The Ecological and Cultural Effects of Clam Gardens on Northern Quadra Island, British Columbia

Clam gardens along the Northwest Coast of North America are the physical remains of traditional mariculture practices. On northern Quadra Island, British Columbia, the dense concentration of clam gardens and associated large shell middens reflect the cultural importance of clam harvesting. Spatial analysis of clam gardens demonstrates this importance, as clam gardens represent 15.5 hectares (ha) of clam habitat surface area, and building the gardens increased the surface area of clam habitat by up to 8.3 ha (54%). Microscopic analysis of butter clam (S. gigantea) shells over a 11,500-year period provides a long-term history of clam growth. These data suggest that with the exception of the late Pleistocene, there is little difference in clam growth throughout this time. Thus, increasing clam habitat, rather than the effects of tilling, controlled harvesting, or changing substrate, is the single largest benefit to overall clam production.