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Non-native oysters

The Chesapeake Bay, unlike many estuaries worldwide, has only one species of oyster, the native Eastern oyster (Crassostrea virginica). Many other estuaries also have introduced or non-native oyster species. In most cases, those non-native species were introduced intentionally to supplement or replace a native oyster species for their fisheries value from aquaculture, as wild fisheries for the native oysters failed.

Most of these introductions for aquaculture used the Pacific oyster (Crassostrea gigas). The Pacific oyster had a worldwide 2010 aquaculture production about seven times larger (by weight) that was worth about 18 times more than production from the Eastern oyster. The Pacific oyster is native to Japan and nearby waters in Asia, and the main areas where it was introduced and is being used in aquaculture are in Australia, New Zealand, Europe, and on the Pacific coast of the United States and Canada. A map of the distribution of C. gigas shows that it is on every continent except Antarctica, but does not occur on the East or Gulf Coasts of the United States.

Given the decline of the wild oyster fishery in Chesapeake Bay, and the widespread use of the Pacific oyster in other estuaries, why aren’t Pacific oysters being grown in the Chesapeake Bay? Researchers tested them in the Chesapeake Bay in the 1990s, but they did not grow well here, and were susceptible to disease. Thus, an effort was started in the late 1990s to research another Crassostrea oyster from Asia, C. ariakensis (the "Asian oyster"), as a possible replacement for the Eastern oyster. After several years of study, officials decided in 2009 not to do any further testing with this species in the Chesapeake.

More than 90% of oyster aquaculture in Virginia now uses triploid Eastern (native) oysters, which are sterile and thus grow faster and have more meat than the usual diploid oysters, and thus provide many of the benefits that were hoped for from the Asian oyster. Triploid native oysters are being used increasingly for aquaculture in Maryland as well.

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