Use of radiotelemetry to quantify diel habitat preferences and minimum environmental flow requirements of a tropical riverine fish (Sooty grunter Hephaestus fuliginosus)

<p dir="ltr">Quantitative relationships between river discharge and hydraulic habitat availability for key taxa are important elements of environmental flow assessment. </p><p dir="ltr">We used radiotelemetry to examine diel patterns of habitat use by tracking the locations of 17 juvenile Sooty grunter (Hephaestus fuliginosus) over a 10-day period during the late dry season in a river in the wet–dry tropics of northern Australia. Habitat use data were integrated with a hydrodynamic model to identify preferred hydraulic habitat and explore different river discharge scenarios to assess the potential effects of water abstraction on habitat availability. </p><p dir="ltr">Sooty grunter exhibited a strong preference for shallow, fast flowing mesohabitat (riffles and runs). Hydraulic microhabitat preference was modelled using generalised additive mixed-effect models (GAMMs) and showed no significant difference in microhabitat selection between day and night. Habitat criteria developed from a combined day-night GAMM were defined as locations with velocities of 0.26–1.42 m s−1 and depths <0.69 m. Hydrodynamic modelling of river discharge scenarios in the study reach showed that the area of preferred habitat was highest at 8 m3s−1, with large declines in habitat area under low flows (61% decline in habitat area at 0.5 m3s−1 compared to the discharge of 2.8 m3s−1 at the time of radio-tracking). </p><p dir="ltr">While the study focusses on a single species, our findings demonstrate the broad applicability of radiotelemetry as a means of quantifying the diel hydraulic habitat requirements of riverine fish to support the objective determination of environmental flow regimes.</p>