The Broken Shell Problem

Oyster shells seem like straightforward storytellers. They pile up in middens, layer by layer, preserving traces of harvest, feast, and shoreline life stretching back thousands of years. For archaeologists, shell size has long been treated as a clue to past abundance. Bigger oysters implied less pressure; shrinking shells signaled overharvesting.

As global oyster populations decline and fisheries collapse, archaeologists may be able to inform effective management with perspectives of human-oyster connections stretching back millennia. Credit: Florida Museum / Kristen Grace

But what if that tidy equation bends under the weight of time, tides, and a pickaxe?

A new study in the Journal of Archaeological Science¹ argues that the archaeological baseline for oyster populations may be warped by a deceptively simple oversight: broken shells. The fragments often ignored during excavation might hold the key to understanding ancient fishing pressure more accurately. And they might reveal that some long-trusted reconstructions of coastal ecosystems need a second look.

In South Florida, two midden sites tell a sweeping story of feasting, ritual, and shoreline engineering. Yet their oysters whisper something quieter: a warning about survivorship bias.

Oyster shells found in archaeological middens are difficult to measure accurately because of their irregular shapes and tendency to break apart. Credit: Florida Museum / Kristen Grace