A spatially-explicit approach for the research and management of in-channel fish habitats in large dryland rivers
In many floodplain river systems throughout the world, the destruction of habitat continues to be a major threat to fish populations. An essential prelude to effective river conservation and rehabilitation is being able to characterise how the spatial arrangement of habitats shape the composition and distribution of fish assemblages. Concepts of landscape ecology, which can be used to analyse the role of spatial patterns in determining biological and physical processes over various scales, offer a sound basis with which to research and manage fish and their habitats in large rivers. Unfortunately, practical applications of these concepts remain isolated. Approaches are typically applied at single scales, sampling small sites widely spaced within the river, which are then assumed to be representative. Single scale research lacks the spatial resolution necessary for detecting patterns in fish–habitat associations across a range of spatial scales, greatly hampering attempts to determine threatening processes and develop viable strategies for river rehabilitation. Instead, there appears to be merit in using multi-scale approaches that simultaneously investigate small, intermediate and large spatial scales in large rivers.
At present, there is no set of principles for the assessment of fish habitats in the large dryland rivers of the Murray-Darling Basin, despite that fact that they account for 83% of all lowland rivers in Australia. Using recent research from the Barwon-Darling River it is demonstrated how principles in landscape ecology offer an effective way of researching fish-habitat associations in large dryland rivers. Evidence presented, shows that large dryland river habitats are spatially complex, displaying properties of discontinuities, downstream patterns of change and interconnected patches. Fish respond to this pattern differently at different spatial scales, and it is essential to understand these processes when attempting to reinstate habitat structure to rivers. The variable nature of flow in dryland rivers create an ever-changing pattern of habitats. River regulation impacts on this dynamic mosaic and therefore is likely to reduce the diversity of fish habitats.