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.     

Inter-site variability in the season of shellfish collection on the central coast of British Columbia

High-resolution stable oxygen isotope analysis of the bivalve Saxidomus gigantea from shell midden sites was applied to identify seasonal patterns of resource procurement on the central coast of British Columbia, Canada. A total of 90 archaeological shells were examined from eight distinct sites spanning a 4500-year period. Combining micro-growth pattern analysis with high-resolution stable oxygen isotope sampling allows for a precise season of collection to be determined in estuarine bivalves recovered from archaeological sites. The results of the stable oxygen isotope analysis provide insights into seasonally structured harvest of S. gigantea (butter clam), which is associated with different types of sites. The results show a variety of patterns, including multi-seasonal collection, intensive seasonal harvesting and casual, supplemental use of butter clams at different locations.     

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

Oxygen isotope values derived from prehistoric mussel (Mytilus californianus) shell calcite are used to determine whether sea-surface temperatures in the vicinity of the Punta Arena site (CA-SCRI-109) on Santa Cruz Island, California, were cooler than present between 6300 and 5300 cal BP. This site and others in the western sector of the island dating to this period are distinctive because of the presence of large red abalone (Haliotis rufescens) shells, a species that historically has been subtidal around Santa Cruz and the other northern Channel Islands. Comparison of temperature values derived from archaeological shells with those from modern mussel shells, along with water temperatures derived from satellites, indicates that waters were cooler during the 6300 to 5300 cal BP period. These results are consistent with a previous study and support the interpretation that collection of red abalone during the 6300–5300 cal BP period was partly the result of cooler water temperatures that made this large mollusk more available to foragers in the intertidal or shallow subtidal zone.     

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

We use measurements of more than 11,000 marine shells from 41 archaeological components to construct a 10,000 year record of human impacts on ancient mussel and abalone stocks on San Miguel Island, California. General reductions in the mean size of mussel and abalone shells gathered through time are attributed to growing human population and predation pressure. Based on comparison with historically documented changes in shellfish communities caused by the local extinction of sea otters in the 19th century, changes in mean shell size and the abundance of other shellfish species may have been facilitated by Native American predation on sea otters as early as 7500 years ago. Despite having measurable impacts on local ecosystems, Native Americans on San Miguel harvested huge quantities of shellfish throughout the Holocene. Such long-term harvests appear to have been sustained by an early emphasis on fishing at lower trophic levels, by periodically shifting village locations, and by intensifying the use of finfish and sea mammals through time. This pattern of “fishing up the food web” contrasts with many modern fisheries, suggesting that the study of ancient fisheries can help us better manage our own endangered coastal ecosystems.     

Paleodietary analysis of a San Francisco Bay Area shellmound: stable carbon and nitrogen isotope analysis of late Holocene humans from the Ellis Landing site (CA-CCO-295)

The late Holocene archaeofaunal record of the San Francisco Bay Area demonstrates temporal declines in the abundance of low-cost, high-ranked marine and terrestrial resources. During later periods of occupation, faunal assemblages are often dominated by lower-ranked, higher-cost resources, suggesting an increase in diet breadth through time. Archaeological resource intensification models argue that this marks a late Holocene decline in foraging efficiency in the Bay Area, driven by human-induced harvest pressure. This study examines dietary change in the region using stable carbon and nitrogen isotope data from 65 human burials, spanning two temporal components (cal AD 55–890 and cal AD 762–1550) at the Ellis Landing site (CA-CCO-295). The strong linear relationship between collagen carbon and nitrogen isotope values reflects both marine and terrestrial food consumption, with individuals showing a high level of dietary variability at the site. No temporal trend or meaningful sex differences were found in isotope values. The widening of diet breadth predicted by the archaeofaunal record occurred prior to the occupation of the Ellis Landing shellmound site. The trend in exploiting a greater amount of terrestrial resources during the Middle and Late Period in central California was supported by isotopic evidence.     

Declines in Mammalian Foraging Efficiency during the Late Holocene, San Francisco Bay, California

Resource intensification models that have been posited for prehistoric California predict decreases in foraging efficiency during the late Holocene, Using implications of the fine-grained prey model of optimal foraging theory, I derive an index of the efficiency of vertebrate prey choice from the relative abundances of large- and small-sized prey items. I then test the intensification models with late Holocene mammalian faunas from San Francisco Bay shellmounds. Dramatic linear decreases in the relalive frequency of artiodactyls compared to the smaller sea otters (Enhydra lutris) throughout the occupational histories of particular localities strongly support the resource intensification models. The declines in artiodactyl abundances are not correlated with late Holocene climatic indices developed for this region, with changes in the seasonal use of shellmounds, or with technological innovations. An intra- and interregionally consistent pattern in declining abundances of large mammals in environmentally distinct regions throughout California suggests that resource depression driven by human predators may be the single most important cause of the declines. These patterns have far-reaching implications concerning the long-term human role in structuring prehistoric ecosystems.     

