Background/Aims: Movement is a key driver of the distribution of animals and the structure of populations, communities, and ecosystems. Habitat loss and fragmentation can compromise movement and contribute to population declines. However, there is often insufficient knowledge about when, why, and where animals move, particularly in highly modified environments.
Methods: We present results from a 15-year study of the movement behaviour of Murray Cod in a highly modified floodplain ecosystem in the lower Murray River. We use acoustic and radio telemetry to assess movement within and between different habitat types and survival. We analysed movement data to identify the key environmental conditions associated with movement, the influence of and how a new regulating structure can be managed to influence movement behaviour, the role of movement on recovery following a hypoxia induced fish kill event, and how such knowledge has filled key knowledge gaps regarding broader population dynamics in the region.
Results and Conclusion: Movement within and between an anabranch and main river channel habitats increased during the core spawning period and during elevated discharge. The likelihood of Murray cod moving to an anabranch system from the Murray River declined substantially following construction of a new flow regulating structure (a weir and vertical slot fishway). Managed flows delivered through the anabranch after regulator construction in accordance with recommendations on time-of-year and magnitude of discharge, increased the movement of adult fish within and between habitats. During the study, a hypoxic event caused high mortality but also resulted in a high proportion of fish migrating outside of the study reach, before returning to the system over several years. Monitoring the reach occupancy and movement behaviour of juvenile fish following this event also provided important information on recovery pathways and broader population dynamics in the region. These results demonstrate how flow management can help a keystone species access habitats required to complete critical life history requirements including recovery from disturbance events. Importantly, the work provides an example of how timely and robust applied research has informed a major intervention program aimed at enhancing ecological outcomes