Ancestral sea gardens supported human settlements for at least 3,800 years on the Northwest Coast of North America

Abstract

The relationships between clam gardens and human settlement throughout the millennia reflects the inseparable links among human demographics, marine management systems, and the social-ecological contexts in which they are embedded. However, it can be difficult to assign causation between the initiation and development of eco-cultural innovations like clam gardens and the proliferation of human societies due to the temporal uncertainties associated with both. Here, we bring together data on the shape of the local relative sea level curve, clam garden wall elevation as determined by GIS and drone imagery, radiocarbon dates of clam garden walls, and ecological and archaeological field observations, to assign proxy ages for the clam garden walls of different tidal heights in Kanish and Waiatt Bay on northern Quadra Island, British Columbia, Canada. These data, combined with our mapping and dating of settlement sites, demonstrate a temporal relationship between clam garden building effort and the densification of human settlements. In Kanish Bay, where we have high resolution data, clam gardens begin to be constructed in significant numbers at least 3,800 years ago; this corresponds to a time of increased establishment of large human settlements. The corresponding increase in settlements and clam gardens reflects both the need to increase sustainable food production and the larger number of people who could sustain the ecological and social foundations of the production system. The correlation between number and area of clam gardens and the number of new, large settlements continues until ∼2000 years ago. After this time, existing settlements increase in size, but no additional large settlements were established. New clam gardens continue to be built but in seemingly lower numbers. This shift in settlements and clam gardens suggest that a threshold in social-ecological carrying capacity may have been reached in this land- and seascape. In the last few centuries, there is a dramatic decline in the number of clam gardens and evidence of human settlement, corresponding to social and ecological changes associated with European colonization. Taken together, these data demonstrate the strong linkages among Indigenous peoples, their lands and seas, and resilient food systems over the millennia.

Disrupting and diversifying the values, voices and governance principles that shape biodiversity science and management

“…Similarly, the construction of intertidal rock-walled terraces created clam gardens known to double clam production [ 31 ]. These intertidal innovations required re-engineering to adapt to changing sea-levels [ 32 ]. Size and sex selective fishing practices for Pacific salmon, enacted at river mouths with wooden weir and stone trap technologies, sustained salmon productivity and resilience to climatic disturbances for thousands of years [ 33 , 34 ].…”

Can fisheries be “regenerative”? Adapting agroecological concepts for fisheries and the blue economy

“…High tides deposit sand and other substrate on the shoreward side of the wall, increasing the amount of habitat available for clams and other species (Lepofsky et al 2020). Historically, clam gardens are a technology used to diversify and increase food production, one that historically scaled with population growth while not causing environmental degradation (Holmes et al 2022). While they have some features of a coerced system, for example, the effort taken to create and maintain the rock walls to favour a specific food resource, the gardens have been shown to not only increase clam productivity but also contribute positively to adjacent biodiversity and ecosystem structure (Cox et al 2019;Cox 2021).…”