Photo taken whilst sampling the diverse food web of coastal and estuarine sharks and rays. A seasonally dynamic estuarine ecosystem provides a diverse diet for sharks and ray. Managing riverine and coastal sharks and rays of northern Australia requires understanding local food webs, and the dynamic connectivity between rivers, estuaries and coastal waters. A study supported by the Marine Biodiversity Hub explored this moveable feast in the South Alligator River estuary by comparing stable isotope and fatty acid signatures between shark and prey species (in wet and dry seasons and along an environmental gradient of salinity). The food webs varied in time and place, and those upstream were the most diverse, with distinct seasonal prey/habitat associations. Most Speartooth Sharks and Northern River Sharks had similar freshwater and mid-river diets, while Bull Sharks and Australian Sharpnose Sharks had largely marine diets. Two findings requiring further exploration were that Bull Sharks had predominantly marine-based signatures, yet were captured 80 kilometres upstream, and that seasonal change was evident in prey species but not in individual sharks. Overall, the results demonstrated that spatial and ecological processes in rivers drive the food webs that support tropical sharks and rays, and environmental management decisions should consider the many habitats these species use during their lives.