Manatees might be relatively recent arrivals to Florida, USF study finds

TAMPA, Fla. (Nov. 20, 2024) – New research suggests that while manatees are an indelible part of Florida’s seascape, they might also be relatively new residents in the Sunshine State.

The findings are detailed in a study co-authored by University of South Florida anthropologist Thomas Pluckhahn and David Thulman, an archaeology professor at George Washington University, and scheduled to publish in PLOS ONE on Nov. 20 at 2 p.m. The embargo will lift at that time.

The paper, “Historical Ecology Reveals the ‘Surprising’ Direction and Extent of Shifting Baselines for the Florida Manatee,” (link will be live when the embargo lifts) concludes that for centuries, manatees might have occasionally swum in Florida waters, but possibly more so as tourists than residents, staying for a short visit before returning to their Caribbean homes like Cuba.

It is possible that they did not become Florida fixtures until after Europeans colonized the future state, the research suggests.

In Tampa Bay, the manatee population wasn’t deemed plentiful until the 1950s. And, in a twist of irony, manatees’ Florida residency was fueled by the same factor that now threatens their existence – climate change.

“It is commonly assumed that Florida manatee populations were once larger than they are today,” Pluckhahn said. “Many will find the results surprising, not only because it contradicts this assumption but also because it indicates the complexity of changes that have taken place in the Anthropocene,” the current period during which human activity has most-influenced climate and the environment.

The motivation for the research was fueled by Pluckhahn’s realization that there was a lack of evidence pointing to a large population of manatees in Florida’s pre-colonial era.

“Based on my own experience and talking to other archaeologists, we agreed there was a rarity of manatee bones on archaeological sites,” said Pluckhahn, who has been a part of archaeological excavations in the Tampa Bay area since 2008. “It was particularly impressive to me because I’ve worked at Crystal River, which is an epicenter for manatees. We became more curious and decided to do a comprehensive review of archaeological and archival sources.”

That analysis involved reviewing around 70 archaeological reports that detailed the systematic collection and analysis of nearly two million animal bones. Essentially none of them were manatee.

An expanded review of other excavations did find a dozen reports of manatee bones that had been modified into tools or ornaments, but that is not enough to proclaim that the sea mammals had a large pre-colonial Florida population.

The paper hypothesizes that it is possible that manatees were not present at all in precolonial Florida and the tools and ornaments arrived here via Native Americans trading with those from the Caribbean.

“The problem with that is people have been looking for proof of contact between Florida and the Caribbean during the pre-colonial era for a long time and haven’t been able to nail it down,” Pluckhahn said.

Or, perhaps, manatees were in abundance but there is a lack of bones at excavation sites because the mammals were not hunted. However, manatees are not described in accounts of expeditions by explorers who landed in Tampa Bay in between 1528 and 1595.

The most logical hypothesis is that manatees were then later “present only in very low numbers in Florida as occasional visitors from the Caribbean and then settled here permanently,” Pluckhahn said.

The first reliable written narratives of manatees in Florida date to the period of British rule in the late 1700s, the paper says. But, even then, sightings were rare.

Beginning in the 1920s and 1930s, the print media began writing of routine sightings in Miami and St. Augustine, and by the mid-1950s “there were reports that manatees were ‘becoming more plentiful’ in Tampa Bay and a few were said to have become permanent residents’ of Crystal River,” the paper says.

What changed?

In short, Florida’s waters were once too frigid for manatees due to what is known as the Little Ace Age, a period of intermittent cooling beginning in the 1200s and lasting through the 1800s.

The authors suggest that as the effects of the Little Ice Age faded, manatees began extending their range northward to Florida. Warming waters caused by the advancements of humans subsequently helped convince the manatees to stay and breed.

Newspaper accounts from the late 1800s and early 1900s describe manatee sightings in warm water refuges like yacht basins and canals harbors, and later in areas near power plants.

The state’s current manatee population is between 8,350–11,730, according to the Florida Fish and Wildlife Conservation Commission. That’s enough that, in 2017, they were reclassified from endangered to threatened under the federal Endangered Species Act.

But manmade climate change is still a threat to Florida manatees, Pluckhahn said. “Pollution is killing a lot of the sea grass that the manatees eat. Plus, as we wean ourselves off fossil fuels and shut down power plants, we are taking away a refuge from them.”

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