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Creating Crab Farms on Freshwater Farm Ponds

written by: Edna •edited by: Niki Fears•updated: 11/10/2008

Watermen living on the Chesapeake Bay used to make their living harvesting oysters in the winter months and blue crabs from Memorial Weekend to Labor Day. Oysters were almost wiped out in the 1980's and blue crab harvests have declined also. New research efforts may help revive the crab industry.

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    The Infamous Blue Crab

    People have loved the blue crab for many years. It provided the crabbing industry with a steady income for many years, and introduced many tourists and vacationers to the Chesapeake area. Eating blue crab and soft shell crab has been part of the east coast culture and tradition for many seafood lovers.

    In 1993, the combined harvest of the blue crabs was valued at around 100 million U.S. dollars. Over the years the harvests of the blue crab dropped; in 2000 the combined harvest was around 45 million dollars. Since then the Department of Natural Resources has attempted to protect the blue crab to increase its numbers again. But it may be too late for the Blue crab, too.

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    What happened to the Chesapeake Bay?

    The Chesapeake Bay is the largest estuary in the US and covers 64,299 miles. It flows through parts of six states: New York, Delaware, Pennsylvania, Maryland, Virginia and West Virginia. More than 150 rivers and streams drain into the Bay. Chesepiooc is from the Native American Algonquian language, and is believed to mean "Great Shellfish Bay."

    The Cheapeake used to be one of the most fertile breeding grounds in the world, providing food for human and non human entiies living in and around the bay. Over the years, the bay has been consistently less productive. Water pollution and soil runoff from development throughout a watershed that is home to 10 million people are the main culprits. Excess nutrients wash into the Chesapeake, cause algae blooms and choke the native plant life that crabs rely on for food and habitat. In the summer, large areas of the Chesapeake contain so little oxygen that scientists call them "dead zones," because there are few, if any, marine life that can live there.

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    Raising Blue Crabs in Freshwater

    Researchers at North Carolina State University may have found a solution. Dr. Dave Eggleston, director of North Carolina State's Center for Marine Sciences and Technology (CMAST) and professor of marine, earth and atmospheric sciences, looked at various methods for helping the population recover. He found a potential solution that reduces pressure on existing crab populations, and also benefits farmers looking to diversify their crops: using irrigation ponds on farms to grow blue crabs.

    "We started out by catching small crabs in the wild and stocking them into farm ponds loaded with bass and bluegill predators, and were still able to get 12 percent survival," Eggleston says. "So we teamed with the University of Maryland's Center of Marine Biotechnology who had the expertise to growth hatchery-reared blue crabs, and stocked these blue crabs in freshwater experimental aquaculture ponds at North Carolina State's Vernon James Research and Extension Center in Plymouth, N.C., where the crabs exhibited some of the highest growth rates on record."

    The critical piece was to see if crabs could live in irrigation ponds that are mostly freshwater. Eggleston and his researchers discovered that crabs can tolerate a salinity level of only .3 parts per thousand, about the same level found in coastal tap water. They next researched the best set of circumstances for raising crab: population density, food rations, and habitat structure in ponds.

    This past July, Eggleston and Ray Harris, North Carolina State director of cooperative extension for Carteret County, conducted a large-scale test where they stocked a 10-acre lake with 40,000 hatchery-raised crabs, and a smaller pond with 4,000 crabs. The crabs take roughly 105 days to reach maturity and so far the endeavor looks successful. Eggleston expects that in a given year, a farm could produce two to three harvests, since crabs don't do well in freshwater during the winter months.

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    Resources for reading

    http://www.cbsnews.com/stories/2008/07/16/tech/main4265867.shtml?source=search_story

    http://en.wikipedia.org/wiki/Chesapeake_Bay