In January 2011, The Maryland Department of the Environment began investigating a 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.
According to Maryland Department of the Environment, preliminary monitoring results showed that water quality in the area appeared to be acceptable. Additional water quality monitoring results were being analyzed.
The affected fish were almost exclusively juvenile spot fish, three-to-six inches in length. MDE first received reports of dead fish in early January. The fish kill appeared 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.
MDE has advised that 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 encourages anyone with information on fish kills to call 1-866-MDE-GOTO.