Effective fisheries management relies on knowledge of animal movements. Indices of behaviour can be useful for interpreting catch-per-unit-effort data. The Giant Mud Crab (Scylla serrata) is a widely distributed estuarine crab that supports significant fisheries harvest. We tagged 18 adult Giant Mud Crabs with accelerometer-equipped acoustic tags to track their fine-scale movement, alongside high resolution environmental data (e.g., water temperature), in a temperate south-east Australian estuary. A hidden Markov model was used to classify movement data into discrete behaviours. We investigated the influence of environmental covariates on these behaviours. Our modelling identified periods of inactivity and foraging. Inactive periods were most common (79 %). Crabs were most likely to forage during low, incoming tides; while inactivity was more likely at high tide as the tide recedes. Model selection removed time (hour) of day and water temperature (°C) as covariates, indicating that they do not influence behavioural dynamics at the temporal scale investigated. Our results are consistent with Giant Mud Crab being an opportunistic scavenger and demonstrate a relationship between the tidal cycle and foraging that is likely to minimize predation risk while maximizing energetic efficiency.