Kirsten Rowell

Ancient Clam Gardens Increased Shellfish Production: Adaptive Strategies from the Past Can Inform Food Security Today

Maintaining food production while sustaining productive ecosystems is among the central challenges of our time, yet, it has been for millennia. Ancient clam gardens, intertidal rock-walled terraces constructed by humans during the late Holocene, are thought to have improved the growing conditions for clams. We tested this hypothesis by comparing the beach slope, intertidal height, and biomass and density of bivalves at replicate clam garden and non-walled clam beaches in British Columbia, Canada. We also quantified the variation in growth and survival rates of littleneck clams (Leukoma staminea) we experimentally transplanted across these two beach types. We found that clam gardens had significantly shallower slopes than non-walled beaches and greater densities of L. staminea and Saxidomus giganteus, particularly at smaller size classes. Overall, clam gardens contained 4 times as many butter clams and over twice as many littleneck clams relative to non-walled beaches. As predicted, this relationship varied as a function of intertidal height, whereby clam density and biomass tended to be greater in clam gardens compared to non-walled beaches at relatively higher intertidal heights. Transplanted juvenile L. staminea grew 1.7 times faster and smaller size classes were more likely to survive in clam gardens than non-walled beaches, specifically at the top and bottom of beaches. Consequently, we provide strong evidence that ancient clam gardens likely increased clam productivity by altering the slope of soft-sediment beaches, expanding optimal intertidal clam habitat, thereby enhancing growing conditions for clams. These results reveal how ancient shellfish aquaculture practices may have supported food security strategies in the past and provide insight into tools for the conservation, management, and governance of intertidal seascapes today.

Ancient Shellfish Mariculture on the Northwest Coast of North America

While there is increasing recognition among archaeologists of the extent to which non-agricultural societies have managed their terrestrial ecosystems, the traditional management of marine ecosystems has largely been ignored. In this paper, we bring together Indigenous ecological knowledge, coastal geomorphological observations, and archaeological data to document how Northwest Coast First Nations cultivated clams to maintain and increase productivity. We focus on “clam gardens,” walled intertidal terraces constructed to increase bivalve habitat and productivity. Our survey and excavations of clam gardens in four locations in British Columbia provide insights into the ecological and social context, morphology, construction, and first reported ages of these features. These data demonstrate the extent of traditional maricultural systems among coastal First Nations and, coupled with previously collected information on terrestrial management, challenge us to broaden our definition of “forager” as applied to Northwest Coast peoples. This study also highlights the value of combining diverse kinds of knowledge, including archaeological data, to understand the social and ecological contexts of traditional management systems.

Coastal Adaptations During the Archaic Period in the Northern Sea of Cortez, Mexico

ABSTRACT This article integrates geological, biological, ethnographic, and archaeological lines of evidence to reconstruct fishing patterns between approximately 4100 and 500 BC in the northern Gulf of California. In addition to shell collecting along the coast, several species of fish were captured, mainly endemic sciaenids of the upper gulf. Our study focuses on the northern Sonoran coast where recent archaeological studies have discovered scores of otoliths (fish ear bones) in archaeological contexts. We report the species composition (chano, corvina, totoaba) and relative size of the prehistoric catch and discuss the modern biology of these species known to inhabit this area. Our evidence suggests that this area offered an important resource for Archaic hunters and gatherers who were drawn here to exploit fish at certain times of the year. Following sea level stabilization around 6,000 years ago, particular geomorphic settings provided opportunities to easily harvest large quantities of fish by spearing, netting, or hand catching them.