No new fish kills in tidewater Maryland
Pfiesteria Monitoring Activities:
On July 22, an estimated 500,000 dead menhaden were discovered in the lower Pocomoke River and Bullbegger Creek located on the Virginia side of Pocomoke Sound . The site of the kill appeared to be Bullbegger Creek with fish drifting into the Pocomoke River and Sound due to tidal and wind effects. Low numbers of dead menhaden in Bullbegger Creek were still being found as recently as August 5 according to State of Virginia authorities. Available evidence continues to suggests low dissolved oxygen conditions were responsible for the fish kills in Bullbegger Creek. To date, water samples collected from Bullbegger Creek and the Pocomoke River on July 22 and 23 are being used in fish bioassays conducted by Dr. JoAnn Burkholder (North Carolina State University), genetic testing of the algae by Dr. David Oldach (University of Maryland Biotechnology Institute) and Dr. Parke Rublee (University of North Carolina, Greensboro) and testing for Pfiesteria toxins at the NOAA Cooperative Oxford Lab (Chris Dungan). There is no evidence of toxic Pfiesteria related to the kill.
As of July 30, approximately 100,000 fish have been examined during fisheries sampling this year and low rates of anomalies on the total catch (<1.0%) continues to be observed. Over 1000 fish were collected from the Pocomoke River and its tributaries on July 30; four menhaden out of 334 collected showed minor lesions; no lesions were found on the remaining 13 species totaling 865 fish. The occurrence of lesions on menhaden in the Pocomoke region has remained low (< 1.5%) since the middle of June.
Pathological examination of menhaden collected earlier in the season from the Pocomoke, Wicomico (Eastern Shore), Chicamacomico, Nanticoke, Big Annemessex Rivers and Kings Creek on the Manokin River is continuing. Documentation and identification of an internal parasite found in small numbers of young-of-the-year menhaden in the Pocomoke River and elsewhere is progressing. Fish tissues were collected from lesioned and healthy-looking menhaden then prepared for Transmission Electron Microscopy (TEM). TEM will be used to positively identify the parasite. Although the percentage of lesions in the fish collections has declined, samples of healthy-looking menhaden will continue to be collected for more detailed analysis.
During the last two weeks of July, 6264 young-of-the-year menhaden were collected from tributaries and embayments of the Tangier Sound. Thirty-two percent (2029) of the menhaden were observed with an external parasite on their gill plates known as an isopod. The isopod is a type of crustacean. These menhaden with the isopods were collected from Chicamacomico River, Fishing Bay, Big Annemessex River, Manokin River and Kings Creek and otherwise appeared healthy.
A reminder - please report fish kills, sick fish or fish with lesions to the Maryland Fish Health Hotline at 1-888-584-3110.
Maryland DNR has been collecting regular samples at approximately 50 locations in the Chesapeake and Coastal Bays for examination by Dr. David Oldach (University of Maryland) with an experimental genetic technique designed to rapidly identify the presence of Pfiesteria piscicida. As of August 6, results had been reported for 189 water samples collected on 17 different tributaries of Chesapeake Bay and Marylands coastal bays. Two samples have been positive for Pfiesteria piscicida this year. The first was collected on June 26 in the Shelltown region of the Pocomoke River and was previously reported on July 9. More recently, a sample collected on July 28 from Transquaking Creek, a tributary to the Chicamacomico River, was also positive for Pfiesteria. This technique does not differentiate between the toxic and non-toxic forms of the organism, and the lack of distressed fish during each water sampling event strongly suggests that the test detected the presence of Pfiesteria in one of its non-toxic forms. These results are not a reason for great concern, as previous experience has already demonstrated that non-toxic Pfiesteria exists in the waters of the Lower Eastern Shore. Additional samples collected during the week of July 12 on the lower Pocomoke River were all negative for Pfiesteria.
USGS reports that flow into the Bay in July was close to the minimum flow recorded for the month of July since 1951. Stream flow at Nassawango Creek, a major tributary to the lower Pocomoke River, has been at below average levels for most of the summer based on the 49-year record, but spiked to near average levels on August 5 and 6 due to runoff from the storm.
Until precipitation increases, the drought conditions and high temperatures coupled with nutrient enriched waters may continue to worsen low dissolved oxygen problems on the Lower Eastern Shore waters and other areas around the Bay, especially smaller creeks that may be poorly flushed.
Daytime measures of dissolved oxygen were below the monthly averages for these long term, mid-channel monitoring stations in July, but remained at levels acceptable for Bay fishes in this region. On the Pocomoke River, dissolved oxygen levels in the surface waters between Pocomoke City and Pocomoke Sound have declined from April to July and have stabilized throughout most of the main river since late June. In Pocomoke Sound, dissolved oxygen levels of summer have been more variable and presently lower than spring time measures (see below).
Continuous water quality monitoring equipment is in place at 3 locations on the Pocomoke River (2 existing, 1 new) over the region of the 1997 fish kill to collect data every 15 minutes as part of EPAs Environmental Monitoring for Public Access and Community Tracking (EMPACT).
Oxygen levels in the lower Pocomoke River upstream of Shelltown at the Cedar Hall Wharf location returned to levels near 5 mg/L between July 15 and 30, with the exception of one night, on July 24, where oxygen values remained near zero for the entire night. During the last week of July, dissolved oxygen levels during the night, upstream at the Rehobeth station were commonly below 4 mg/L, with several measures below 3 mg/l. Such low oxygen levels can be lethal to fish, however, fish may also be displaced to regions of higher oxygen concentrations down river and farther out into Pocomoke Sound.
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