed is purchased every year with the goal of harvesting a million oysters a year removing 500 kg of nitrogen. This would be about 8% of the reduction needed to meet the TMDL for nitrogen.

The Town uses fees from oyster licenses to fund the program.

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