University of Georgia

Sophisticatedly engineered ‘watercourts’ stored live fish, fueling Florida’s Calusa kingdom

Photography By Dorothy Kozlowski, Zachary Randall
Calusa man rowing boat
The Calusa kingdom had an estimated 20,000 people and ranks among the most politically complex groups of hunter-gatherers of the historic world. Uniquely, it was powered by fishing, not farming, leaving a central question: How could the Calusa store enough food to sustain population growth and fuel large-scale construction projects? (Illustration courtesy of Florida Museum/Merald Clark)
Calusa harvesting fish with nets
Once fish were captured in watercourts, they were likely harvested with seine or dip nets or speared, said archaeologist William Marquardt. (Illustration courtesy of Florida Museum/Merald Clark)

new study led by University of Georgia researcher Victor Thompson points to massive structures known as watercourts as the answer. Built on a foundation of oyster shells, these roughly rectangular enclosures walled off portions of estuary and likely served as short-term holding pens for fish before they were eaten, smoked or dried. The largest of these structures is about 36,000 square feet—more than seven times bigger than an NBA basketball court—with a berm of shell and sediment about 3 feet high. Engineering the courts required an intimate understanding of daily and seasonal tides, hydrology and the biology of various species of fish, researchers said.

The watercourts help explain how the Calusa could rely primarily on the sea.

“What makes the Calusa different is that most other societies that achieve this level of complexity and power are principally farming cultures,” said William Marquardt, curator emeritus of South Florida Archaeology and Ethnography at the Florida Museum of Natural History. “For a long time, societies that relied on fishing, hunting and gathering were assumed to be less advanced. But our work over the past 35 years has shown the Calusa developed a politically complex society with sophisticated architecture, religion, a military, specialists, long-distance trade and social ranking—all without being farmers.”

map show location of Mound Key, FL and lidar map shows standout features of Mound Key
Left: Mound Key was likely the seat of Calusa power for 500 years. By the 16th century, the Calusa kingdom stretched from the Florida Keys to the southern edge of Tampa Bay. Right: A remote sensing map reveals some of Mound Key’s standout features, including two large shell mounds, the grand canal and two massive watercourts flanking the island’s southwest shoreline. (Images by Thompson et al. in PNAS)

The fact that the Calusa were fishers, not farmers, created tension between them and the Spaniards, who arrived in Florida during the 16th century when the Calusa kingdom was at its zenith, said Thompson, director of UGA’s Laboratory of Archaeology.

“The Spanish soldiers, priests and officers were used to dealing with agriculturalists, such as the people they colonized in the Caribbean who grew maize surpluses for them,” Thompson said. “This would not have been possible with the Calusa. In fact, in a late 1600s mission attempt by the Franciscans, hoes were unloaded off the ship, and when the Calusa saw this, they remarked, ‘Why didn’t they also bring slaves to till the ground?’”

Thompson, Marquardt and colleagues analyzed two watercourts along the southwest shore of Mound Key, an island in Estero Bay off Florida’s Gulf Coast and the seat of Calusa power for about 500 years.

These courts, still visible today, flank the grand canal, a marine highway nearly 2,000 feet long and averaging 100 feet wide, which bisects the key. Both have yards-long openings in the berms along the canal, possibly to allow Calusa to drive fish into the enclosures, which could then be closed with a gate or net.

The team studied the watercourts and surrounding areas using remote sensors, cores of sediment and shell, and excavations. The bisected key features two large shell mounds, one on either side of the island. Remote sensing showed slopes leading from the watercourts to the top of the mounds, which may have been causeways for transporting food. On the shoreline, researchers found evidence of burning and small post molds, possibly for racks used to smoke and dry fish.

woman and man look at artifact
UGA’s Victor Thompson is lead author on a new study that sheds light on how the coastal Calusa kingdom managed to keep fish from spoiling in the subtropics. Above, Thompson and Anna Semon, from the American Museum of Natural History, examine an artifact from a collection at the university’s Laboratory of Archaeology. (Photo by Dorothy Kozlowski)

Radiocarbon dating suggests the watercourts were built between A.D. 1300 and 1400—around the end of a second phase in the construction of a king’s manor, an impressive structure that would eventually hold 2,000 people, according to Spanish documents.

A.D. 1250 also corresponds to a drop in sea level, which “may have impacted fish populations enough to help inspire some engineering innovation,” said Karen Walker, Florida Museum collection manager of South Florida Archaeology and Ethnography.

Fish bones and scales found in the western watercourt show the Calusa were capturing mullet and likely pinfish and herring, all schooling species. Florida Gulf Coast University geologist Michael Savarese’s analysis of watercourt core samples revealed dark gray sediment that was rich in organic material, suggesting poor circulation. High tide would have refreshed the water to some extent, Marquardt said.

“We can’t know exactly how the courts worked, but our gut feeling is that storage would have been short-term—on the order of hours to a few days, not for months at a time,” he said.

While researchers previously hypothesized watercourts were designed to hold fish, this is the first attempt to study the structures systematically, including when they were built and how that timing correlates with other Calusa construction projects, Marquardt said.

The Calusa dramatically shaped their natural environment, but the reverse was also true, Thompson said.

Calusa manor capable of holding 2,000 people
Atop a 30-foot-high shell mound, the Calusa constructed an expansive manor capable of holding 2,000 people, according to Spanish records. Fish stored in Mound Key’s watercourts may have provided the food resources needed to complete the project. (Illustration courtesy of Florida Museum/Merald Clark)

“The fact that the Calusa obtained much of their food from the estuaries structured almost every aspect of their lives,” he said. “Even today, people who live along coasts are a little different, and their lives continue to be influenced by the water—be it in the food they eat or the storms that roll in on summer afternoons in Southwest Florida.”

The study was published this month in the Proceedings of the National Academy of Sciences.

Funding for the research was provided by the National Geographic Society, the John S. and James L. Knight Endowment for South Florida Archaeology and the National Science Foundation.

Fish bone and scales, such as this fragment of a mullet scale, revealed which species Calusa were capturing. (Photo courtesy of Florida Museum/Zachary Randall)