Pfiesteria found in Middle River,
no evidence of toxicity

Maryland's Pfiesteria Monitoring Activities:
September 7, 1999 Summary

DNR’s Resources Assessment Service has been collecting regular samples at approximately 50 locations in the Chesapeake and Coastal Bays for examination by Dr. David Oldach (University of Maryland Biotechnology Institute) with an experimental genetic technique designed to rapidly identify the presence of Pfiesteria piscicida. This sampling program is designed to determine the distribution of Pfiesteria in Maryland waters as well as alert the State to areas that may need additional surveillance. This technique does not differentiate between the toxic and non-toxic forms of the organism.

Pfiesteria piscicida has recently been detected in the Middle River system in addition to detections in the three Lower Eastern Shore river systems earlier this summer (Pocomoke River, Transquaking River and Back Creek in the Manokin River system). A number of samples are undergoing bioassays in Dr. JoAnn Burkholder’s lab (North Carolina State University) to determine if the organisms have the ability to turn toxic. Results to date indicate none of the samples were toxic. These results are not a reason for great concern, as previous experience has already demonstrated that non-toxic Pfiesteria exists in the other waters of the Chesapeake Bay.

Between August 14 and August 27, two estuarine fish kills were reported. The first appeared to be from chum discards of 10-14 inch menhaden found floating near Hoopers Island shoreline. Normal water conditions were found in the area during the investigation. A dozen fish were found dead in a second kill at the head of the Magothy River. Water quality conditions were poor with low dissolved oxygen conditions at the time of investigation and a bloom of a dinoflagellate algae known as Gyrodinium uncatenum was observed in the area. Low dissolved oxygen was considered the most probable cause of the event.

Middle Creek 1999 Menhaden lesion ratesAs of September 3, over 178,000 fish have been examined during fisheries sampling this year and low rates of anomalies on the total catch (<1.0%) continues to be observed. On August 22, however, menhaden captured from numerous creeks in the Middle River system showed a high percentage of old appearing ulcerative lesions (88%). The system has been monitored several times a week since the discovery. Observations of fresh appearing lesions have been very low since monitoring commenced and the overall lesion rate for menhaden has been about 50% and fairly stable throughout the last week. All other fish species appeared healthy. Pfiesteria was identified in most of the creeks but there has been no evidence of active toxicity.

A reminder - please report fish kills, sick fish or fish with lesions to the Maryland Fish Health Hotline at 1-888-584-3110.

Weather patterns:
More rain has fallen in the recent weeks than during the rest of the summer. USGS reports that flow into the Bay during August was about half the average flow recorded for this month since 1951 and continues to be well below average for the year. Stream flow at Nassawango Creek, a major tributary to the lower Pocomoke River, has been below average levels for most of the summer based on the 49-year record. The region recorded about 0.10 inches of rain on August 27th. Storm runoff raised the water level at the station but water levels quickly returned to below the seasonal average. Since September 1, about 0.6 inches of rain has fallen and creek levels are again on the rise.

Water Quality:
Salinity levels at the Lower Eastern Shore monitoring stations continue to rise for stations in Pocomoke River and Sound, the Manokin and Nanticoke Rivers. Elevated salinity has been associated with low river flows brought on by the drought and the salt water front continues to move upriver in lower Eastern Shore region. A recent exception to this rule has been the Chicamacomico River where measures were consistently higher than 1998 most of this year but have shown large fluctuations and lower levels in August, likely associated with localized storm events. Water temperatures are declining from their extremely high measures during midsummer. Dissolved oxygen conditions are improving at many Lower Eastern Shore stations.

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