An investigation of hunter-gatherer shellfish foraging practices: Archaeological and geochemical evidence from Bodega Bay, California

The Pacific coast of western North America has been visited and exploited by hunter-gatherers for the last 10,000 years or more. Initial occupation culminated with the well-known historic pattern in which groups remained year round on the coast subsisting on shellfish, fish and marine mammals. Whereas abundant archaeological data exist from other coastal regions of western North America, our understanding of the conditions that led to a more maritime focus in northern California is limited. To address this issue, shellfish subsistence behavior is investigated using a tripartite approach focused on invertebrate assemblages excavated from discrete (14C-dated) archaeological components near Bodega Bay, California. The first two approaches examine changes in species and habitat selection over the last 9000 years using the prey choice and patch choice models of foraging theory. The third approach uses the shell delta18O and delta13C of Mytilus californianus (California sea mussel) specimens from the same components to determine changes in shellfish harvest seasons (annual harvest intensity).; Experimental shellfish return rates are used to develop prey and patch types and ranks, and hypotheses incorporating paleoenvironmental variability. A modern calibration study verifying that delta18O and delta 13C can be used to determine season of sea mussel death in this region is presented. Expectations are tested with shellfish remains recovered from Bodega Bay archaeological sites. Analyses examine temporal trends in prey selection, patch (tidal zone and substrate) choice, seasonality of harvest, mobility and settlement. Results indicate that diet breadth did not change over the last 9000 years although it did narrow in late Holocene processing camp assemblages when sea mussel remains dominated both camp and residential base assemblages. The stable isotope results demonstrate that the season of shellfish harvest also changed, occurring predominantly in the fall/winter during the early and middle Holocene, and in the fall/winter and spring/summer during the late Holocene. Results suggest year round harvest and occupation during the late Holocene and occupation with the seasonal employment of task groups from local residential bases. Findings are compared with regional data to explore the spatial extent of the observed patterns and the applicability of the model to other coastal regions.