Continued Monitoring of Shiles Creek
To date, there have been no reports of Pfiesteria-related fish kills in Maryland waters this year.
In early August, a Maryland Department of Natural Resources (DNR) fish health monitoring crew found a small number of juvenile menhaden with fresh Pfiesteria-like lesions near the mouth of Shiles Creek in a very remote section of the lower Wicomico River on the Eastern Shore (see map). All other fish species examined were healthy. There have been no dead fish in this area, nor any fish with lesions acting erratically.
DNR field crews are trained to identify possible Pfiesteria-like lesions on fish as part of the departments extensive work to monitor for signs of toxic Pfiesteria activity. The other signs are dying or dead fish with characteristic lesions, and/or fish with such lesions behaving erratically. While we sample the entire fish community, our focus is on menhaden as that is the species most frequently associated with Pfiesteria outbreaks.
Although the numbers of menhaden examined in the lower Wicomico River with lesions were very small (from a few fish to several dozen), DNR officials decided it was prudent to closely monitor the area. Fish in the area were intensively sampled for seven days. Because even smaller numbers of menhaden were observed with lesions, indicating possible decreasing prevalence, fish sampling was adjusted to a weekly schedule. The Wicomico River had already been receiving increased attention from DNR field crews through bi-weekly sampling since this spring as part of the overall monitoring plan. Additionally, DNR Natural Resources Police (NRP) officers patrol the area daily. Due to the low numbers of fish affected, the creek and river have remained open.
Large schools (thousands) of juvenile menhaden have not yet been consistently observed in the Wicomico River, nor on any other Lower Eastern Shore tributaries. Very small numbers of menhaden with fresh lesions have been observed on a sporadic basis.
DNR has also responded with increased monitoring of water and habitat quality on the Wicomico River and Shiles Creek. Water quality crews have taken water samples in the creek and river to measure standard water parameters (oxygen, salinity, temperature, pH), nutrients and algal communities, as well as water samples for Pfiesteria analysis. Standard water parameters at the site of the lesions have been typical for the region. While recent nutrient data has not yet been received from laboratories, the Wicomico River is generally representative of most Lower Eastern Shore tributaries in that it contains higher levels of nutrients -- phosphorus and nitrogen -- than similar tributaries elsewhere in the state.
Of six water samples (taken on August 5 and 6, when menhaden with lesions were initially observed) sent to Dr. JoAnn Burkholders lab in North Carolina, two showed very low levels of what could be toxic Pfiesteria-like cells. The estimated cell levels were 130 cells per milliliter (ml) and less than 50 cells per ml. To put this in perspective, Dr. Burkholder estimates that at least 100 cells per ml are necessary to cause Pfiesteria-like fish lesions. Species and toxicity confirmation will take several weeks.
Considering preliminary lab information and the small numbers of menhaden found with lesions, it is possible that a low level, localized incidence of lesions on menhaden due to traces of potentially toxic Pfiesteria has occurred.
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