In Northumberland County, parts of 38 waterways are restricted for the harvesting of shellfish (oysters, clams, mussels and scallops). Other counties in the Northern Neck are similarly affected (Westmoreland - 25, Lancaster 24, Richmond 4). The restrictions are due to high concentrations of fecal coliform bacteria, and they do not apply to the harvesting of either finfish or crabs, or to recreational use of the water. Shellfish restrictions are also the reason for the formal “impairment” of these waterways by the EPA (www.epa.gov/owow/tmdl).
The Shellfish Sanitation Division of the Virginia Department of Health takes systematic monthly samples in all our waterways. The samples are analyzed for fecal coliform bacteria, an indicator species of contamination. Data for the most recent 30 months are compiled for each station, and analyzed statistically to emphasize the importance of very high values. If the result from each station exceeds 14 bacterial colonies (actually, a measure called MPN, or “Most Probable Number”) per 100 ml of water (about a cup), then restrictions are imposed, and continually adjusted if the data change. 14-bacteria/100 ml is an extremely strict standard, which is necessary because filter-feeding oysters are often eaten raw, perhaps long after, and far from where they were harvested. Over many days, especially if the live oyster is not kept cold, bacteria can multiply. We don’t want people to get sick from eating Virginia oysters on the half-shell!
The accompanying map of the Little Wicomico River shows 19 of the 26 sampling stations for the western part of that waterway. The boundaries between restricted and unrestricted waters as of May 1999 are also shown. The boundary in Cod Creek was adjusted southward about 1000 feet in April of 2001. The number plotted at each sampling station is the statistically “averaged” bacterial concentration as of October 1999. Note that the restricted areas are located in the headwaters of the river. This is true of all our waterways, demonstrating that the bacterial contamination is probably coming from the land, not from the Bay or from the Potomac River. The salinity, or salt content, of the water in all our creeks decreases toward the headwaters of the creek because of groundwater discharge and runoff, which mixes with saltier water from the Bay or the Potomac.
We know that fecal coliform bacteria come from vertebrate animals, but which ones? There is considerable research underway at present, using several biochemical techniques (BST, or Bacterial Source Tracking) to try to identify the animals responsible, and NAPS has helped collect samples. Current thinking implicates wildlife like raccoons and birds that forage (and defecate) on or near the water as being the primary culprits. Although failed septic systems cannot be dismissed, the fact that so few people live in the headwaters of most of the creeks, suggests that humans are not the primary cause of the contamination. If wildlife can be demonstrated to be the primary source of bacteria, there is little we can do about it. We will just have to accept this “impairment” as being a natural process, and shift our attention to reducing the nutrification of our creeks and the Bay. Nutrification is an impairment that we can address. We should, of course, always be sure our septic systems are properly maintained. This means minimizing the solids and water that go down the drain, not pouring strong chemicals down the drain and inspecting the septic tank every 3 years to see if it needs pumping. Also, we can try to keep feces from our pets out of the water.
Restrictions on the harvesting of shellfish should not discourage oyster gardeners from growing oysters in restricted waters. Oysters can be eaten legally if they are “cleansed” or “relayed” by being transferred to unrestricted water, which is easily accomplished if the oysters are already in floats. The oysters can always be used as “seed” on natural oyster grounds or artificial reefs, of course. Because oysters are filter feeders, their very presence in the creeks helps to clarify the water, as well as to increase the concentration of spat which helps re-seed local, natural reefs. The Shellfish Sanitation Division in White Stone (435-1095) can answer your questions about shellfish restrictions.