For the first time since records began being kept in Florida in the 1970s, the number of manatee deaths in a single year has topped 800, with two weeks remaining to the end of 2013.
Numbers released by the Florida Fish and Wildlife Research Institute in St. Petersburg this week showed the number of known dead manatees at 803 as of Dec. 13. That's about 16 percent of the state's estimated population of 5,000 manatees.
And 173 of the dead were breeding-age female manatees, Martine DeWit of the institute's Marine Mammal Pathology Laboratory said Thursday.
Although it's too soon to say how this will affect the future of the species, she said, "It must have an impact to lose these important breeding females."
For comparison, last year's total number of manatee deaths was 392, which is more in line with what's normal.
The old record for manatee deaths, set in 2010, resulted from a lengthy cold snap that killed hundreds of manatees, pushing that year's number of deaths to 766. That cold snap mostly affected younger manatees that had not yet attained breeding age, DeWit said.
This year's record die-off was driven by two causes -- one of which remains a mystery.
First, a massive bloom of red-tide algae along the state's southwestern coast caused 276 deaths early in the year. Red tide has been around for centuries and has killed manatees before. But this year was the worst red tide die-off ever recorded.
Meanwhile, a mysterious ailment has been killing manatees in the Indian River Lagoon on the state's east coast. That's been going on since last year but hit a fever pitch in the spring. Twenty-five died in March.
All told, 117 manatees have died in the Indian River Lagoon since July 2012, including one that died this month, according to Kevin Baxter, spokesman for the state marine science laboratory. No one can explain the die-off, which appears to be unprecedented.
Scientists are also baffled as to why scores of dolphins and pelicans died in the lagoon, too, or whether there is any connection among the unusual events.
The deaths of the three species may be a result of pollution-fueled algae blooms that wiped out some 47,000 acres of seagrass in the 156-mile-long lagoon that stretches along the state's Atlantic Coast.
Manatees normally eat seagrass, but with the seagrass gone, they turned to less healthful sources of nutrition. They ate a reddish seaweed called gracilaria. Tests have found "a suite of toxins" on the gracilaria, but there is no confirmation that that's what killed the manatees. And that would not normally affect dolphins and pelicans, which eat fish, not seagrass.
There was one piece of good news in the figures. This year, 71 manatees have been killed by boats. That's down from the 81 that were killed by boats in 2012 and well below the record of 95 in 2002.