title: Bivalve growth-stages as a measure of harvesting intensity: application on the Southern Northwest Coast
Creators: name: Pierce, Shona Dejeanne
Publisher: name: Western Washington University
Year: 2011

description: <p>Prehistoric settlements along the Pacific Northwest Coast have produced some of the clearest records for study on human subsistence use, such as harvesting practices (Butler 2000; Cannon et al. 2008; Croes 1992; Moss 1993; Wesson 1988). The archaeological and ethnographic records in this region have produced artifacts and oral accounts that have led scientists to logical conclusions about specific types of subsistence use. In turn, subsistence use data can tell us many things about a society, including population size, longevity of settlement and site function. Intensities in subsistence practices can also show whether an area was used as a long-term, or sedentary site or a short-term, task-specific site. Evidence of subsistence use, particularly shellfish consumption, has the potential to help lead us to new conclusions regarding settlement types. This evidence enables researchers to come closer to pinpointing the time when prehistoric Pacific foragers began moving toward collector societies who actively managed their subsistence resources - "conservationism;" and provides us the opportunity to learn about specific methods those societies used to sustain growing human populations in semi-permanent settlements. The Pacific Period (5500 BP-contact) marks the transition from archaic, mobile foragers to semi-sedentary, collector societies. Four cultural phases comprise the Pacific Period; they are the St. Mungo, Locarno Beach, Marpole and Strait of Georgia phases. Each cultural phase is characterized by unique innovations in subsistence economies and settlement patterns. Archaeological evidence of these innovations helps to pinpoint what point in time foragers practiced resource management. Shellfish maturity ratios have only recently been considered by archaeologists as a means of analyzing prehistoric harvest intensities and settlement types. Recently, Cannon and Burchell (2009) proposed a model for relating shellfish age at death, measured by growth rings, to broad scale residency patterns and harvest pressures at Hunter Island and Namu, British Columbia, Canada. Based on the assumption that management of local resources would be necessary for residential occupation, senile-stage shells should comprise a larger proportion of midden in long-term village sites, as people will act to preserve the resource for future use. Working on the same assumption, a mixture of mature and senile shells will reflect short-term, task-specific encampments, as people residing in areas for short periods of have no future tie to extraction sites. Further maturity stage analysis is limited, however, as Cannon and Burchell's studies of the association between shell maturity ratios and harvest intensities focus on a single clam species (Saxidomus giganteus), and is largely unexplored in other parts of the Northwest Coast. An analysis of Protothaca staminea growth stage profiles from 45SK46 at Deception Pass and 45WH55 at Woodstock Farm, Washington, tested whether or not the shells of other species can illustrate the same relationship evident in Cannon and Burchell"Ÿs model. Results of this analysis suggest that aggregated data from P. staminea maturity stage proportions could be used to determine general site type classifications. It was determined, however, that minute sub-level changes within the stratigraphy of the site were lost when the raw data was lumped together, making sites appear static. Sub-level analysis of maturity stages was necessary to track maturity patterns and changes in settlement type across time. This refined methodology greatly clarified the contextual timeframe of the sampled units, showing clear breaks in maturity stage ratios within the levels that would otherwise be unobserved. Results from the two sites explored within this study showed fluctuating ratios of senile:mature shells by sub-level deposition. During the 300-year time span at site 45SK46, a gradual decline in mature clams is observed. Toward the latest periods of site occupation, however, there was a resurgence of mature clams, which suggests renewed interest in harvesting clams. These fluctuations in sub-level maturity stage ratios are suggestive of alternating short- and long-term site use. These patterns may also suggest active shellfish management by prehistoric societies. Results from 45WH55 exhibit similar fluctuations in shellfish maturity stages. In analyzing the units within 45WH55, it was observed that the north and south halves of the site are functionally distinct from each other in terms of harvest practices. Campbell et al. (2010) similarly found that the two halves of the site were distinct in that the northern portion of the site contained evidence of pithouse and hearth features, while the southern portion contained features geared towards lithic, butchery and secondary refuse activities. The classification of clam maturity stages through growth stage analysis provides substantial evidence supporting conclusions drawn from pre-existing faunal remains and seasonality analyses that classify both study sites as short-term, task-specific encampments. The association between settlement type and P. staminea maturity patterns evident in the two sites of this study supports Cannon and Burchell's model of growth stage analysis on S. giganteus. The correlating results between Cannon and Burchell's study and this study suggest that their maturity stage model could be applied to archaeological sites outside of central British Columbia, and could also be used across shellfish species.</p>