Pfiesteria detected in the Potomac, Patapsco and Gunpowder Rivers, no evidence of toxicity

Maryland's Pfiesteria Monitoring Activities:
September 27, 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 is very sensitive, with the ability to detect just a few cells, and scientists believe high densities of Pfiesteria cells are required to harm fish.  It does not differentiate between the toxic and non-toxic forms of the organism.

Pfiesteria piscicida has recently been detected in the Potomac, Patapsco and Gunpowder Rivers in addition to detections in the Middle River system during August and September on the western shore and 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 other waters of the Chesapeake Bay.

Between September 3 and September 10, one fish kill occurred in estuarine water. The investigation revealed approximately one thousand dead, three-inch Atlantic menhaden floating in Bivalve Harbor, Wicomico County. The fish were suspected of becoming entrapped in the harbor during an episode of reduced dissolved oxygen the evening of September 9th. All of the fish appeared to have died acutely, within the same time period. Two dead fish displayed deep ulcerative lesions. Low dissolved oxygen was not confirmed, however, the harbor has an extensive history of low dissolved oxygen inducing menhaden die-offs. These events have been well documented since 1981. The previous fish kill in Bivalve Harbor occurred earlier in the year on July 16th. The dissolved oxygen levels recorded soon after this event were less than or equal to 1.0 mg/L, a level extremely stressful if not lethal to many fish species.

From April 24 through September 10, MD DNR Fisheries Service, University of Maryland Eastern Shore, and Maryland DNR Resource Assessment Service have examined 194,367 fish in 203 sample days. 74,740 of those were menhaden. Between August 28 and September 10, 5769 fish were examined; 4599 of these were menhaden. A total of 368 menhaden had ulcers and 88 had gill parasites. Lesioned menhaden have been collected from Kings Creek in the Manokin River (1 fish), Nanticoke River (5 fish), Joppatowne Creek in the Gunpowder River (35 of 50), Bird River (1 of 2), Rocky Point Creek of Back River (15 of 100), several tributaries of the Patapsco River which were Rock Creek (20 of 80), Curtis Creek (1 of 8), and Bear Creek (2 of 18), as well as Middle River. The gill parasites continue to be found on menhaden collected from the Lower Eastern Shore tributaries but the rate varies from 0% (Wicomico River, Big Annemessex) to 13% (Manokin River) of the menhaden collected at a site.

There have been 39 rapid response days. From January1 through Sept 15 the Fish Health hotline has received 194 calls. 50% were from Baltimore and A.A. counties. 25% were from the Eastern Shore.

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:
The remnant of Hurricane Floyd moved up the east coast last week and brought long awaited rain to Maryland. Flooding, however, was common. Since September 1, 6 to 12 inches of rain have fallen in areas near the Chesapeake Bay. Creek levels reached their highest level in months and in some cases, many years. Water levels in Nassawango Creek are subsiding after the peak of the storm runoff. 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. September flow into the Bay will be reported at the beginning of October.

Water Quality:
Elevated salinity levels had been associated with low river flows brought on by the drought through early September. Recent rains of 6-12 inches in the Chesapeake Bay basin from the remnants of Hurricane Floyd moved salt fronts down river and sediment loads down stream with the runoff. Water temperatures are declining from their higher than normal levels during midsummer. Dissolved oxygen conditions are improving at many Lower Eastern Shore stations.

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