Updated September 28, 2010: Shortly after this blog went to press, the U.S. Environmental Protection Agency announced draft regulations (click here for additional detail) requiring the jurisdictions in the Chesapeake Bay watershed to impose more stringent curbs on nitrogen, phosphorous and sediment pollution.

The proposed rules would affect Delaware, the District of Columbia, Maryland, New York, Pennsylvania, Virginia and West Virginia. The EPA action is intended to improve the Chesapeake's water quality and its status as a habitat for fish and shellfish.

On Maryland's Eastern Shore, the future of the seafood business is intertwined with the ecosystem of the Chesapeake Bay.

According to Maryland's Department of Agriculture, the estimated value of Maryland's seafood industry is $700 million, and the bay provides a livelihood to some 6,600 watermen.

Oystering is a key aspect of the bay's heritage -- the early Native Americans called the bay "great shellfish growing water." But the Chesapeake's heritage of abundance has been threatened by decades of ecological imbalance.

A cruise on the skipjack Rebecca T. Ruark (pictured right) provides a powerful lesson in the ecology of the Chesapeake Bay.

According to the state of Maryland, skipjacks are the last working boats under sail in the United States. Skipjacks originated in the 1890s to dredge for Chesapeake Bay oysters. The single-mast, double-sailed vessels were prized for their ease of construction, stability and maneuverability in the bay's shallow waters.

The Chesapeake Bay skipjack fleet, which numbered 2,000 at its peak, declined to about 80 vessels in the 1950s, By  2002 -- the year in which the fleet was designated a national historic landmark -- there were only a dozen vessels left, the oldest of which is the Rebecca Ruark.

The Rebecca Ruark is captained by Wade H. Murphy Jr. (pictured right), a third-generation Maryland waterman. A cruise with Murphy is a riveting lesson in the challenges of conserving the Chesapeake Bay and its oyster population. While some conservation measures have been successful -- the ban on the use of DDT has brought the Chesapeake's osprey and eagle populations back from the brink of extinction over the past several decades -- the oyster population has been more difficult to restore.

Murphy estimates that the Chesapeake Bay's oyster population has declined from 15 million bushels in 1886 -- the year in which the Rebecca Ruark was built -- to about 100,000 bushels in 2009. (You can do the math, as Murphy has: In just 124 years, the bay's oyster population has dropped to two-thirds of one percent of its 1886 level.)

The precipitous fall in the oyster population has been attributed to numerous causes. According to the Maryland Department of Natural Resources, un-regulated overfishing in the late 1800s and early 1900s was an initial driver, as have been outbreaks of parasitic infections in recent decades. Murphy traces the decline to three other factors: global warming, the effects of upstream dams, and the continuing discharge of pollutants into the Chesapeake Bay.

Murphy's family has been oystering in the Chesapeake Bay since the late 19th century and has observed first-hand the effects of global warming, changing salinity and pollution.

Next Page: What happens when the bay fails to freeze over.