Seasonality determinations from archaeological oyster shells: an experimental evaluation of incremental shell growth.

Abstract

This report describes a project where a procedure was established for systematically evaluating the usefulness of growth lines visible on the chondrophore of the left valve of oyster shells for determinations of season-of-harvest. The research had two primary objectives. The first objective was to compare several methods of analysis for accuracy and utility. The second major objective was to assess the applicability of the techniques to oysters grown in warm, southern waters. Methods that can be demonstrated to produce reliable seasonality determinations with the modern control samples can eventually be applied to archeological samples excavated from nearby late prehistoric sites, to establish whether similar growth patterns are interpretable on archaeological specimens. Those techniques that produce reliable results will have value as relatively simple, inexpensive methods of seasonality determination for archeological oyster shell. The goal was to provide archaeologists with a reliable tool for exploring the extent and variation of the seasonal contribution of oysters to the diet of people who lived along the Atlantic and Gulf coasts of North America. Because growth may vary between northern and southern waters, oysters were grown in two study locations: in the Patuxent River, a tributary of Chesapeake Bay in Maryland, where cold water temperatures were thought to cause winter growth breaks; and Dauphin Island Bay, on the Gulf coast of Alabama, where high water temperatures in summer were suspected of causing heat stress growth breaks. The project lasted for three and a half years and the results are described.