Thursday, July 30, 2009

Native oysters return to Chesapeake

[Image courtesy of Dave Schulte, Russ Burke, and Rom Lipcius]

Science magazine reports that a team of researchers has successfully restored populations of native oysters to the Chesapeake Bay, an estuary off the Atlantic Ocean surrounded by Maryland and Virginia. This re-established metapopulation – consisting of spatially separated individual populations – is the largest of any native oyster metapopulation worldwide. The study indicates that similar recovery efforts could be successful elsewhere as well.

Over-fishing and habitat destruction have collapsed native oyster populations worldwide, and in the Chesapeake Bay, populations of native oysters had plummeted to about 1 percent of historical levels. In 2004, David Schulte and colleagues constructed different types of native oyster reefs (high-relief and low-relief) on about 86.5 acres (35 hectares) of river bed in nine protected sanctuaries throughout the Great Wicomico River in Virginia.

Schulte and his team found the height of the reef above the river bed to be the key feature of restoration – with high-relief reefs flourishing and low-relief reefs struggling. In fact, oyster density on the high-relief reefs was five times greater than on the low-relief reefs. Generally, the low-relief reefs have been the construction method of choice by fishery management agencies in the region, but these results demonstrate that high-relief reefs are much more successful at restoring native oyster populations there.

By 2007, the metapopulation of the nine separate reefs consisted of about 185 million adult and juvenile oysters – nearly the total of all oysters in Maryland waters, which is estimated at 200 million.

The researchers say that their restored populations of native oysters are still thriving. This research appears in the July 30 2009 issue of Science Express.

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