Low levels of lesions on fish, no
Pfiesteria tests yet this season
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.
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 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.