The tragic decline of oysters in the Chesapeake Bay to 1
percent of the population of 120 years ago is the result of pollution, two curious and only slightly understood oyster diseases and management systems in Maryland and Virginia which have not applied adequate conservation measures.
The situation has become so grave that oysters are likely to become commercially, if not biologically, extinct in the Chesapeake. A massive effort is necessary to restore both the oyster fishery and the critical role that oysters play in the Bay ecosystem.
Oysters are more than hors d'oeuvres. They are arguably the most important animal in the bay because of their effect on water quality and other organisms. Oysters grow on the bottom in large congregations called ''bars'' which, when undisturbed, will form ''reefs'' of substantial vertical elevation. Oyster reefs were an outstanding feature of the Chesapeake noted in Captain John Smith's log, but they are very rare in the bay now, having been worked down since colonial times to the flatter bar configuration.
Oyster bars, and reefs, form the basis for diverse benthic (bottom dwelling) communities of organisms including everything from worms to crabs to predatory fish. They form important habitats for a number of recreationally and commercially valuable fish species including weakfish, croaker and drum. Any fisherman will tell you the best place to fish in the bay is over an oyster bar. The decline in bay oysters has meant a decline in this important benthic habitat.
Oysters play a valuable role in improving the Chesapeake Bay's water quality at no cost to the taxpayer. It can cost from $50 to $100 million to upgrade an average sewage treatment plant to prevent nutrients from entering the bay and causing excessive algae growth. By filtering as much as 50 gallons of water a day, an oyster can remove from the water large quantities of pollutant algae, which otherwise would cloud the water and cause low oxygen levels.
A recent analysis by Roger Newell, of the Horn Point Environmental Laboratory, estimated that the population of oysters in the bay in 1870 could filter 100 times more algae than today's oysters. In another University of Maryland study, now in draft form, researchers from the Chesapeake Biological Laboratory state:
''Reductions in nutrients alone very probably will not clear up Chesapeake waters and restore their commercial and recreational productivity so long as stocks of benthic filter feeders [oysters] continue to be over exploited.''
The value of oysters clearly goes well beyond the value of the fishery alone and justifies a substantial public commitment to restoration.
Overfishing beginning in the late 1800s was instrumental in the historical decline of Chesapeake oysters. Harvests then were 15 to 20 million bushels a year bay-wide, far in excess of what the bay could sustain. The steady decline from this level during the last 100 hundred years and the failure of most management efforts have been documented by a number of prominent bay scientists, including Dexter Haven and William Hargis of the University of Maryland. In recent decades, state repletion programs had some success in stabilizing harvest -- until the outbreak of disease.
During the 1980s, oyster disease and pollution took many more oysters than watermen did. The commercial harvest of oysters declined by more than 80 percent in Maryland and by more than 90 percent in Virginia to where the bay-wide harvest is now barely half a million bushels, the lowest it has been since records have been kept.
Roger Mann and his colleagues from the Virginia Institute of Marine Science have even suggested that with Cheapeake oysters so depleted by disease, we should consider introducing a non-native species from the Pacific as a replacement.
Fisheries scientist Dr. Brian Rothschild and others from the University of Maryland take a different view and, in a paper soon to be published in the journal Science, they analyze the way oysters have been managed and recommend substantial changes.
A key question to be resolved is whether there is sufficient oyster ''broodstock,'' adult oysters which reproduce and perpetuate the population. Historically, the states have taken a laissez-faire approach to broodstock, believing that declining profits would restrain the fishery before excessive numbers of oysters were taken.
The additional mortality caused by disease and pollution, however, seems to undermine this philosophy. Although the harvest is low, the total mortality may be enough to threaten the broodstock. Some Maryland officials continue to claim there is no broodstock problem, that enough oysters still are left behind to maintain the population. This assertion contradicts a recent Maryland Governor's Commission report on oysters which, concluded:
''. . . broodstock [has] been severely depleted and must be restored if the industry is to have a significant revival.''