Population structure of adult female Australian sea lions is driven by fine-scale foraging site fidelity

► mtDNA and stable isotope data were collected across 17 breeding colonies of Australian sea lions. ► Isolation by distance was significant at 40 km. Alternative foraging ecotypes were present at most sites. ► Fine-scale foraging site fidelity may restrict migratory movement. ► Foraging behaviour is not maintained along matrilines. ► Social learning could maintain foraging behaviour over generations.