More than 10 percent of Florida’s estimated manatee population has died since the start of the year, already surpassing the total number of manatee deaths in 2020, according to state wildlife officials.
A recent report from the Florida Fish and Wildlife Conservation Commission found there were at least 761 manatee deaths from Jan. 1 to May 28, compared with 637 all last year. At this rate, the 2021 total is well on its way to surpassing the highest year-end total in at least the last five years, when the commission recorded 824 deaths in 2018.
Experts believe that one reason for the deaths is that the Indian River Lagoon, a 156-mile estuary along Florida’s Atlantic coast in whose warm waters manatees forage every year, has lost tens of thousands of acres of sea grass. Water quality has worsened for years because of runoff from fertilizers, sewage and septic leaks, increasing algae blooms that kill the sea grass, said Jaclyn Lopez, Florida director for the Center for Biological Diversity.
“All those sources contribute to the influx of nitrogen and phosphorus in the area and serves as a steroid for algae,” she said, adding that sea grass die-offs have been documented for years.
The sea grass’s footprint in the lagoon has decreased by 58 percent since 2009, according to Charles Jacoby of the St. Johns River Water Management District.
“The lagoon is like a desert,” said Martine de Wit, a veterinarian with the Florida Fish and Wildlife Conservation Commission. “This past winter, it was hardly growing anything” and the manatees did not have an alternative to sea grass.
Ms. Lopez said that a big bloom of algae “tends to soak up all the oxygen in the water and it shades out the sunlight” from the sea grass.
When the water gets cloudy, she said, the sea grass dies.
“If there is no sea grass for the manatees, there is also no sea grass for other species,” she said. “The fact that manatees are dying from starvation signals there is something very wrong with the water quality.”
But there are other threats leading to the manatee deaths, including exposure to cold temperatures and collisions with boats. Forty-nine of this year’s deaths were attributed to watercraft collisions.
An unofficial mascot of Florida sometimes called a sea cow, the rotund manatee is a large, slow-moving aquatic mammal. There are about 6,300 manatees in Florida, according to the U.S. Fish and Wildlife Service. During colder weather, they tend to congregate near South Florida power plants, where they lounge in the warm water discharge.
They are federally protected under the Endangered Species Act and the Marine Mammal Protection Act. Manatees are also protected by the Florida Manatee Sanctuary Act of 1978, which states that “it is unlawful for any person, at any time, intentionally or negligently, to annoy, molest, harass or disturb any manatee.”
Patrick Rose, an aquatic biologist and the executive director of the nonprofit Save the Manatee Club, described manatees as a “sentinel species telling us that the ecosystem is in a catastrophic state of decline.”
He said manatees are like “gardeners of the aquatic ecosystem,” helping the sea grass become more productive.
They will lightly graze on the sea grass and move on, stimulating more growth, he said, thus enabling other species, such as rays and sea turtles, to feed on the grass.
To help protect the lagoon and other state waterways, the St. Johns River water district urges the public to use fertilizers wisely — only when lawns show need, and never just before rain — and to connect to a central sewer system where possible.
Catrin Einhorn contributed reporting.