Plunging temperatures seem to have triggered the deaths of about 2 million fish in Maryland's portion of the Chesapeake Bay in an unusually large winter fish kill.

Fish kills were reported in late December and early January from the Chesapeake Bay Bridge to Tangier Sound, including sites along Poplar and Kent Islands, Calvert County and the Honga River in Dorchester County.

Most of the dead were juvenile spot, 3-6 inches in length.

Spokesman Jay Apperson of the Maryland Department of the Environment said that cold water was the likely cause of the kill. Preliminary study shows that water quality data in the area was acceptable. Further analysis of water quality data and fish tissue is expected in February.

Spot are vulnerable to rapid drops in water temperature, which reached record lows in December. The Maryland Department of Natural Resources reported surface water temperatures at just 0.5 degrees Celsius, the coldest December water temperature in 25 years.

Adult spot normally leave the Bay for the winter. But a mild early winter sometimes lures juveniles to stay for the season, and they fall victim to stress if the water grows too cold too quickly.

A recent survey by the Maryland Department of Natural Resources showed a very strong population of spot in the Bay this year. An increased juvenile population would increase competition for warmer deepwater habitat and likely compound the effects of cold water stress.

Large winter kills of spot have occurred at least twice before in Maryland. Approximately 15 million spot died of winter stress in January 1976 and a smaller number died in January 1980. Maryland experiences smaller fish kills caused by cold water stress every few years.