Pismo Clam (Tivela stultorum) Harvesting on Middle Holocene Santa Rosa Island, California
Pismo clams (tivela stultorum) are relatively common in California’s surf-swept, sandy beaches, and archaeological specimens have been used as proxies for sand beach accretion and El Niño (ENSO) periodicity during the last 10,000 years. Native Americans in coastal southern California harvested Pismo clams throughout the Holocene, but these clams are generally rare in Channel Island archaeological sites. Here we report on human harvesting of Pismo clams at CA-SRI-209, located near Southeast Anchorage on Santa Rosa Island. Excavation of three discrete shell midden deposits produced evidence for intensive harvesting of California mussels (Mytilus californianus) between 5,030 and 4,820 cal B.P., and Pismo clams from about 4,770 to 4,310 cal B.P. Ancient Pismo clam sizes and population data from eastern Santa Rosa Island suggest that people harvested Pismo clams infrequently during the Holocene, with the CA-SRI-209 sample representing a population of similar sized (~83 mm. in height) individuals that fall within the size range of modern Pismo clams measured from the same area today. The timing of intensive Pismo clam harvests on Santa Rosa and adjacent Santa Cruz Island differs from that of the western Santa Barbara coast and hypo- thesized decreases in Middle and Late Holocene ENSO frequencies. Pismo clams are common prey of sea otters (Enhydra lutris), and it is possible that the abundance of Pismo clams in island archaeological assemblages may re ect a dearth of otters in local catchments.