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Nature Notes: Oysters on the Rebound

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By Ed Robinson

Ed Robinson photo

Ed Robinson photo

No, this is not a story about oysters recovering from broken hearts. It is, however, a story of a resilient species making a quiet comeback in the cool waters around Harpswell. And if you are like me, the more oysters the better, especially with a nice dry Sancerre or Chablis at hand.

Eastern oysters (Crassostrea virginica) have been in local waters for a very long time. I’m told there is an ancient pile of American oyster shells in Ewing Narrows. Native Americans and European settlers certainly enjoyed these tasty mollusks. They are a healthy source of protein and unsaturated fats, but are high in cholesterol.

In 1949, with the support of NOAA and Maine’s Division of Marine Resources and hopes of establishing a new shellfishery, European oysters from Holland (Ostrea edulis) were introduced to Basin Cove and other sites in Maine. Other introductions occurred in 1955, 1959 and in 1961, at Merepoint Bay. Regular observations were made and by 1963 scientists concluded that these new oysters could survive and that natural reproduction was occurring. Based on this success, introductions continued through the 1970’s at Leavitt Island, Wilson Cove and Bethel Point.

Why introduce a new oyster? Chris Heinig, who was involved in the oyster business in Harpwell with a company called Intertide Corp., notes that each type of oyster has its preferences for salinity, temperature, and bedding, so they tend to self-select among available sites. As an example, European oysters can tolerate high salinity levels, but will not survive long if exposed to excessive wave action, siltation or to ice and freezing conditions at extreme low tides. A healthy population of oysters improves water quality, since they are filter feeders, capable of removing plankton and other organic particles from as much as 50 gallons of seawater per day. European oysters also are known for their crisp, almost metallic flavor. Among oyster connoisseurs, you will hear more terms for the flavor of oysters than from wine fanatics.

By 1982, commercial fisherman reported finding substantial numbers of European oysters in Quahog Bay and other parts of the state, and by 1990, over 5 million pounds of oysters were harvested in Maine. But then the bottom fell out thanks to a lethal parasite called Bonamia ostreae. By 1997, total landings in Maine had dropped to only a few hundred thousand pounds. Fortunately, a small number of oysters proved resistant to the parasite and survived in tiny, scattered populations.

Fast forward to 2013 and the European oyster is quietly making a comeback from disaster. Chris has told me of several areas in Harpswell where populations are doing well enough that locally harvested oysters were on display at Browne Trading in Portland when we visited in March. In his diving days, Chris reports finding secluded pockets of local oysters up to 14″ across, giants he estimated would weigh 10 – 12 pounds after 30 – 40 years of growth. The photo with this article shows a European oyster shell that washed up on a local beach (my lips are sealed until a raw oyster comes along!).

Chris predicts that these fine oysters will continue to flourish in local waters, since the water temperatures and water quality is ideal. With all the focus on water quality in Casco Bay, it is comforting to know that a few thousand oysters have volunteered for water purification duties with no need for care and feeding. So if you come upon a cluster of them, please leave some for the future!

June 2013