Low levels of lesions on fish, no positive
a tests yet this season

Maryland's Pfiesteria Monitoring Activities:
June 25, 1999 Summary:

In 1997, the occurrence of fish kills, fish lesion events and associated human health impacts were linked with the effects of a toxic dinoflagellate, Pfiesteria piscicida, on the Lower Eastern Shore of Maryland. The State of Maryland, through the interagency Pfiesteria Study Team and other agency and academic partners, is conducting an intensive monitoring effort to search for any signs of a toxic outbreak and to continue the evaluation of key factors that could contribute to outbreaks in the future.

The three rivers affected in 1997, the Chicamacomico River, Kings Creek and the Pocomoke River, are being monitored as well as five other systems (Nanticoke River, Wicomico River-Eastern Shore and Big Annemessex in the Chesapeake Bay and Trappe Creek and St. Martin River in the Coastal Bays) that may be susceptible to outbreaks. Water quality and fish populations are also being evaluated Bay-wide through ongoing fisheries surveys and the DNR's Chesapeake Bay Monitoring Program. The following summary updates monitoring and environmental conditions for the spring 1999 sampling season.

Weather patterns:
Despite the recent June rain events in the State, drought conditions continue in the Chesapeake Bay region this spring. USGS reports that flow into the Bay has been below average for the last 10 months and at record low flows for the month of May for the estimated total streamflow entering Chesapeake Bay). Maryland Department of the Environment issued a drought advisory for the State of Maryland in December 1998 which is still in effect. Recent rains have resulted in an increase in flow in Nassawango Creek, a tributary to the Pocomoke River, starting on June 20 recent streamflow information).

Water Quality:
Water temperatures have typically been within historical ranges for May and the beginning of June on the lower Eastern Shore. Salinity levels at the long term monitoring stations, however, are generally higher than long term averages, illustrating the influence of the extended drought and low flow conditions so far this year. Secchi depths (a measure of water clarity) and dissolved oxygen levels at these monitoring sites were typically at or below long term averages for May and early June. The latest water quality information for selected sites can be found at Eyes on the Bay!

More than 30,000 fish were collected during May and early June sampling programs of the Pfiesteria monitoring effort with low incidents of lesions (<1.0%) being observed overall. Sampling through mid-June on the Lower Eastern Shore rivers has yielded higher abundances of menhaden in 1999 when compared with 1998. On June 3, menhaden (10%, 20 of 193 fish) captured on the Pocomoke River showed signs of skin lesions and 11 fish were submitted for more detailed laboratory examination; however, none of these lesions appeared to be the type associated with Pfiesteria outbreaks in the past. Routine sampling on the lower Pocomoke found further evidence of young-of-year menhaden on June 8 (6.1%) with the same lesions as fish caught the previous week. Sixteen fish samples were taken on June 9 (sampling found 15%, 41 of 265 fish with these same lesions) and also submitted for more detailed laboratory analysis. Preliminary pathological analysis on these samples indicate the presence of a parasite. Analysis is continuing to identify the parasite, as well as examining its relationship to the fish lesions. Water samples were also collected June 9 to obtain baseline information on the algal community. Preliminary analysis found no indication of toxic Pfiesteria. Water quality parameters were within normal ranges. DNA probe results were all negative for the presence of Pfiesteria.. Additional sampling of the Pocomoke River on June 15 found much lower numbers of menhaden with lesions (1.3%, 66 of 5065 fish).

Small numbers of fish kill incidents have been reported this spring around the Bay. Fish kills have been attributed to fish becoming entrapped in shallow pools and subsequent low oxygen in the pool water, commercial or recreational fish discards in a localized area, and crab sheds that were mistaken for dead crabs. Only one kill has involved young of the year menhaden and was related to low oxygen water on the South River in early May.

Tracking of algal blooms is an important component of the monitoring program since most of the Pfiesteria outbreaks have been associated with elevated levels of algae. So far this spring, algal levels in the Pocomoke River have been highest in the vicinity of Shelltown, and, to varying extents, out in to Pocomoke Sound as well. The conditions in mid-June are similar to those in May but maximum algal levels are more narrowly concentrated in the vicinity of the mouth of the River just below Shelltown.

In addition, Dr. David Oldach (University of MD) has been examining water samples with an experimental genetic technique to search for the presence of Pfiesteria piscicida. During May, samples were collected in the eight systems listed above plus the Potomac, Patuxent and Choptank Rivers. To date this year, no water samples collected from Chesapeake Bay or the Coastal Bays have yielded positive results. This technique can be used to determine presence or absence of Pfiesteria organisms, but will not indicate whether those organisms are toxic.

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