Does the reintroduction of large wood in a large dryland river system benefit fish assemblages at the reach scale?

Abstract

Benefits of reintroduced large wood in river channels are largely based on studies at site scales in high-energy systems. By comparison, relatively little is known of the benefit of reintroduced large wood in low-energy systems at larger, reach scales. The present study assessed the effects of reintroducing large wood on fish assemblages along the Barwon–Darling River, Australia. Fish were sampled in replicated reaches subject to three treatments: six reference (wooded), six control (unwooded) and six managed (wood reintroduced) reaches. Sampling was conducted before and several months after wood addition, and then during a period following several large floods. Results demonstrate that reintroducing large wood had limited effects on fish. There were significant differences between treatments in fish length, but not in total abundance or species composition between treatments. Significant differences were detected in total abundance, species composition and fish length over time. There was an interaction recorded between treatments and time for fish length, but not total abundance or species composition. It is suggested that the lack of response by fish was because the physical character and position of the reintroduced wood pieces did not replicate ‘natural’ reference conditions. However, high variability in fish assemblages through time, likely in response to hydrological variation, reduced the power of the study to detect differences between fish over the shorter time period of the study (<5 years).