Prehistoric behavioral depression of cormorant (Phalacrocorax spp.) on the northern California coast

Resource depression is often assumed to result from the over-exploitation of a prey species leading to declines in its population, and therefore availability, to human hunters. However, two other forms of resource depression are noted in the ecological literature: behavioral and micro-habitat depression. Data presented in this paper demonstrate resource depression of cormorants (Phalacrocorax spp.), a coastally breeding and semi-pelagic bird genus, at a coastal site in northern California. Citing modern cormorant behavior and a lack of evidence for intensive rookery exploitation, it is argued that the observed resource depression resulted from changes in cormorant behavior that decreased encounter rates for human hunters. Such behavioral depression is cited as a buffer to the extirpation of prey in mainland settings.     

Boat-based foraging and discontinuous prehistoric red abalone exploitation along the California coast

Temporally and spatially discontinuous pulses of heavy prehistoric exploitation of red abalone (Haliotis rufescens) have been documented along the southern and central California coast. This article examines the very late (post-950 cal BP) appearance of numerous red abalone processing sites on the Monterey Peninsula in central California. We test three prominent explanations offered for the sudden onset of red abalone processing sites: trophic cascades resulting from human predation on sea otters, logistical foraging by inland residents, and changes in sea surface temperature. A trophic cascade appears to have occurred but does not fully explain the nature or timing of the phenomenon in the region.     

Mesolithic shellfish exploitation in SW Italy: seasonal evidence from the oxygen isotopic composition of Osilinus turbinatus shells

Oxygen isotope analyses were carried out on the topshell Osilinus turbinatus from archaeological sites with the aim to investigate the temporal exploitation patterns by Mesolithic groups inhabiting coastal caves in SW Italy. In order to assess the present day O. turbinatus intra-annual δ¹⁸O variability, living specimens were collected monthly at Marina di Camerota (SW Italian peninsula). Their shell-edges were analysed and the seasonal results were compared with archaeozoological material. Our findings show that Mesolithic O. turbinatus exploitation was carried out almost exclusively during the colder and intermediary seasons (e.g. autumn, winter, spring), with very sporadic harvesting during the warmer seasons. Results suggest a possible regional exploitation pattern of O. turbinatus by Mesolithic groups inhabiting this region.     

Diversity in North Pacific shellfish assemblages: the barnacles of Kit’n’Kaboodle Cave,Alaska

Although the dietary importance of barnacles is recognized in Europe and elsewhere around the world, indigenous use of barnacles on the Pacific coast of North America has not been well-documented. On the Northwest Coast, most shell middens located along estuaries are dominated by clams (such as Saxidomus, Protothaca, etc.), while those on the outer coast are dominated by mussels (Mytilus californianus). At Kit’n’Kaboodle Cave in southeast Alaska, the acorn barnacle Semibalanus cariosus is unusually abundant over a 3500-year period, but is replaced by mussels over time. These results are placed within a larger geographic context to more closely examine patterns of barnacle use by First Nations of the Pacific Northwest.     

Oxygen isotope seasonality in a temperate estuarine shell midden: a case study from CA-ALA-17 on the San Francisco Bay,California

Seasonality determination using stable oxygen isotope (δ¹⁸O) analyses in archaeological mollusk shell has been largely limited to aquatic settings where one of the two factors that control shell δ¹⁸O – water δ¹⁸O (or salinity) and temperature – is assumed to be constant. Open coastal marine environments reflect the former situation, and tropical estuaries constitute the latter. In an effort to expand stable isotope seasonality to an ecological setting where neither variable remains constant, we present a model of annual shell δ¹⁸O cycle of aragonite deposition derived from instrumental data on salinity and temperature from San Francisco Bay, California. The predicted range of modeled shell δ¹⁸O is consistent with observed δ¹⁸O values in prehistoric and modern shells when local conditions are considered. Measurements of δ¹⁸O taken at 0 mm and 2 mm from the terminal growth margin were made on 36 archaeological specimens of Macoma nasuta from a late Holocene hunter-gatherer site CA-ALA-17, and season of collection was inferred using the shell δ¹⁸O model. We conclude that shellfish exploitation occurred through the year with the exception of fall, which may indicate scheduling conflicts with acorn harvesting or other seasonally abundant resources elsewhere. The model supports the feasibility of stable isotope seasonality studies in temperate estuaries, provided that instrumental records are available to quantify the relevant water conditions at appropriate spatial and temporal scales.     

