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Fish kill task force evaluates results of latest study, Nov. 18, 2008

The Shenandoah River Fish Kill Task Force met Nov. 17, 2008, to review the latest research on the causes of unexplained fish kills in several Virginia river systems since 2003. Though researchers have not identified a cause, they are evaluating several significant findings and considering several theories. Theories include the possibility of multiple stressors on fish populations that make the cause of the kills more complex than a single contaminant, virus or bacteria. Fish kills mainly have affected smallmouth bass and redbreast sunfish, though the incidence of fish deaths was relatively low in 2008.

Fish kill investigation findings:

• Water quality and environmental conditions
• Analyses of passive samplers (imitation fish tissue)
• Bottom-dwelling stream life
• Fish health
• Bacteria and viruses

Water quality and environmental conditions

DEQ monitored every two weeks from March through May at multiple sites in the Shenandoah, James and Cowpasture rivers, and several comparison streams, for metals. Dr. Dan Downey of James Madison University conducted a study on the South Fork Shenandoah River and a heavily farmed tributary, Cub Run, that evaluated physical and environmental conditions, metals, nutrients, organic chemical, and pesticides. This was done at frequent intervals before, during and after storm events between March and May 2008. The fish kills have occurred mostly during the spring months, starting when water temperatures reach about 59 degrees Fahrenheit in March and April, and ending when temperatures reach the mid- to upper 70s in mid-June. Fish kills appear to be connected to spawning periods for many of the fish species that have been affected. Water quality data from these studies and from extensive sampling during previous fish kill seasons have not identified any contaminants at levels that exceed water quality criteria or known levels of concern for toxic chemicals. This monitoring does not cover every possible water quality parameter, though it does include the most likely potential contaminants.

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Analyses of passive samplers (imitation fish tissue)

Passive samplers were placed at multiple sites in the Shenandoah and Cowpasture rivers in spring 2007 by the Friends of the North Fork and DEQ. Additional samplers were deployed in spring 2008. These samplers imitate fish tissue and chemicals during a four- to six-week period and allow measurements of chemicals that are normally not detected in conventional water samples. A wide range of chemicals were detected and quantified, but no chemicals were found at levels equal to or above known water quality criteria at any sites.

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Dr. Reese Voshell of Virginia Tech led a multi-year study that evaluated invertebrate communities in the North and South Forks of the Shenandoah and a number of tributaries. Data analyses included comparisons with other large river systems, historical comparisons in the Shenandoah River, and indications whether areas with severe fish kills had corresponding harm to small creatures living on stream bottoms. None of the large river sites in the Shenandoah basin showed significant reduction in biological conditions. The health of small stream creatures showed no patterns that corresponded with areas of heavy fish kills. The data provided no evidence that toxic substances were present in amounts that would cause biological harm. In general, the presence of these creatures in the large river sections appears to be consistent with streams that have high levels of nutrients.

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Studies of fish health continued in 2008 by Dr. Vicki Blazer of the U.S. Geological Survey, and Dr. Don Orth of Virginia Tech and associates. Studies focused on fish kill areas in the Shenandoah, James and Cowpasture rivers and included comparison sites in the Rappahannock, New, North Fork Holston and other rivers. Fish were collected before, during and after fish kills. Specimens were examined externally and internally for lesions, general health and abnormalities of skin, gills and internal organs. In addition, parasites were identified and quantified, microscopic analysis was conducted on gills and internal organs, and blood chemistry was evaluated. As seen in previous years, male fish from the Shenandoah and Cowpasture rivers had a high incidence of immature female eggs in the testes, known as intersex. The studies suggest that a wide variety of parasites, bacteria and viruses caused infections in fish that died. It is not known whether fish kills and reproductive issues are linked. 

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In 2008, Dr. Rocco Cipriano of USGS conducted bacterial analyses on numerous specimens from fish kill and comparison sites before, during and after kills in the Shenandoah, James, Cowpasture and other rivers. Cultures were obtained from skin, gills and internal organs. The findings show that pre-kill fish had diverse types of bacteria, but no symptoms. Once the fish kills and symptoms such as skin lesions began, the dominant bacteria shifted to Aeromonas salmonicida. When fish kills ended in mid- to late June, the bacteria in fish from the rivers with fish kills returned to the diverse groups seen before the kills. Specimens examined from streams without fish kills did not appear to host Aeromonas salmonicida at any time, even when fish kills were occurring in other rivers. Aeromonas salmonicida causes furunculosis, a disease with symptoms consistent with those observed in dead and dying fish in the Shenandoah, Cowpasture and James rivers. However, the investigation has not determined whether the bacteria caused the fish kills or is related to them.

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