Through the case of salmon population science in the Columbia River Basin, this article explores how political mobilizations can sometimes use quantitative analysis of populations in unexpected ways. In the Columbia River, both fish counting and such controversial concepts as carrying capacity have served as tools not only for conservation advocacy but also, at times, for probing histories of settler colonialism and building alliances across difference. By examining the unusual case of salmon tallying and research in this region, this article argues that while population biology has been repeatedly used within problematic and even violent state projects, in certain contexts it can also become a practice of multispecies noticing and a catalyst for new coalitions. Based on this example, the article raises broad questions about what renewed attention to population biology might contribute to the growing subfield of more-than-human anthropology. It argues that anthropologists have not paid enough attention to the possibilities for numbers and population concepts to positively contribute to movements for more livable worlds. In light of this example, this article aims to foster additional anthropological attention to the situated and context-specific politics of scientific practices and tools.