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Manatee populations have recovered significantly over the last few decades, after hunting and habitat loss decimated their populations. But in early 2021, manatee deaths have suddenly spiked, with nearly 360 known deaths as of mid-February, reports the Florida Fish and Wildlife Conservation Commission (FWC). A combination of factors, including problematic trends in polluted waters and depleted food, could be driving the die-off event of these charismatic mammals, dubbed "sea cows." But the certain cause or causes of this abrupt spike are still being investigated, as a majority (68 percent) of dead manatees have not yet been necropsied by the state.
"It's difficult to make a determination," explained Edie Widder, a marine biologist and senior scientist at the Ocean Research and Conservation Association in Florida, a conservation organization. "Without the data, I don't see how you can make any kind of judgment."
Over the last five years, an average of 117 manatees were recorded dead over the same January-February time frame, meaning three times as many manatees have died so far in 2021. There have been too many sick or dying manatees to save in the estuaries off the Atlantic coast of Florida.
"It was so significant here that we couldn't intervene in many cases," explained Patrick Rose, the executive director and aquatic biologist for Save the Manatee Club, a manatee conservation organization. A partnership of conservation groups, including Save the Manatee Club, has already rescued over 50 struggling manatees this year and returned dozens back to the water, Rose said.
The Florida Fish and Wildlife Conservation Commission said it's probing the spike in deaths. "The FWC is investigating a high level of manatee mortalities and responding to manatee rescues on the central and south Atlantic coast of Florida," the agency said in an email. "The investigation is in progress, and we will be sharing information as it becomes available," the agency added.
Some of the dead manatees died from cold stress, the Florida Fish and Wildlife Conservation Commission reported. This is often normal. Manatees are warm-adapted animals that can struggle during winter.
But many manatees could be starving. "We’re seeing a significant number of manatees dying from starvation and malnutrition," Rose said. This suggests manatees might be victims of environmental decline and pollution, which ultimately kills off the food, seagrass, they devour. "Lack of forage is a big driver," said Rose, noting the depletion of seagrass in some important manatee habitats.
The loss of seagrass is a continued consequence of overloading the coastal areas where manatees feed with nutrient pollution — largely from fertilizer runoff, sewage disposal, and wastewater treatment plants. This deluge of nutrients allows algae to blossom and darken the water, depriving seagrass of sunlight. Seagrass dies, and manatees can starve. Seagrass coverage has declined significantly since 2011.
A manitee rescue. Credit: Save the Manatee Club In the long run, polluting Florida estuaries, like the sprawling and biologically diverse Indian River Lagoon, clearly hurts manatee populations.
"It's heartbreaking because they’re dying from the unintended consequence of another problem," said Quinton White, the executive director of the Marine Science Research Institute at Jacksonville University. "I've never met anyone who wanted to hurt a manatee. But that's what's happening right now. We’re paying the price for that [pollution] now."
These polluted environments are harmful to wild Florida animals and marine life, regardless of the pollutant's current impact on manatees. In late 2020, thousands of fish, rays, and other creatures washed up dead on Indian River Lagoon shores. But the deaths of the large, popular manatees provide an especially vivid example of how polluted or disrupted ecosystems can impact wildlife.
"These are the kinds of red flags that are popping up on our life support systems across the planet," said Widder.
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Yet fully understanding this specific spike in deaths requires comprehensive necropsies, emphasized Widder. Manatees, for example, are susceptible to pesticides. The Florida Fish and Wildlife Conservation Commission didn't comment on necropsies to Mashable, but told The Daytona Beach News-Journalthat the workload from identifying the dead manatees combined with Covid-19 safety protocols has slowed their progress.
Cleaning up manatee habitat, like the Indian River Lagoon, is not easy, but it's possible. "It's a solvable problem," said White. Polluting muck from the lagoon floor is being cleaned up, and some fertilizer bans have gone into effect. But to stop the algae blooms that kill off seagrass, these efforts are still likely not nearly enough. Pollutants from biosolids, wherein sludgy sewage is used as fertilizer on ranches, flows into Florida lakes and rivers. The consequences stream downriver.
"The grass is being destroyed," said White, referencing the food manatees eat.
Manatees, adapted to thrive in warm environments, can't simply just find other places to live. They're largely reliant on society keeping their habitats unpolluted.
"It's up to us to be their voice," said Rose.