Lesioned Fish on Shiles Creek
(Eastern Shore)

August 14, 1998 Update

One year to the day after last summer’s Pfiesteria outbreak on the Pocomoke River, the microorganism was back in the news.

On August 4, Maryland Department of Natural Resources (DNR) sampling crews found a small number of juvenile menhaden with fresh Pfiesteria-like lesions near the mouth of Shiles Creek, a very remote section of the lower Wicomico River on the Eastern Shore (see map below).

a 1998 map of the Wicomico River Water and Habitat Quality Monitoring Stations

To help determine the prevalence of these lesions, DNR conducted intense daily fish sampling in the area. There have been no dead fish, nor any fish acting erratically with lesions.

Overall, total numbers of menhaden samples have been very small, with only 80 menhaden found affected over a 7-day sampling period. All other fish species sampled were healthy. Due to the low numbers of fish affected, the creek and river have remained open.

Daily fish sampling has been suspended as of August 13 due to the significant decline of Pfiesteria-like lesions observed on menhaden. DNR will continue to monitor the area for visual signs of sick or dead fish through DNR’s Natural Resources Police. Fish will be sampled in the area weekly. Fish along the entire river are sampled every two weeks as part of DNR’s regular Pfiesteria monitoring activities, which began this spring.

Two of six water samples for Pfiesteria analysis taken August 5 and 6 in the area have been found to contain very low levels of what could be toxic Pfiesteria cells, per Dr. JoAnn Burkholder’s lab. The estimated levels were 130 cells per milliliter and less than 50 cells per milliliter. Species and toxicity confirmation will take several weeks.

Considering preliminary lab information together with the small numbers of menhaden found with lesions, it is possible this has been a low level, localized incidence of lesions on menhaden due to traces of toxic Pfiesteria.

This situation clearly demonstrates the value of DNR’s increased Pfiesteria-monitoring activities, a joint effort among NRP, Fisheries Service and Resource Assessment staff. All contributed to monitoring efforts, allowing investigations to begin before possible escalation of potential toxic Pfiesteria-related fish health problems.

To date, there have been no reports of Pfiesteria-related fish kills in Maryland waters this year.

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