Stable Isotopes from Marine Shells, Ancient Environments, and Human Subsistence on Middle Holocene Santa Rosa Island, California, USA

Abstract

We report the analysis of stable isotopes on a suite of marine and estuarine shellfish, along with faunal data, from a Middle Holocene red abalone midden on Santa Rosa Island, California. Our research suggests that people harvested red abalones, mussels, and estuarine shellfish at about 6000 cal BP. Later in time around 4300 cal BP, people relied on California mussel and sea urchin with only trace amounts of red abalone and no estuarine taxa. Analyses of stable oxygen isotopes from California mussel, red and black abalone, and Venus clam shells indicate that a significant change in sea surface temperatures (SST; ∼2 • C) between the two occupations is the primary cause for this discrepancy. Differences between the isotopic values of California mussel and black and red abalone shells from the same strata also suggest that people were probably diving in fairly shallow waters for red abalone rather than obtaining them from the intertidal zone. Our research and other studies 233 Torben C. Rick et al.in the region suggest that environmental and cultural variables (e.g., human harvest pressure) may have worked together to cause changes in the composition of local shellfish habitats. These data demonstrate the importance of conducting stable isotope analysis on a variety of different shellfish species (e.g., rocky coast, estuarine, and other taxa) in concert with traditional midden analysis to help understand ancient environmental, biological, and cultural developments in coastal, island, and other aquatic settings.

Human impacts on ancient shellfish: a 10,000 year record from San Miguel Island, California

“…Few studies from California's Channel Islands have measured changes in shellfish sizes through time (with measurements of mussels and abalones from three sites on Santa Cruz, two on Santa Rosa, three on San Clemente, and two on Santa Catalina), but these generally confirm our results (see Braje et al, 2007b;Douros, 1993;Raab, 1992;Rick et al, 2006;Rosenthal, 1988;Sharp, 2000). Studies of California mussel shells from trans-Holocene sequences on Santa Rosa and Santa Cruz provide evidence of a decline in shell size through time, with the biggest decrease in the Late Holocene (Braje et al, 2007b;Sharp, 2000).…”

Red abalone collecting and marine water temperature during the Middle Holocene occupation of Santa Cruz Island, California

“…This value compensates for the over-representation of portions of the annual cycle, or cycles, when the shell grows more slowly (see Jones and Kennett, 1999). In contrast, the average of the values obtained from a shell, which has been used in previous studies (Glassow et al,1994;Rick et al, 2006) may be skewed toward one end of the temperature range if the number of values per shell is small. The five shells from the South Unit strata yielded an average midpoint temperature of 14.7 C (s.d.…”

“…He argued that SSTs were not necessarily cooler compared with today, that diving for red abalone was a distinctive cultural practice that was abandoned w5300 cal BP, and that cessation of diving for red abalone was the result of an expansion of people onto the Channel Islands who did not practice diving for shellfish. Rick et al (2006) also proposed that diving for abalone was practiced by island occupants of the 6300e5300 cal BP period. Their argument was based on an oxygen isotopic offset between California mussel and red abalone shells within the same midden deposit on Santa Rosa Island, suggestive of intertidal collection of mussel and subtidal collection of red abalone.…”

Intensification of shellfish exploitation: evidence of species-specific deviation from traditional expectations

“…Significant amounts of archaeological research on prehistoric shellfish exploitation indicate that increased human predation pressure on mollusks produces unique archaeological signatures Jerardino, 2008;Glassow, 1996;Rick et al, 2006). Affirming Broughton's proposed indices for resource depression as a product of intensification in exploitation, a frequent observation in shellfish analysis is the occurrence of a reduction in size or age of marine mollusks accompanied by change in species representation through a shell midden sequence.…”

“…Although Broughton's analyses rely on faunal data from the San Francisco Bay and the Sacramento Valley of California, case studies from around the world affirm this archaeological pattern as evidence of resource depletion in vertebrate and invertebrate species alike. Indeed, a significant amount of research in recent years has documented evidence of economic intensification and resource depletion of invertebrate shellfish populations by prehistoric coastal hunter-gatherers around the world (e.g., Andersen, 1981Andersen, , 2001Botkin, 1980;Braje, 2007;deBoer et al, 2000;Douros, 1993;Jerardino, 1997;Klein et al, 2004;Koike, 1986;Mannino and Thomas, 2002;Mellars, 1978;Milner et al, 2007;Morrison and Hunt, 2007;Nagaoka, 2002;Swadling, 1976;Raab, 1992;Rick and Erlandson, 2008;Rowley-Conway, 1984;Rick et al, 2006;Rick et al, 2006).…”