Small-scale movement and migration cues of Australian bass (Percalates novemaculeata) in an urbanised river

Urban river catchments are often severely affected by human activities but may still retain significant biodiversity. Surprisingly little is known about the behaviour of urban fishes, even those popular with anglers. Key environmental variables that trigger fish behaviour, such as river flow, are highly affected by instream structures including weirs and changes in the natural flow regime. Here, we used acoustic telemetry to examine the movements of Australian bass in a river located in suburban Sydney, Australia. We found that fish tended to be nocturnally active, however, small-scale movements were highly idiosyncratic and less associated with river flow than other factors. Larger-scale movements associated with spawning migrations were strongly correlated with winter floods. Half of the tagged fish migrated to the confluence of the river with Sydney Harbour to breed. Their return migration was hampered by a weir, but the provision of a new fish way facilitated successful return to freshwater at high tide. Despite occupying a highly affected, urban catchment fish behaviour showed similarity to those occupying more natural drainages. Our results highlight the importance of maintaining natural river flows in urban catchments and sustaining fish movement and migration capabilities through the installation of appropriate fish passage devices.