Pfiesteria Monitoring Update; Carp die off in progress;
fish kills associated with Mahogany Tides in May

June 20, 2000


This is the first report on Pfiesteria-related monitoring programs in Maryland for 2000.

Weather and Water Quality 2000
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. Intensive water quality monitoring was initiated in April on nine river systems for the Pfiesteria monitoring program (Middle, Pocomoke, Manokin, Big Annemessex, Nanticoke, Wicomico, Chicamacomico/Transquaking Rivers in Chesapeake Bay and St. Martin River and Trappe Creek in the Coastal Bays). Data from stations in Marylandís 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. Salinity levels during the spring are tracking towards the long term mean in these same areas.

Water temperatures warmed significantly in many areas during March. Increased cloudiness and rainy weather through most of April brought temperatures back to normal levels in the lower 50 Foí s (approximately 11 oC) for the season. A rapid rise in air temperatures in early May brought an equally rapid, 15 Fo (8 oC) rise in water temperature to many areas of the Bay. Water temperatures in the middle of the Bay declined slightly through May but have again increased with the warmer weather in June to a normal mid-70 Foís (approximately 19 oC) for this time of year. Secchi depths and dissolved oxygen levels tend to be below the mean conditions with some significant declines during March. In at least one case, the lower Patuxent, we have found evidence of algal blooms in March that could have effectively reduced oxygen and water clarity.

Pfiesteria and Other Algae 2000
Water samples have been collected since January and surveyed for Pfiesteria using a genetic probe developed by Dr. Oldach (University of Maryland Biotechnology Institue). Rivers sampled from January to June 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 Naticoke 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 209 samples tested between January 17 and May 24, one sample tested positive for the presence of Pfiesteria piscicida on the Middle River in April (4/20/00), two on the Pocomoke River (5/17/00 and 6/1/00), and one on the Transquaking River (6/6/00). No toxic Pfiesteria has been identified to date this year.

Additional algal sampling from the Chesapeake Bay Monitoring Program this spring located regions of very high chlorophyll levels in the Bay. The regions were associated with a bloom of another dinoflagellate, Prorocentrum minimum, that resulted in many reports of mahogany tide in the mid-Bay region (get more information on this bloom.)

Fish 2000
Fish populations are being sampled across Marylandís 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 56,000 fish sampled between April 8 and June 16 of which more than 35,000 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.

One of the target species sampled is Atlantic menhaden. In May of 1999, very young menhaden collected from the Lower Eastern Shore were observed with ulcers . Histological examinations of those young menhaden concluded that ulcerated fish were infected with a myxosporidian parasite (Kudoa sp.) and some fish contained an invasive stage of a possible other species of myxozoan parasite. Additional sampling of young-of-year menhaden in 1999 showed lesioned fish from Middle River with bacterial secondary infections and possible primary infections from a fungus, Aphanomyces invadans. In 2000, young-of-year menhaden have been sampled as soon as they entered the Bay tributaries to better study how and when infections are initiated. Incidences of ulcerated menhaden on the lower Pocomoke River during mid-May through mid-June were higher than other sampling sites statewide. Sampling on May 19 found 45 of 282 menhaden with ulcers while 383 individuals of other species were normal. June 1 sampling found 4 of 42 menhaden with ulcers and 575 individuals of other species with no anomalies. Sampling on June 13 revealed no anomalies on 715 fish captured which included 90 young-of-year menhaden. Tissue samples of the affected fish have been submitted to laboratories for histological examination.

Beginning in May of 2000, a Baywide epidemic die-off of carp has been reported. Reports were from the upper tidal fresh to lower salinity reaches of many tributaries as well as some freshwater impoundments. The largest kills were in the tributaries north of the Bay Bridges. A bacterium, Flexibacter columnaris, affects the gills and may become systemic and result in death. Only adult carp are being affected, however, there are also some additional reports of catfish dying. Investigations by the Departments of Natural Resources and Environment and the University of Maryland are continuing.

A number of fish kills were also reported in conjunction with heavy blooms of mahogany tides in May. As the algal blooms respire or as the algal cells die and decay, dissolved oxygen levels may be reduced to the point that fish are unable to live. In localized bloom areas, all species of fish and blue crabs were affected.

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