Why manatees are likely not Florida natives

• November 20, 2024
• Research and Innovation

By Paul Guzzo, University Communications and Marketing

With a county named after them, license plates with their depictions and parks promoted as the best places to view the gentle herbivores, known as sea cows, manatees are undoubtedly a part of Florida culture.

But they might also be relatively new residents in the Sunshine State.

The evidence backing this theory is compiled in a research paper written by Thomas Pluckhahn, a professor of anthropology at the University of South Florida, and David Thulman, an archaeology professor at George Washington University.

According to their paper published in PLOS ONE, 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, such as Cuba.

It is possible that they did not become Florida fixtures until after Europeans colonized the future state in the 1500s.

In Tampa Bay, the manatee population wasn't deemed plentiful until the 1950s - right around the time USF was established in 1956.

"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 about 70 archaeological reports that included the systematic collection and analysis of animal bones.

"Those reports totaled nearly two million animal bones," Pluckhahn said. "Essentially, none 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 Pluckhahn said 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.

"But if that is true, we would surely expect Spanish and French explorers and colonial settlers to have mentioned at least seeing manatee," Pluckhahn said.

His review did not find such mentions in written accounts of expeditions led by Hernando de Soto, who landed in Tampa Bay in 1539, nor in the account of Fray Andrés de San Miguel, who lived among the Indians in northeastern Florida in 1595.

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.

Through the early 1900s, Florida newspaper reports treated seeing a manatee more as a spectacle than a norm. Then, beginning in the 1920s and 1930s, the print media began writing of routine sightings in Miami and St. Augustine, especially in places such as yacht basins and canal harbors, which are shallow warm water refuges. As time went on, more and more people began noticing manatees swimming in warm areas near power plants.

The paper says that 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.

So, what changed?

This might sound strange to those accustomed to the state's humid days and sunburn, but Florida waters were once too frigid for manatees due to what is known as the Little Ace Age, which was a period of intermittent cooling beginning in the 1200s and lasting through the 1800s.

"There are descriptions from St. Augustine and elsewhere that winters were colder in the 1500s and 1600s," Pluckhahn said. "When the effects of the Little Ice Age started to fade, that was maybe the initial impetus for manatees extending their range northward to Florida."

Then, warming waters caused by the advancements of humans helped convince the manatees to stay and breed.

The irony doesn't escape Pluckhahn.

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 still threatens Florida manatees.

"Pollution is killing a lot of the sea grass that the manatees eat," Pluckhahn said. "Plus, as we wean ourselves off fossil fuels and shut down power plants, we are taking away a refuge from them."