Insights into early Holocene hunter-gatherer mobility on the Peruvian Southern Coast from mollusk gathering seasonality

Quebrada de los Burros (QLB) is an early Archaic coastal archaeological site in southern Peru (∼18.1°S) and the most extensively studied in the area for this period. It was occupied from 10 to 6.5 ka by fishermen also practicing hunting and mollusk gathering. Shell growth lines in 116 individuals of the surf clam Mesodesma donacium were studied to determine the month of their death (±2 months). Our results show that, for the whole occupation period, mollusk gathering was a seasonal activity mainly practiced during austral spring and summer. A change occurred between the early and the middle Holocene: the mollusk gathering season in the middle Holocene occurred ∼3 months earlier in the year than in the older levels. This behavior change could have a cultural origin, rather than dictated by the environment for it is associated with changes in the lithic industry. QLB occupants also hunted herbivores in the nearby lomas ecosystems. These plant communities only grow during the fog season from June to December, suggesting that the site was occupied during this season. A comparison of the span of the mollusk gathering season and the lomas season suggests that, at least during the early Holocene, QLB was occupied all the year round. A permanent freshwater source and the proximity of the sea, the lomas, and raw lithic materials, provided ideal conditions for a permanent occupation. This result reveals a strategy based on a seasonal alternation between marine and terrestrial resources exploitation.     

Secular decline in cranioskeletal size over two millennia of interior central California prehistory: Relation to calcium deficit in the reconstructed diet and demographic stress

An osteometric study of residual rickets (RR) skeletal plasticity has been made of a time-ordered sequence of fifteen series of adult skeleton sets (n=359) from the Great Valley of central California (GV), spanning the three archaeological horizons of California Indian prehistory in this region: Early (EH), Middle (MH) and Late (LH). By least-squares linear regression analysis, a clear and continuous downward trend obtained in cranioskeletal size in both sexes, proceeding from EH to LH in the GV sequence, pari passu with a steady upward trend in the RR-15 score. To ascertain if dietary calcium deficit (CADEF), a known cause of active rickets, can explain the observed secular increase in RR, the aboriginal diet was reconstructed by the diet grid method: CADEF was found to rise from borderline in the EH, to moderate in the MH, to severe in the LH, as the subsistence base shifted gradually away from hunted prey, and storable seed foods—mainly leached acorn meal—became the dominant source of energy. Further regression analysis has shown that the secular upward trend in CADEF is highly correlated with the temporal clines of the GV sequence, directly with the RR-15 score, and inversely with cranioskeletal size: in round numbers, one grade of CADEF brings about a loss of 120 cm³ or 4 per cent in partial skeleton volume. Two biocultural influences—demographic stress (DS) in females, and the less common ‘male nutritional advantage interaction co-factor’ (MNAIC)—modulate the primary bone antitrophic CADEF effect: DS enhancing, MNAIC ameliorating.     

Hunting behavior and Neanderthal adaptability in the Late Pleistocene site of Pech-de-l'Azé I

The late Mousterian of Acheulian tradition (MTA) site of Pech-de-l'Azé 1 shows a very particular stratigraphic sequence characterized by numerous elements not usually found in Mousterian contexts such as avifauna exploitation and the use of hundreds of mineral pigments. Recent zooarchaeological and skeletochronological analyses provide new insights into the evolution of subsistence behaviors and settlement patterns of the Neanderthals that inhabited the shelter. Due to changes in hunting season, Neanderthals adapted their hunting strategies, exploiting various red deer populations which presented very different behavior. The evolution in the seasonal occupation of the shelter may have been the results of major modifications of its (series of roof collapsed) which induced a shrank in inhabitable space., which forced the Mousterians to adjust the way they used the cavity to its characteristics in order to optimize its exploitation. The conclusions underline the excellent adaptability of the Neanderthals to their physical environment.     

