The giant otter is an endangered South American carnivore with a facultatively cooperative social system that may be affected by local ecology. This chapter synthesises demographic data arising from a 16 year study of a population inhabiting patchily distributed and resource-rich oxbow lakes in the floodplain of Manu National Park, in the Department of Madre de Dios, Peru. It explores how giant otter group size and composition relates to territory size, and how reproductive success is affected by territory quality. The chapter concludes with a discussion on the implications of these findings for giant otter conservation in southeastern Peru, in the face of increased human/giant otter conflict; tourism; and mining, logging and agricultural pressures, and highlights the need for a giant otter habitat conservation corridor along the Madre de Dios River.