ORLANDO, Fla., April 2 (UPI) -- Florida's Native American Calusa nation had much more advanced engineering systems than previously realized, and they allowed members to capture and store fish in large enclosures, according to a new study.
The research provides a greater understanding of how the Calusa fishing techniques, rather than farming skills, propelled the tribe to political influence over the southern portion of the Florida peninsula for hundreds of years.
It also gave researchers a clearer picture of how the Calusa capital at Mound Key -- 20 miles south of Fort Myers -- was built and when it became the focal point of a large kingdom about 1300.
The use of the enclosures, called watercourts by the study's authors, began as the Calusa influence expanded, according to the study.
Designing and building the enclosures required an intimate understanding of daily and seasonal tides, hydrology and the biology of various species of fish, the researchers said.
Fish driven in
The watercourts were built on a foundation of oyster shells, walling off portions of an estuary. Fish were driven into the enclosure through a gap, which was then blocked with a net or lattice.
The largest of the structures, which the study says still is visible, is about 36,000 square feet -- seven times bigger than a professional basketball court -- with a berm of shell and sediment about 3 feet high.
"These structures were for large surplus capture and storage of aquatic resources that were controlled and managed by corporate groups," wrote the study's authors, who are researchers from the Florida Museum of Natural History and the University of Georgia.
The clearer picture of the Calusa food supply also allows greater insight into the structure of their society, said Victor Thompson, one of the authors and director of the University of Georgia's Laboratory of Archaeology.
"We've known for some time that the upper echelons, the king and his family, and also the warriors, didn't have to work for food," Thompson said.
Scientists spent five years probing and imaging the structures at Mound Key State Archaeological Park. The findings were published this week in the Proceedings of the National Academy of Sciences.
The Calusa lived mostly in southwest Florida, in what is now the Fort Myers area and to the south, but their influence extended to the entire southern peninsula, according to the study. For centuries, the Calusa wielded military power, trading and collecting tribute along routes that ran for hundreds of miles.
Unlike the Aztecs, Maya and Inca, who built their empires with the help of agriculture, the Calusa nation was founded largely on fishing. The Calusa were known to Spanish explorers and settlers, but their population declined rapidly because of disease and slave trade in the 1700s.
"The results of this study gave us more knowledge about the timing and history of the capital, because this was occurring at the same time as the king's house was rebuilt into a much larger structure," Thompson said. "It tells us how the capital wound up being structured as it was."
Historians have long suspected the enclosures were intended for fish, but the new study looked at how they might have worked, said Bill Marquardt, researcher and former director of the Florida Museum of Natural History.
"We think we know now what they are and when they were built," Marquardt said. "We know they stored fish because there are fish bones and scales found in the well-preserved sediment Right offshore from there, we find none of that."
The surplus fish also boosted the Calusa influence because their society could offer food to neighbors and trading partners, Marquardt said.