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Salmon are iconic keystone species across the northern Pacific and Atlantic basins. Salmon is also a prized human delicacy. Wild salmon populations have been decimated by a combination of overharvesting, dams, and water diversions. Efforts to increase salmon abundance through fish farming and hatcheries have failed to stem the decline, instead exposing wild populations to diseases, pests, and the debilitating genetic effects of interbreeding with partially domesticated farm escapees and hatchery releases (1). The plight of salmon is not unique. Preserving the genetic heritage of the many aquatic species now entering the food supply through aquaculture is a growing challenge. Breeding programs enhance commercially valuable traits but reduce genetic diversity. Yet the reservoirs of genetic diversity in wild aquatic populations become increasingly critical to their survival and adaptation as the warming …