Who needs a fridge when you have water courts?

Fish were captured and stored by Native Americans of southwestern Florida in complex walled structures called watercourts, constructed of shell and other sediments. These structures were engineered with knowledge of tidal systems, hydrology, and the biology of species to be stored in these courts.

This is an excerpt from a fascinating archaeological study by Victor Thompson (University of Georgia) and colleagues, published recently in PNAS.

Here’s the lowdown.

In Florida’s southwest coast there lived a Native American people known as the Calusa—most notable for having developed a complex culture based on estuarine fisheries rather than agriculture. This new study provides compelling evidence for the function of their sophisticated engineering structures. Lacking refrigeration technology in a tropical climate—and being dependent on perishable fish—they needed an innovative food storage solution. So around 1300 AD they developed water courts—large-scale fish traps that regulate the tidy to provide a store for live fish. Two large water courts (perhaps 50m by 50m) were constructed at either side of a sea estuary and connected to a canal network, likely used to transport the fish catch landward.

How important was this feat of hydrological engineering?

We argue that continued population growth and the increasingly centralized power of ruling lineages at Mound Key were likely underwritten by the surplus production of fish, akin to such trajectories observed among stratified agricultural societies.

…and…

The growth of the Calusa polity and the power and influence of Mound Key would have been a highly complex system that required a large degree of confidence (i.e., food security and surpluses) among participating groups to build such a system. In sum, we view the construction of the watercourts as part of the economic base of Mound Key’s prominence as the capital.

Reading this paper, I was struck by the breadth of evidence the archaeologists used to construct their theory. The investigation included: remote sensing, coring, excavations, radiocarbon dating, vertebrate faunal analysis, and hydrological experiments—all conducted rigorously. The evidence from each investigation is then brought together beautifully, leaving one with the impression that the archaeologists set the bar way higher than hydrologists do when it comes to preparing a manuscript and demonstrating a theory.

In case you’re interested, the hydrological analysis employs Darcy’s Law to model the loss of water during low tides, accounting for alternative possible hydraulic conductivities. The analysis demonstrates the capability of the water court structures to regulate the tidal cycle and function as live fish stores.