Snapper is one of Australia’s most significant fishery resources and so has attracted considerable research and management focus. Yet, throughout the 2000s, Snapper fisheries in several State jurisdictions experienced significant downturns. Particularly in South Australia from the mid-2000s, there were significant declines in catches and stock status. Consequently, in November 2019, fishery closures were imposed to Snapper fishing across most of the State’s coastal waters. This talk investigates the population declines. The fishery catches during the 2000s were assessed in a broad historic context, by comparing with those sustained previously. The demographic processes that drive the population dynamics were identified from long-term biological datasets derived from market sampling. Furthermore, movement, connectivity and stock structure were determined from otolith chemistry studies. Extensive fishery and biological datasets were integrated in a computer fishery model that estimated time series of biomass and recruitment rates for several stocks. Natural variation in biomass of Snapper populations reflected spatial and temporal aspects of 0+ recruitment and subsequent redistribution of fish through density-dependent adult movement. Recent declines for the two stocks that are closed to fishing are attributable to numerous contiguous years of poor recruitment and simultaneous high levels of extraction of adult fish by the fishery.