Recent research suggests that manatees might not be native to Florida, potentially having settled there only after European colonization.
Previously thought to have been long-time residents, archaeological findings now indicate that manatees were rare in pre-colonial times. This new understanding comes amidst concerns over climate change impacts on manatee populations, which, despite increasing since the mid-20th century, remain threatened by environmental changes.
Manatees: Florida’s Recent Residents?
New research indicates that while manatees are a beloved symbol of Florida’s marine environment, they may actually be relatively recent arrivals to the region.
This conclusion comes from a study co-authored by Thomas Pluckhahn, an anthropologist at the University of South Florida, and David Thulman, an archaeology professor at George Washington University. Their findings were published in the scientific journal PLOS ONE on November 20.
Historical Shifts in Manatee Populations
The paper, “Historical Ecology Reveals the ‘Surprising’ Direction and Extent of Shifting Baselines for the Florida Manatee,” suggests that for centuries, manatees occasionally ventured into Florida’s waters but primarily as transient visitors from their Caribbean habitats, such as Cuba, rather than permanent residents.
According to the researchers, manatees likely did not establish a lasting presence in Florida until after the arrival of European settlers.
Manatees and Climate: An Irony of Survival
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.
Archaeological Insights on Manatee History
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.
Tracing Manatee Bones: A Rarity in Finds
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.
Manatee Sightings: A Historical Perspective
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.
Climate Influence on Manatee Migration
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.
Manatee Population Growth and Future Challenges
Newspaper accounts from the late 1800s and early 1900s describe manatee sightings in warm water refuges like yacht basins and canal harbors, and later in areas near power plants.
The state’s current manatee population is between 8,350 and 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 seagrass 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.”
For more on this research, see How Florida’s Manatees Are Thriving More Than Ever.
Reference: “Historical ecology reveals the “surprising” direction and extent of shifting baselines for the Florida manatee (Trichechus manatus latirostis)” by Thomas J. Pluckhahn and David K. Thulman, 20 November 2024, PLOS ONE.
DOI: 10.1371/journal.pone.0313070
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1 Comment
“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.”
And their propensity for gathering at warm springs in the Winter suggests that the temperatures are still not optimal for them. What we see in Florida are pioneers trying to expand their range from the Caribbean.