Pfiesteria present in
tributaries with healthy fish observed
July 10, 2000
This is the second biweekly report for 2000.
Weather and Water Quality
After two years of weather dominated by drought in
the region, rainfall has increased this spring and flows
into the Bay have followed a pattern of near average
conditions since March. Data from stations in Maryland's
Chesapeake Bay Monitoring Program, some coincident with the intensive Pfiesteria monitoring sites such as those on lower Eastern Shore rivers, show salinity above average for most lower tributary reaches during the winter but approaching average conditions for the summer.
Continuous water quality monitoring stations are in place through the EMPACT program (Environmental Monitoring for Public Access and Community Teaching) at three sites on the Pocomoke River in the region of the 1997 fish kill; a fourth station will soon be running on the Chicamacomico River where fish health events have been recorded in previous years. River conditions for the Shelltown area during June show water temperatures heating up to near 30 degrees C (about 86 degrees F); dissolved oxygen levels have been stable or slowly declining between June 11 and June 21 at all three Pocomoke sites (Shelltown, Cedar Hall Wharf and Rehobeth) to levels typically considered stressful for warmwater fish (below 5 mg/L).
Pfiesteria and Other Algae
Water samples have been collected since January and surveyed for Pfiesteria using a genetic probe developed by Dr. Oldach (University of Maryland
Biological Institute). Rivers sampled from January to July 2000 have included the Patuxent, Rhode, Potomac, and Middle on the western shore of the Bay, the Chicamacomico, Transquaking, Manokin, Big Annemessex, Choptank, Pocomoke, and Nanticoke Rivers as well as Tangier Sound on the Lower Eastern Shore, and Trappe Creek and the St. Martin River in the coastal bays. Of the 302 samples tested between January 17 and June 29, six samples have tested positive for Pfiesteria piscicida (Table 1). The genetic probe does not differentiate between toxic and non-toxic Pfiesteria and there has been no evidence of toxic Pfiesteria at any of these locations this year.
Table 1. Positive Pfiesteria piscicida samples during 2000. (Sampling period: January 17-June 29, n=302)
|Date of sample
||May 17 and June 1
||June 6 and June 20
The positive Pfiesteria piscicida result for a water column sample collected on June 15th on the Big Annemessex is the first monitoring record of the dinoflagellate being found in this river system. A second species of Pfiesteria, recently named by Drs. Glasgow and Burkholder (North Carolina State University) and known as
Pfiesteria shumwayae, was previously recorded in its non-toxic state from this river from a sediment sample collected in 1998.
Compared to 1999 in the month of May, chlorophyll levels, an indicator of how much algae is in the water, tended to be higher in 2000 for most of the rivers monitored on the lower Eastern Shore including the
Big Annemessex (see below), Chicamacomico (see below), Wicomico
(see below), Pocomoke (see below) and Manokin (see below). With more normal rainfall in 2000 versus the drought of 1999, more nutrients are likely to have been flushed into the rivers and, in turn, resulted in higher levels of algal biomass this year around the Bay. Data on nutrient levels at the monitoring sites during spring 2000 are not yet available.
Fish populations are being sampled across Maryland's Chesapeake and Coastal Bays by the MD Fisheries Service and the Resource Assessment Service. Among the fisheries programs reporting in, there have been more than 60,000 fish sampled between April 8 and June 27 of which more than 39,000 were menhaden. Samples collected from trawls, seines, cast nets, fyke nets and pound nets have found a less than 1.0% incidence of external anomalies this year.
During June, we have recorded four water samples that were positive for Pfiesteria piscicida (Table 1) . Four menhaden showed anomalies out of 42 collected on the Pocomoke River when Pfiesteria piscicida was recorded on June 1; however, the fish were captured in Pocomoke Sound and the positive Pfiesteria sample was collected upstream in Marumsco Creek, a tributary to the Pocomoke River. All fish for a variety of species have appeared healthy during additional sampling on the Pocomoke River through June 27. Thirteen fish (6 spot and 7 menhaden) were collected at the site that tested positive for Pfiesteria in the Big Annemessex on June 15th; all fish appeared healthy and had no lesions. Similarly, two positive Pfiesteria samples were recorded on the Transquaking/Chicamacomico system. The catch of 17 species and more than 1000 fish from Fishing Bay and the Chicamacomico River from June 6th to June 16th also appeared healthy with the exception of one white catfish that had a gill parasite.