The agency's Fish and Wildlife Research Institute documented 699 manatee deaths in state waters.
Some 244 were caused by "cold stress," exposure to low water temperatures.
The cause of death in many of the other cases was undetermined, but officials believe the cold temperatures likely contributed.
The preliminary figures indicate manatee deaths in from Jan. 1 to Dec. 5 of 2010 were nearly double the five-year average for the same time period.
The deaths were documented throughout the state and as far south as the Florida Keys.
More data will need to be collected to determine if there is a long-term effect for the population.
(Copyright 2010 by The Associated Press. All Rights Reserved.)