Shells of Nacella magellanica are abundant in archaeological shell middens distributed along the Beagle Channel. In this study we analyzed the oxygen isotopic composition of shells of this species to obtain information on its seasonal exploitation patterns by hunter-gatherer-fisher groups in this region during the nineteenth century. Oxygen isotopic data from shells recovered from Lanashuaia and from some occupations of Túnel VII (both contact sites) indicate that N. magellanica was gathered in different seasons. Our data agree with fauna-derived seasonal reconstructions, and collectively these data provide more detailed economic scenarios. Comprehensive results confirm that in the nineteenth century, Yamana people continuously occupied the coast of the Beagle Channel by means of short-lived campsites.