Ten Years of Fishway Detections Reveal Species‐Specific Flow and Temperature Cues for Upstream Migration in a Regulated River

ABSTRACT

River regulation has disrupted flow regimes that promote fish movement, contributing to population declines. Restoring hydrological cues through managed environmental flows can support recovery yet requires understanding how river flow drives movement. We analysed 10 years (2014–2024) of passive integrated transponder detections at 11 consecutive fishways spanning 600 km of the lower Murray River, south‐eastern Australia. Upstream movements comprised 799 native golden perch ( Macquaria ambigua ), 69 native silver perch ( Bidyanus bidyanus ) and 199 non‐native common carp ( Cyprinus carpio ). All species showed significant non‐linear responses to discharge, albeit with wide confidence intervals, with movement probability increasing from ~0.1 at 4000 ML day ⁻¹ to 0.22–0.27 at moderate flows (10,000–14,000 ML day ⁻¹ ). Responses diverged at higher discharge: Silver perch probability increased to 0.58 at ~33,000 ML day ⁻¹ and golden perch increased again to 0.19 at 45,000 ML day ⁻¹ , whereas common carp declined to 0.07. Golden perch exhibited high movement rates at both moderate and high discharge (17.1 and 18.0 km day ⁻¹ at 10,000 and 45,000 ML day ⁻¹ ), whereas common carp rates fell from 20.4 to 6.7 km day ⁻¹ across the same range; silver perch rates increased only weakly and non‐significantly. Movement probability peaked at 22°C, 18°C and 15°C for golden perch, silver perch and common carp, respectively, while upstream movement distances averaged 106, 119 and 148 km. These species‐specific response curves indicate that flows exceeding ~20,000 ML day ⁻¹ delivered within optimal temperature windows could enhance native fish movement, particularly silver perch, while coinciding with reduced probability of movement in common carp.