Pfiesteria found in
no evidence of toxicity
Pfiesteria Monitoring Activities:
September 7, 1999 Summary
DNRs 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 Burkholders 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
As 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.
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.
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.