State concludes that Natural causes appear to be reason for deaths of estimated 2 million small fish; bay water temperature rapidly dropped below tolerance threshold for fish species involved
BALTIMORE (January 5, 2011) - The Maryland Department of the Environment is investigating a recent fish kill in the Chesapeake Bay in which an estimated two million fish have died.
Natural causes appear to be the reason for the deaths of the fish. Cold water stress exacerbated by a large population of the affected species (juvenile spot fish) appears to be the cause of the kill.
Preliminary monitoring results show that water quality in the area appears to be acceptable. Additional water quality monitoring results are to be analyzed.
The affected fish are almost exclusively juvenile spot fish, three-to-six inches in length. MDE first received reports of dead fish last week. The fish kill appears to be centered on the bay from the Bay Bridge to Poplar Island.
Spot may have difficulty surviving in colder temperatures, and the species susceptibility to winter kills is well-documented. A rapid drop in water temperatures apparently caused cold water stress. Surface water temperatures in the bay have reached about 0.5 degrees Celsius according to Md. Department of Natural Resources Bay Program monitoring data, which is the coldest December recording in 25 years of monitoring.
Adult spot normally leave the bay during winter, but juveniles occasionally winter over in the area. Bottom water temperatures near their lower thermal limit (4 to 5 degrees Celsius) are not uncommon in the bay during winter. Juvenile spot, overwintering because of a mild early winter, may be susceptible to fish kills due to sudden decreases in water temperature.
A recent DNR survey showed a very strong population of spot in the Bay this year. An increased juvenile population and limited deep water habitat would likely compound the affects of cold water stress.
Large winter kills of spot have occurred at least twice before in Maryland. In late January 1976, records show that about 15 million spot died of winter stress in the bay. A smaller number died in January 1980. Maryland experiences still smaller fish kills caused by cold water stress every few years.
MDEs investigation into the fish kill continues. The Agency continues to determine the magnitude of the kill and to obtain additional fish tissue samples. MDE works closely with DNR to investigate fish kills. In the coming days, both are to analyze DNR water quality monitoring data from recent weeks in the area of the fish kill.
Anyone who touches dead fish should take precautions such as washing hands. Residents can bury dead fish, but the tides, wildlife and natural decomposition should dispose of the fish.
MDE is asking anyone with information on fish kills to call 1-866-MDE-GOTO.
Source: Maryland Department of the Environment
More information on fish kills in Maryland