In the Murray-Darling Basin, common carp (Cyprinus carpio) is a significant pest species that is associated with numerous ecosystem impacts. Knowledge of the species ecology, including movement, is critical to interpret and predict responses to infrastructure and water management, and inform control measures. In the highly regulated lower River Murray, few studies have focused on the spatial ecology of common carp, particularly in association with high river flows.
We used acoustic telemetry to investigate the movement of common carp in the lower Murray River from August 2021–March 2024, a period characterised by high flows and extensive floodplain inundation. Of 220 tagged fish, 211 (96%) were detected for periods up to 944 days, with movements from tagging locations spanning from 460 km downstream to 1145 km upstream. Although many individuals occupied limited linear ranges, over half the tagged fish exhibited movements ≥50 km, predominantly in an upstream direction and most frequently during high flows in spring–summer. Large-scale movements included transition among the Murray and Darling rivers, and among distant reaches of the Murray River. For these individuals, movements were often followed by apparent establishment of new home ranges, although a substantial proportion (~20% of detected fish) also undertook homing movements to their original tagging locations. The use of off-channel habitats was extensive, with ~75% of tagged fish detected in major anabranches of the lower River Murray, particularly during flooding.
Common carp demonstrated considerable plasticity and variability in spatial scales of movement. Under conditions of high flow, inter-regional movements, as well as homing, were common. Our findings inform river management at multiple scales, including the operation of floodplain infrastructure and potential spread of biocontrol agents such as CyHV-3.