Fifty manatees have died from the effects of cold weather this year in Brevard County, surpassing the previous record of 28 cold weather-related deaths for all of 1990.Manatee counts in recent years show that the population has grown since 1990. Still, the deaths show how one of the coldest Florida winters in recent years continues to put a strain on sea cows."The next cold front comes before it gets a chance to warm up, and that's certainly a problem," said Andy Garrett, a biologist with the Fish and Wildlife Research Institute in St. Petersburg.The 50 manatee deaths are part of a preliminary report by the institute for Jan. 1 through Feb. 19, so the toll could rise.In Brevard and throughout the state, "cold stress syndrome," which can result in death, occurs as a result of long exposure to water temperatures below 68 degrees. The illness lasts weeks, causes manatees to stop eating and shuts down their immune systems.Researchers think many recent deaths can be attributed to the lingering effects of the syndrome, with many manatees actually affected during January's cold snap, when temperatures averaged about 16 degrees below normal."Earlier this year, the deaths were acute, but we're seeing more chronic cases of long-term illness," Garrett said.Manatees that aren't too sick and can hang on until it finally gets warm -- and stays warm -- will be able to turn themselves, feed and survive, Garrett said. But he predicted more cold-related deaths despite an eventual warming of the weather. Cold weather is keeping teams from the state's manatee rescue network busy.During a recent weekend, rescuers tried to save 10 manatees from different locations in Florida, including offshore in Indian Harbour Beach, where an adult manatee eluded rescue. That animal and others showed signs of cold stress.Other wildlife in Florida are stressed by the cold, including types of fish and sea turtles. Researchers attribute 300 sea turtle deaths in Brevard to January's cold snap.Most sea turtles recover from cold more easily compared with manatees because they don't experience long-lasting effects.Sea turtles rescued in January that survived are doing well, said Blair Witherington, a research scientist with the institute in Melbourne Beach.It becomes dangerous for turtles when the water dips below 50 degrees, which hasn't happened since the January cold snap, he said.