Something is killing an unusual number of manatees in Everglades National Park, and Florida wildlife officials aren't sure what it is.

"A number of dead manatees have recently been reported in the park. Necropsies are inconclusive, but biologists are considering environmental factors such as red tide and cold weather," said a Facebook post from the park.

Four bodies have been recovered, but nine manatee deaths have been reported in the park, the Miami Herald reported. Cold weather was cited as the cause in two of the deaths, but biologists have yet to learn what killed the other two.

Michelle Kerr, a spokeswoman for the Fish and Wildlife Research Institute, told the Herald the bodies have been found in remote locations that make it more difficult to determine the cause of death.

As of Feb. 8, 101 manatee deaths have been recorded in Florida.

Last year, the total number of manatee deaths in the state was 824, figures from the Florida Fish and Wildlife Conservation Commission show. Red tide was blamed for 144 deaths. The toxic algae bloom was suspected in another 71 deaths.

The state experienced one of its largest and longest red tides on record last year. It lasted from October 2017 until this past November. Hundreds of marine mammals, including dolphins and whales, were killed along with tons of fish and dozens of sea turtles.

The manatee deaths are occurring at the same time a rare Bryde's whale carcass was found in the Everglades. The 38-foot young adult male weighed more than 23,000 pounds, the park service said.

After a necropsy, the whale carcass was loaded on a truck and taken to Fort DeSoto Park at the mouth of Tampa Bay. The whale has been buried there. Later this year, the skeleton and skull will be dug up and taken to the Smithsonian Institution, the Tampa Bay Times reported.