Reconciling oxygen isotope sclerochronology with interpretations of millennia of seasonal shellfish collection on the Pacific Northwest Coast

The results of high-resolution stable oxygen isotope (δ18O) sclerochronology of 139 butter clam (Saxidomus gigantea) shells from nine archaeological shell midden sites on the central coast of British Columbia, Canada demonstrate clear patterns of multi-season harvest at most sites and specific seasonal harvest at particular site locations. Although the results are based on small numbers of shells relative to an unknown number of seasonal clam harvesting events over the centuries or millennia of site occupation, they can be interpreted with confidence based on regional inter-site consistency, fit with a broader range of ancillary archaeological evidence, and the relative stability of seasonal patterns through iterative increases in sample size. On the basis of these results we outline a pragmatic approach to the selection of shells for seasonality analysis and for the interpretation of seasonal harvest patterns. This approach depends neither on the indeterminate reliability of probabilistic sampling of midden deposits and constituents or the prohibitively costly and still potentially unreliable use of large shell samples drawn from deposits distributed across sites.