As of mid-May, 738 manatee deaths had been recorded this year, according to reports from the Florida Fish and Wildlife Conservation Commission. The total is nearly triple the five-year average for the same time period. Fewer manatees, 637, were reported dead all of last year.
About 300 of the manatee deaths have happened in Brevard County, the state says, where scientists believe years of sea grass losses led to manatees not having enough food where many of them winter near warm discharges from power plants.
State reports show 230 manatees turned up dead in Florida this February alone.
Week after week, de Wit said, veterinarians saw manatees with “severe emaciation,” as much as 40 percent underweight. Their muscles and fat had been wasting away, with damage also in their livers and hearts.
Through May 14, according to agency reports, 89 manatees had been rescued around the state. On the East Coast, de Wit said, blood data from manatees suggested some were suffering end-stage starvation. Even at aquariums and rehabilitation facilities, she said, the animals’ health improved slowly.
“If you can just sit still in a tank and get fed all the lettuce you need and you still take months . . . I think that’s telling,” she said.
The federal government has labeled the die-off an “unusual mortality event,” freeing up resources to help the state in the response.
Manatees are considered a threatened species; their status was upgraded from endangered a few years ago. On its website, the Fish and Wildlife Conservation Commission says a population estimate indicates there are at least 7,520 alive today.
The die-off, de Wit said, began in December. But researchers did not immediately clock the trend because they expected an uptick in deaths due to a sudden temperature drop at that time that would have stressed manatees anyway.
The situation got more dire during the first few months of 2021. The loss of tens of thousands of acres of sea grass in the Indian River Lagoon is the likely culprit, de Wit said. The area has been plagued by algal blooms, which are fed in part by nutrients in runoff and wastewater coming off land.
The sea grass problem will be hard to fix, especially because water quality is not ideal in the affected parts of the lagoon, said Ron Mezich, imperiled species management section leader at the Fish and Wildlife Conservation Commission. Algal blooms reduce water clarity, and sea grass relies on sunlight reaching it to grow.
Scientists and conservationists worry what could happen next winter, when manatees return to stay in the lagoon in major numbers.
The effects of the die-off may endure for years, de Wit said, with cascading issues in reproduction and manatees’ metabolism that would affect future generations.
Even though animals are spread out and eating now, she said, “it will take a long time for them to recover from what they went through this year.”
— Tampa Bay Times