Even as temperatures have warmed this spring and some Florida manatees have left the Indian River Lagoon, where many of them died this winter without enough food to eat, researchers are finding survivors up and down the coast struggling with prolonged effects of starvation.
“This event is not over yet. We are still picking up occasional cases with the effects of starvation,” said Martine de Wit, a veterinarian in the state’s marine mammal pathology lab. Cases have been documented as far as Georgia, she said. “These animals started to eat, but their bodies could not resolve those effects of prolonged starvation.”
As of late last week, 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 5-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 seagrass losses led to manatees not having enough food in the place 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. She spoke Wednesday at a regular forum on the status of manatee research and conservation in Florida.
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 respond.
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 seagrass 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 from land.
“We’ve been talking about this for a long time,” de Wit said. For a while, she said, it seemed as though manatees were managing to sustain themselves by going to other feeding zones or eating other vegetation.
The seagrass 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 seagrass relies on sunlight reaching it in order 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, according to de Wit, with cascading issues in reproduction and manatees’ metabolisms that would affect future generations.
“Even animals that are spread out and are eating now,” she said, “it will take a longtime for them to recover from what they went through this year.”