A record-topping 767 manatees died in 2010, with cold stress accounting for as many as 500 deaths, say figures released Wednesday by the Florida Fish and Wildlife Research Institute in St. Petersburg.
Last winter's cold snap killed 244 manatees, and 35 were killed by the cold in December.
Cold stress also contributed to of 21 of 96 newborn manatee deaths. Biologists say the cold probably contributed to many of the 214 deaths in the "undetermined" category and the 68 in the "unrecovered" category.
Those numbers are "of concern" to state wildlife officials, institute director Gil McRae said in a news release. He said biologists will look for ''long-term implications for the manatee population."
Because of cold-related deaths, the number of manatees killed last year is nearly double the five-year average. Pat Rose of the Save the Manatee Club said if such high losses continue, it could send manatee population into a downward spiral again.
Manatees are particularly sensitive to cold water. When the temperature drops below 68 degrees, they seek refuge in the warmer water from springs and power-plant outfalls.
Last winter's cold deaths were different from normal, said Martine deWit, who oversees the state's marine mammal pathology lab in St. Petersburg.
Normally, cold kills manatees slowly. Their skin develops lesions, their metabolism slows, and they stop eating, she said. Generally, they succumb to secondary infections. But last winter's cold spell killed manatees more quickly, she said, causing what she called "acute cold shock" — akin to severe hypothermia.
The same cold spell that killed so many manatees also produced ideal conditions for counting the number of live manatees last year. The result: a record number that topped 5,000 for the first time. That number — 5,076 — was also classified as a minimum number, meaning there could be more manatees out there that did not get counted.
Craig Pittman can be reached at firstname.lastname@example.org.