Stable isotope reconstructions of shellfish harvesting seasonality in an estuarine environment: implications for Late Holocene San Francisco Bay settlement patterns

Seasonality estimates based on stable isotope analyses of shellfish remains has been an important thrust of settlement pattern reconstruction, allowing researchers to place people on the landscape at points in space at different times of the year. In exposed coastal settings seasonality reconstructions are typically dependent on annual changes in water temperature. This paper has two goals. First, we continue development of a method for determining shellfish harvest seasonality in estuarine environments where annual salinity changes, not temperature, drive isotopic variation. Second, we contribute to settlement pattern studies by showing how small and large sites can be linked into a single system by examining different site types and shellfish species. Our case study focuses on the Late Prehistoric period of the San Francisco Peninsula, includes a large shellmound (CA-SMA-6) and an ephemeral camp (CA-SFR-171), and examines clam (Macoma spp.) and mussel (Mytilus spp.) harvesting. In this case, data support a fission-fusion settlement pattern, with periods of dispersal during late winter through early summer and aggregation in late summer through early winter.