Salinity drives the distribution of a top-order predator, the tiger shark (Galeocerdo cuvier), in an inverse estuary.

Understanding how dynamic environmental processes influence the distributions of top-order predators is fundamental to assess top-down effects on ecosystems. Tiger sharks (Galeocerdo cuvier) are a large top-predator that can trigger trophic cascades and structure communities. However, the dynamic physical processes that influence the distributions of these animals in coastal systems are largely unknown. Here, we assess the environmental processes influencing tiger shark movements in the inverse estuary of Shark Bay, Western Australia, a shallow coastal embayment with salinities consistently above that of the adjacent ocean. We applied Bayesian generalized linear mixed-effects models to generate dynamic predictions of suitable habitat for tiger sharks in this region. These habitats were associated with dense and shallow seagrass beds and largely reflected the spatial variability of hypersaline water (< 40). Under future climate scenarios, coastal areas worldwide are predicted to experience inverse estuarine conditions. We anticipate that the physical processes that influence tiger shark distributions in this study will become applicable to numerous other species of gill-breathing fauna in coastal ecosystems across the globe.