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.
The record for total manatee deaths was 830 in 2013. The previous record for manatee deaths caused by boat strikes was 97 in 2009.
According to state records, the five-year average for manatee deaths annually is 490, with 79 caused by boats.