Menhaden with lesions in the
July 19, 2000
This is the third biweekly report for 2000.
Fish and Fish Health
As of July 9, more than 125,000 fish have been examined during fish health monitoring throughout the Chesapeake and Coastal Bays. Menhaden have comprised over 53,000 of the fish in the total catch. Overall percentage of fish with anomalies has remained less than 1%. Local summer season sampling events having greater than 1% affected fish have been limited to the lower Pocomoke River and Pocomoke Sound this year.
In the spring of 2000, some very young menhaden (post larval stage) in the Pocomoke River/Sound again showed similar anomalies to fish examined in 1999. Tissue of affected fish is being examined microscopically by pathologists. The presence of Kudoa-like spores associated with a myxosporidian parasite have been observed in the affected muscle of some of these fish. Histopathological examinations are continuing on fish collected more recently and the affected fish are infected with an invasive plasmodia similar to what was observed in menhaden during 1999. Fish from other tributaries have not been observed with external anomalies, however, a sampling of fish will be selected from field collections on other systems and submitted for more extensive examination in the laboratory.
Experimental studies with menhaden are also underway to try and better understand how ulcers develop and progress in the fish. Live menhaden (some with anomalies) were collected from the Pocomoke River on May 11, 2000 and brought to Horn Point Lab. On May 29, 2000 the fish were separated according the lesion severity, counted and placed in separate tanks for observation. Samples for histological examination were taken on May 29th and June 30th. Gross observations indicated rather remarkably that all external lesions seen earlier had healed, with very little mortality. Histology results are pending. John Jacobs at the Horn Point Laboratory is also maintaining a captive population of young-of-the-year Atlantic menhaden (1000+), and age 1+ fish (500+) for future research.
A reminder - please report fish kills, sick fish or fish with lesions to the Maryland Fish Health Hotline at 1-888-584-3110.
Pfiesteria and other Algae.
Weather, Water Flow and Water Quality
In the Pocomoke River, most physical water quality parameters are similar to previous years for this time of season with the exception of salinity. Salinity levels have tended to be lower this summer than 1999. Recent salinity measurements are the lowest on record for our intensive monitoring stations during the last three years in the river (see graphs below).
USGS monitoring station located on Nassawango Creek in the Pocomoke Basin in mid-July shows water levels 3-5 times greater than the 49 year historical median levels. Precipitation on the lower Maryland shore has been well above average recently (see map below)
Precipitation data from http://marfchp1.met.psu.edu/Maps
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 and early July show water temperatures heating up to near 30 oC (about 86 Fo); dissolved oxygen levels in June fluctuated around 5-6 mg/L until the end of the month. The preliminary data set shows dissolved oxygen concentrations dropped below 2.5 mg/L on July 1 then quickly recovered to levels at or above 5 mg/L in the following days. Around the time of dissolved oxygen event, turbidity doubled on two occasions; once on June 29 and again on July 1, with temperature, pH and salinity also declining for a short period of time. Rain-water is naturally acidic and the pattern of events shown in the data are likely connected to rain and runoff in the region.
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