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July 10, 2003
Lower Eastern Shore (Eastern Bay to Choptank River) experienced widespread algal blooms; area fish kills investigated.

Algal blooms of the possibly-toxic dinoflagellate Karlodinium micrum were investigated by Maryland Department of the Environment (Table 1) and identified on the Miles River tributaries (Leeds Creek: June 14th –18th, Oak Creek: June 26th) and a tidal pond in the watershed near Oak Creek (June 15th). The Miles River empties into Eastern Bay where citizens also reported discolored waters from algal blooms on June 27th. Reports from Horn Point Laboratory researchers also indicated significant patches of algal blooms on the Choptank River on June 26th.

Several fish kills were investigated in Leeds Creek, Oak Creek and a tidal pond off the mainstem of the Miles River often associated with low dissolved oxygen (D.O.) conditions and algal blooms or post-bloom conditions. However, cell densities of K. micrum were frequently at concentrations that have been associated with toxin related fish kills in other investigations published by Center for Marine Biotechnology (COMB) researchers and co-authors Dr. Alan Place and Jon Deeds (10,000 to 30,000 cells per milliliter and above). Water samples are being tested by COMB for karlotoxin concentrations, a toxin shown to have fish killing ability (i.e. ichthyotoxicity).

Investigations by Maryland Department of the Environment, Horn Point Laboratory and Maryland DNR’s Matapeake Field Office on July 7th located thousands of dead fish over a wide area of the lower Choptank River including many adult menhaden, and a few stripers, croaker and horseshoe crabs. Fish were decaying, drifting over the river and appeared days old suggesting an environmental event that occurred before Monday with an undefined epicenter. Algal samples collected from the Tred Avon River, Trippe Creek and Peachblossom Creek, as well as the Choptank River showed low concentrations of possible harmful algal species Prorocentrum minimum or K. micrum. One live menhaden was found swimming in circles near the surface and was collected for detailed lab analyses.

Table 1. Recent investigations into fish kills and related algal bloom conditions records from water samples in the associated region.

Date Investigated Watershed Location Fish kill Algal concentrations/ml
June 14th Tred Avon River Plaindealing Creek 350 dead fish (killifish, mummichogs, silversides) Lower stretch of the creek below the fish kill 23,040 cells/ml K. micrum
June 15th Miles River Tidal pond near Royal Oak 136 dead carp, white perch and sunfish Post-bloom conditions, depleted D.O, few algal cells.
June 16th Miles River Leeds Creek 12 dead fish found near the headwaters Low D.O. at head waters, 2 miles downstream: 21,330 35, 415 cells/ml K. micrum
June 18th Miles River Leeds Creek Follow up to June 16th Low D.O. at head waters: daytime measures of 0.82 mg O2/L at bottom, 1.02 mg/L at the surface, post bloom conditions, tea-colored waters and low cell counts.
June 26th Miles River Oak Creek Est. 1000 fish Sample collected for toxin analysis found 160,000 cells/ml K. micrum.
June 26th Choptank River Choptank River None Significant concentrations of K. micrum noted in areas.
July 6-7th Eastern Bay and Choptank River including Tred Avon. Eastern Bay and Choptank River including Tred Avon. Thousands, many were menhaden but a few stripers, croaker and horseshoe crabs also dead, multiple days since the event. Low concentrations (< 212 cells/ml) of Prorocentrum or Karlodinium in samples from Tred Avon system collected 6/7. Diatoms and small flagellates found in moderate abundance.