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Oyster Harvest

A waterman hand-tonging oysters
Hand tonging is one of many ways watermen harvest oysters. Image courtesy: Middleton Evans

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For more than a century, oysters made up one of the Bay's most valuable commercial fisheries. The interaction of over-harvesting, disease, sedimentation and poor water quality has since caused a severe decline in their numbers throughout the Chesapeake. The Bay's native oyster population is now estimated to be just 2 percent of its historical abundance.

What caused the Bay's oyster population to decline?

Scientists attribute the decline of the Bay's oyster population to a combination of several factors, including:

The decline in the Bay's native oyster population is often illustrated in terms of its impact on water quality: In the late 19th century, the native oyster population could filter a volume of water equal to that of the entire Bay every three to four days; today's depleted population takes nearly a year to filter the same volume.

How has harvest been a pressure on oysters?

Immense numbers of oysters existed in the Bay during colonial times. European settlers reported that huge oyster reefs thrusting up from the Bay's bottom posed navigational hazards to their ships. At the turn of the 20th century the Bay's oyster fishery was one of the most important in the U.S.

The Bay's oyster population has severely declined over the past century due to over-harvesting, which removed huge volumes of oysters. Over-harvesting also led to the demise of the Bay's healthy oyster reefs, which were scraped away by dredging.

Oyster beds are now usually limited to a flat, thin layer of dead shells and live oysters spread widely over the Bay's bottom. These damaged habitats:

  • Offer less surface area for oyster spat and other reef-dwelling invertebrates to attach themselves to. This impacts larger fish and blue crabs that live and breed around oyster reefs and prey upon these smaller species.
  • Are easily covered by sediment, which smothers live oysters and can eventually bury a damaged reef.

How do diseases and poor water quality affect oysters?

In addition to harvest pressure, the Bay's oysters face a number of other challenges. One of these is disease. Since the 1950s, the oyster diseases MSX and Dermo have decimated the Bay's remaining oyster population.

The Bay's oysters have also been impacted by poor water quality.

  • Changes in land use over the past century—more agricultural and urban and suburban areas and fewer forested areas—have increased the amount of nutrients and sediment that enter the Bay.
  • Excess nutrients fuel the growth of algae blooms that deplete oxygen in deeper waters and can hinder the development of oyster larvae.
  • Oysters that are under stress from poor water quality or burial by sediment are likely more prone to disease.
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Last modified: 11/02/2009
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