A new perspective on Late Holocene social interaction in Northwest Alaska: results of a preliminary ceramic sourcing study

This research examines the evidence for prehistoric ceramic exchange networks over the last 2000 years in northwest Alaska through the use of neutron activation analysis of ceramic artifacts. Results from ceramic analysis on eight coastal and inland archaeological sites identified three source macrogroups and three associated subgroups. Clay source diversity and shared source macrogroups between geographically distant sites suggest the use of multiple sources and/or the movement of pots between production locales, mirroring related patterns in pottery stylistic data. Although additional analytical work is needed to fully understand the changing character of clay procurement and ceramic distribution across this time period, this study provides exploratory data on past ceramic production and distribution that hints at changes in exchange and territoriality in northwest Alaska during the late Holocene.     

Late Holocene climatic fluctuations and soil genesis in southern Patagonia: effects on the archaeological record

Geoarchaeological research conducted at five localities in southern Patagonia and Tierra del Fuego identified a mollisol within late Holocene aeolian and colluvial deposits associated with archaeological material. The mollisol's origin and development are related to an increase in humidity (c. 1000 BP) following an episode of severe drought during the Medieval Warm Period. Corroborating data is supplied from dendroclimatic and pollen studies. A drastic reduction in frequency of artefact distribution recorded at the sites studied corresponds to this pedologic event, suggesting a greater human presence at these sites during earlier, regional-scale arid conditions. However, the paucity of archaeological remains may also be the result of the low resolution of cultural evidence following the pedologic development due to superimposition over previous archaeological deposits.     

Seasonal fluctuations in diet and death during the late horizon: a stable isotopic analysis of hair and nail from the central coast of Peru

The goal of the isotopic analysis of hair and nail from Puruchuco-Huaquerones is to reconstruct short term paleodiet using the stable isotopes of carbon and nitrogen in one centimetre increments of hair and two discrete points (distal and proximal) on the nail. This sampling method allows for the reconstruction of diet on a monthly basis (hair) and also diet at two periods (nail): four months and two weeks antemortem. The analysis of these two tissues demonstrates that diet varied from month to month and that food was not stored in any significant quantity. The patterning of the isotope data appears to be closely tied to the agricultural cycle, although a vertical economy cannot be rejected as an alternative explanation. Isotope data for both short (e.g., hair and nail) and long term diet (e.g., bone) are similar; this is interpreted as evidence for the continuity of the settlement in this area. There are no significant differences in the season of death between males or females or between the winter and summer months. The slightly higher mortality rate in the summer may be due to crop failure and subsequent food shortages.     

Mortality analysis of the Late Pleistocene bears from Grotta Lattaia,central Italy

Reported here are the results of a mortality analysis of an Ursus spelaeus death assemblage from Grotta Lattaia, southern Tuscany (central Italy), excavated in 1939. The Grotta Lattaia cave bears are among the latest representatives of the species. The large amount of cave bear remains indicates that the cavern was a lair for hibernating bears which repeatedly, but not necessarily yearly, occupied it. The mortality evidence indicates that deaths occurred primarily during hibernation from violent predation, and, therefore, that the bears had direct interaction with other carnivores. However, no sign of interrelation with humans could be found, even though Middle Paleolithic human remains and tools had been recovered associated with the bear material. Grotta Lattaia can be thus considered an example of cumulative, non-human-caused violent deaths in a hibernation context.     

Palaeoenvironmental reconstruction of La Olla,a Holocene archaeological site in the Pampean coast (Argentina)

The evolution of littoral palaeoenvironments in the southern Pampas region of Argentina towards the end of the early Holocene and the beginning of the mid Holocene is discussed, and the formation processes of the archaeological site of La Olla are analysed. This site is located in the intertidal zone of the present beach and is remarkably well-preserved. The human occupation at the site has been dated at between 7400 and 6480 yrs BP, and is interpreted as a place for the processing and consumption of the southern fur seal (Arctocephalus australis) and southern sea-lion (Otaria flavescens). It is concluded that biostabilization by microbial mats of the sedimentary structures and archaeological remains that developed and are present on the tidal flat prevented their erosion by wind, turbulence currents and waves. This is what has permitted the exceptional preservation of the site. On the basis of the analyses of one of the sectors of the site it can be concluded that the sedimentary succession of the La Olla site is the result of the coastal environmental changes during the early–mid Holocene in the pre-maximum transgressive episode. During this interval a tidal flat developed on the Pleistocene abrasion platform. Human occupation occurred during the formation of mixohaline marsh, an upper intertidal–lower supratidal zone ecosystem.