Fish Health events continue in Maryland Bays, no toxic Pfiesteria has been found.
September 8, 2000
This is the sixth biweekly report for 2000.
Localized fish health events continue to be observed in areas of the lower Eastern Shore of the Chesapeake Bay and Coastal Bays. Most fish collected (representing a diversity of species) appear healthy and the recent events are mainly related to menhaden. Maryland Department of Natural Resources, in cooperation with Maryland Department of the Environment and University of Maryland Biotechnology Institute, has examined many waters in the Bay region this year. Rapid response testing of waters has identified sites on the lower Eastern Shore where Pfiesteria has been present (Figure 1 below),
but many areas have tested negative (see Figure 2, below).
Below are detailed summaries of river systems under heightened investigation due to fish health events; these systems continue to be monitored for fish health, water quality and Pfiesteria testing.
Fish Health and Pfiesteria
Table 1. History of sampling results for Ayer Creek: Menhaden catch with ulcers and Pfiesteria testing results: July and August 2000
Pfiesteria piscicida was identified as active in the water column and menhaden with ulcers were found during 5 of 5 sampling events between July 24 and August 3. Pfiesteria shumwayae has been found on one occasion (July 31). Menhaden with ulcers have been found during all sampling events but Pfiesteria piscicida has not been identified in water samples collected on the last 8 occasions between August 7 and August 28.
Marshall Creek, Newport Bay watershed - Menhaden with ulcers were found during sampling events on August 17, 21 and 24. Water samples collected on August 17 and 21 were negative for Pfiesteria, but samples from August 24 were positive for Pfiesteria piscicida. The event region was identified on August 7and continues to be monitored each week (Table 2).
Table 2. History of sampling results for Marshall Creek: Menhaden catch with ulcers and Pfiesteria testing results: August 2000.
Table 3. History of sampling results for Wetipquin Creek: Menhaden catch with ulcers and Pfiesteria testing results: August 2000.
Pokata Creek at Fishing Bay - On August 25, 37 of 85 menhaden collected had ulcers. No Pfiesteria was identified from water samples collected at the site. Pfiesteria piscicida and ulcerated menhaden have been previously identified at the site between August 2 and 15 (Table 4).
Table 4. History of sampling results at Pokata Creek: Menhaden catch with ulcers and Pfiesteria testing results: August 2000.
Pocomoke River - Four species totaling 365 fish were collected on August 15. No menhaden were collected in the samples and all fish appeared healthy. On August 22, 799 fish represented by 16 species were collected; 1 juvenile spot had an anomaly and the remaining 798 fish, including a single menhaden, appeared healthy. There is no evidence of Pfiesteria in the water column in the region at this time.
Greenwood Creek - Sampling on August 18 found 31 of 220 menhaden (5.9%) collected with ulcers. No Pfiesteria was identified from water samples collected from the site.
Wallace Creek, Honga River - Sampling was conducted on August 23 and 24. No fish were caught on August 23 and 12 of 25 (48%) menhaden collected on August 24 had ulcers. Water samples collected at the site each day tested negative for Pfiesteria, although water samples collected the previous week associated with ulcerated menhaden were positive for Pfiesteria.
St. Mary's Creek, Potomac River basin - On August 22, 25 of 103 (24.3%) menhaden collected had ulcers. Water samples collected tested negative for Pfiesteria. The site was first investigated and ulcered menhaden recorded on August 10; Pfiesteria has not been found in water samples collected from the site.
Shiles Creek, Wicomico River, Eastern Shore - Fish sampling was conducted at the mouth of Shiles Creek on August 17; 2 of 2 menhaden collected had ulcers. Water samples collected at the site tested negative for Pfiesteria.
Baywide - More than 164,000 fish have been examined during the fish health monitoring program through the Chesapeake Bay and Coastal Bays. Overall percentage of fish observed with anomalies (sores, ulcers, lesions, tumors, etc.) remains below 1% with local summer season events having >1% affected fish described previously in this and earlier reports.
Real-time environmental monitoring using fish.
The fish monitoring system includes 8 fish in individual tanks with water flowing through the tanks from a source. A test of the system was conducted at Dr. Burkholder's lab (North Carolina State University - NCSU). The figure below shows the response of the fish monitoring system to water from toxic Pfiesteria cultures in Dr. Burkholder's lab. The green line represents times when the group of 8 fish does not show significant stress. When the line turns yellow, significant stress responses are occurring with at least 6 out of the 8 fish in the group responding. Red indicates the number of fish that are severely stressed or dead.
The next figure below shows the responses for the fish monitoring system from August 7-21, 2000 on the Chicamacomico River. For most of the two-week period, the on-line group of fish was not showing significant stress to the water quality conditions. On the 13 and 14 of August, the fish group became stressed due to a water quality change associated with rain events. Previous rain events did not cause the group of fish to show significant stress. The fish then recovered and there was no additional significant stress to the fish to the end of the two-week period. One fish did become severely stressed by the end of the two-week period and later identified to be dead. The fish events on the 13 and 14 of August signaled an automated water sampler to pull river water samples during the stress events. Follow-up testing of the water samples by Dr. Oldach's lab at University of Maryland Biotechnology Institute was negative for Pfiesteria using the Pfiesteria gene probe. The stress event at the Chicamacomico River, although significant, was not severe enough to cause the whole group to remain severely stressed or die as did the exposure to water from toxic-Pfiesteria cultures at NCSU.
Routine Pfiesteria sampling
Weather, Water Flow and Water Quality
Water quality conditions for August at the Nanticoke River monitoring sites typically show 1-3 ppt lower salinity now than at the same time in 1998 or 1999. Dissolved oxygen levels are at or above stressful levels and tending to follow the seasonal patterns of the past 3 years. On the lower Pocomoke River, dissolved oxygen conditions near Shelltown are at stressful but not severely hypoxic conditions; downstream in Pocomoke Sound, dissolved oxygen levels are similar to values in previous three years. For Williams Point, oxygen conditions are near or above a healthy level of 5 mg O2/L. Salinity levels in the lower Pocomoke follow the pattern of those in the Nanticoke and are as much as 10 ppt lower than the first week of August in 1997, 1998 and 1999.
Continuous water quality monitoring stations are in place through the EMPACT program (Environmental Monitoring for Public Access and Community Teaching) at three sites on the Pocomoke River in the region of the 1997 fish kill; a fourth station is recording data on the Chicamacomico River where fish health events have been recorded in previous years. River conditions for the Shelltown area during late August show water temperatures near 25 oC (about 80 oF); dissolved oxygen levels in late August are improving from hypoxic levels earlier in the month but are being influenced by higher salinity water moving into the area. At the freshwater or very low salinity stations (Cedar Hall Wharf and Rehobeth), hypoxic conditions persist (less than or equal to 3 mg O2/L). Such levels are often considered stressful to warmwater fish under elevated temperatures. As water temperatures decline, the oxygen saturation can be expected to improve which will benefit the fish in the area. This regional pattern in water quality between the upstream freshwater sites and the downstream reach has been observed since 1997. Such patterns in dissolved oxygen distribution may have implications for keeping menhaden and other species of fish in the lower river by reducing access to these upstream areas.
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