The function of Late Archaic period (5000-3000 B.P.) shell rings has been a focus of debate among archaeologists for decades. These rings have been variously interpreted as a product of seasonal feasting/ceremonial gatherings, quotidian food refuse generated by permanent dwellers, or a combination of seasonal and perennial activities. Seasonality of shell rings can be assessed by reconstructing the harvest time of oysters (Crassostrea virginica), the primary faunal component of shell rings. We estimated the timing of oyster harvest at St. Catherines Shell Ring (Georgia, USA) by statistical modeling of size frequency distributions of the impressed odostome (Boonea impressa), a parasitic snail inadvertently gathered by Archaic peoples with its oyster host. The odostome samples from three archaeological excavation units were evaluated against resampling models based on monthly demographic data obtained for present-day populations of Boonea impressa. For all samples, the harvest was unlikely to start earlier than late fall and end later than late spring, indicating that shell deposits at St. Catherines Shell Ring formed seasonally with substantial harvesting activities restricted to non-summer months. For all samples, the resampling models indicated that harvesting activities likely occurred during multiple months. However, these analytical outcomes would also be expected in the case of extensively time-averaged records of short-term, non-summer harvest events. Regardless of the exact harvest duration, the results point to seasonal harvesting and suggest that Archaic populations may have opted out of consuming summer oysters to focus on other resources, avoid unpalatable food, decrease pathogen risks, or ensure sustainable harvesting.