Florida’s recent winter gave a blow to its West Indies manatees, iconic marine mammals that are a major tourist attraction. In the first 5 months of this year, 761 manatees that overwintered in a Florida lagoon died, according to the state’s Fish and Wildlife Conservation Commission (FWC). The number represents approx. 10% of Florida’s population Trichechus manatus latirostris, the subspecies there, and is more than the total number of seats that died across the state in 2020.
Cause of death: hunger due to the loss of seagrass in increasingly polluted waters, a problem that is not easily solved. “I would not be surprised if this happens again next year,” said Daniel Slone, a research ecologist at the US Geological Survey (USGS).
The only vegetarian marine mammal, manatees – often called sea cows – thrive in subtropical waters, where they feed on seabed grass, algae and floating plants. In the Atlantic Ocean north of the equator, there are two subspecies. One lives in the southern part of the Caribbean. The other bends through Florida’s rivers, springs and coastal waters and sometimes deviates north to Massachusetts in the summer. Manatees can not withstand colder water than 20 ° C, so in Florida in colder months they are collected in hot springs or in the water discharged at coastal power plants from cooling generators.
A key point is the Indian River Lagoon in the middle of Florida’s east coast, which hosts about 2,000 lakes each winter thanks to water spills from power plants. Agricultural runoff, wastewater discharges and other man-made activities have increased. Since 2011, the excess nitrogen and phosphorus flowing into waterways has nourished long “superflowers” of brown or green algae that make the lagoon’s water “look like pea soup,” says Martine deWit, an FWC veterinarian. As sunlight is unable to penetrate the lagoon, seagrass and other photosynthesizing organisms disappear. “Every year the seagrass gets a little worse,” says deWit.
This year, “the hammer just fell,” Slone says. The winter of 2020–21 started with a cold snow, which required manatees to increase their calorie intake to stay warm. Thereafter, the animals remained, even though there was not enough grass to feed all the manatees. “They chose heat over being hungry,” says deWit. Some of the starving animals that came through the winter and began to spread across the coast of Florida are now found dead elsewhere because they could not recover.
About 10 years ago, USGS researchers determined that The Indian River Lagoon could sustain the number of manatees who learned from their mothers to go there. “That is clearly not the case now,” Slone said.
At present, the possibilities for restoring seagrass are limited. “We do not want to replant seagrass until we have done so [better] water quality, ”says Charles Jacoby, environmental researcher with St. Johns River Water Management District, based in Jacksonville, Florida. His agency is only five years inside a 15-year plan to lower the nutrient load in the lagoon. The plan includes the removal of “muck” – muddy, nutrient-rich sediments that have accumulated in the lagoon as well as in canals and tributaries because there is not enough water flow to flush it out. It also requires the improvement of sewage treatment plants and the connection of households that now use septic tanks for the sewer system. Because these solutions will take time, he and others are considering short-term corrections for the manatees, such as feeding the sea cows or trying to lure them to winter elsewhere.
But other overwintering spots are becoming rarer, says Jaclyn Lopez, a lawyer and manate expert with the Center for Biological Diversity, a conservation organization. “We have not done enough to preserve hot water habitats.”
Until now, Florida manatees, which were one of the first species to be placed on the list of endangered species in the United States in the 1970s, seemed to be doing better. In 1991, the first air count counted about 1,200 individuals. Now it is estimated to be 7000 to 8000. In 2017, this progress prompted then-President Donald Trump’s administration to upgrade the manate’s legal status to “Threatened” under the federal law on endangered species, despite objections from conservation groups.
Seabirds also fall under the protection of the federal law on the protection of marine mammals. On May 26, a working group set up under this action declared the proclamation as one “Unusual mortality,” which triggers a federally funded investigation into the cause.
Meanwhile, seabird rehabilitation centers have been overcrowded with emaciated animals, and officials are struggling to find new places to care for sick animals. “We do not have the ability to meet this rescue need,” Lopez said.
But Sloan and Jacoby are optimistic about the species’ future in Florida. The population on the state’s west coast is doing well. And the long-term prospects for manatees on Florida’s east coast, Jacoby says, “are probably okay.”