Shellfish, seasonality, and sedentism : δ18O analysis of California mussels from early Holocene shell middens on San Miguel Island, California

We estimate seasonality of shellfish harvest and site occupation for four Early Holocene shell middens on California's San Miguel Island using a dataset of 449 δ18O measurements from 84 mussel shells (Mytilus californianus). Seasonality was assigned to prehistoric mussels using paleo sea-surface temperature (PSST) estimates from isotopic data obtained across full shell profiles. The results suggest that PSSTs around San Miguel Island were generally cooler between ∼10,000-8600 calBP and that mussels were harvested in a range of water temperatures which suggest a mix of seasonal and year round harvesting at the four sites. Two substantial shell middens dated to ∼10,000 and ∼9000 calBP appear to have been residential basecamps where Paleocoastal peoples harvested shellfish during all four seasons. These data suggest that Early Holocene peoples occupied the Channel Islands year round and highlight the importance of stable isotope analysis of marine shells for helping evaluate human settlement and subsistence strategies along the Pacific Coast. (author)