One CSV file with data from basic field surveys of southern sea otters at five sites in California, USA, including (from north to south) Elkhorn Slough, Monterey, Big Sur, Piedras Blancas, and San Luis Obispo, are provided. These are the data used to fit models in Law et al. 2024 (full citation in the larger work) publication in Science. The data consist of otter age, sex, and size morphometrics, measured from sea otter captures; associated forage information collected by visual surveys; and hardness of forage prey species. Complete description of the study objectives, methods, field sites, and uses of these data for analyses and interpretations can be found in Law et al. 2024. Although it is well documented that tool use can enable the utilization of novel resources, the fitness benefits associated with this innovative behavior are difficult to test. Using longitudinal data from 196 radio-tagged southern sea otters, we found that individuals, particularly females, with frequent tool use gained access to harder, larger prey items. In turn, the mechanical advantages of tool use during food processing translated to reduced tooth damage in tool users. We also found that tool use diminishes trade-offs between access to different prey types, tooth health, and caloric intake that are highly dependent on the relative availability of prey in the environment. Overall, tool use allows individuals to maintain caloric requirements through the processing of alternative prey that are otherwise inaccessible without the use of tools, indicating that this innovative behavior is a necessity for the survival of southern sea otters in environments with depleted preferred prey.