Abstract
Despite providing considerable benefits to society, dams and weirs threaten riverine ecosystems by disrupting movement and migration of aquatic animals and degrading riverine habitats. Whilst the ecological impacts of large dams are well studied, the ecological effects of low-head weirs that are periodically drowned out by high flows are less well-understood. Here we examine the effects of a low-head weir on fine- and broad-scale movements, habitat use, and breeding behaviour of three species of native freshwater fish in the Nymboida River in coastal eastern Australia. Acoustic telemetry revealed that eastern freshwater cod (Maccullochella ikei) and eel-tailed catfish (Tandanus tandanus) made few large-scale movements, but Australian bass (Percalates novemaculeata) upstream of the weir were significantly more mobile than those below the weir. Within the weir pool, all three species displayed distinctive patterns in fine-scale movement behaviour that were likely related the deeper lentic environment created by the weir. No individuals of any species crossed the weir during the study period. Tandanus tandanus nesting behaviour varied greatly above and below the weir, where individuals in the more lentic upstream environment nested in potentially sub-optimal habitats. Our results demonstrate the potential effects of low-head weirs on movement and behaviour of freshwater fishes.
Highlights
Despite providing considerable benefits to society, dams and weirs threaten riverine ecosystems by disrupting movement and migration of aquatic animals and degrading riverine habitats
This study focuses on the movement behaviour of three species of freshwater fish: eastern freshwater cod (Maccullochella ikei), freshwater catfish (Tandanus tandanus), and Australian bass (Percalates novemaculeata)
In the downstream linear array, M. ikei were detected on average for 81.43 ± 16.37 (S.E.) days, P. novemaculeata were detected 78.5 ± 13.5 days and T. tandanus were detected for 52.33 ± 21.79 days (Fig. 3)
Summary
Despite providing considerable benefits to society, dams and weirs threaten riverine ecosystems by disrupting movement and migration of aquatic animals and degrading riverine habitats. Whilst there is much focus on large instream structures, such as dams, low-head weirs that periodically drown out can significantly alter aquatic habitat by changing river hydraulics[6] and by acting as a significant barrier to movement[7,8], if drown-out events are short-lived and/or unpredictable. An ecological barrier is formed immediately upstream of physical barrier, where the hydraulic characteristics (e.g. water velocity) that stimulate and help orient fish movements are altered[20]. In this case, habitats become lentic and may be more akin to non-riverine, lacustrine environments, which can affect fish behaviours at the local-scale[14]. The reservoir created by a barrier may alter or delay abiotic cues, such as water temperature or river discharge, to reproductive behaviours in fish, and may alter suitable nesting habitat for some species
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