MIAMI - Wildlife officials say 520 manatees died in Florida last year, including a record 104 killed by boat strikes. According to Florida Fish and Wildlife Conservation Commission data released Thursday, cold stress killed 23 of the protected sea cows in 2016. Eighty-eight manatees died of natural causes, while 150 deaths remained undetermined. Surveys last February counted 6,250 manatees, the most since those counts started in 1991. Due to the rising manatee population, the U.S. Fish and Wildlife Service has proposed designating the species as threatened, rather than endangered...