A large-scale, hierarchical approach for assessing habitat associations of fish assemblages in large dryland rivers. Hydrobiologia
Boys, C.A. and Thoms, M.C., 2006. A large-scale, hierarchical approach for assessing habitat associations of fish assemblages in large dryland rivers. Hydrobiologia, 572: 11–31.
Recent fish surveys have identified a decline in freshwater fish populations in many Australian dryland rivers, pointing to the need for better environmental management of inland catchment systems such as the Murray-Darling Basin (MDB). The Barwon-Darling River a key component of the MDB and is home to six species of fish that are formally listed as either endangered or vulnerable. Other native species are often in low numbers in this river and evidence suggests that many more species may be threatened.
Managing the ecosystems of the MDB to arrest the decline in native fish stocks requires better understanding of the interactions between fish and their habitats, including the spatial patchiness of both habitats and fish assemblages. Unfortunately, reliable information is not available to river managers because most aspects regarding the habitat use of Australian fish species still remain poorly understood. Lack of research into this area is particularly lacking for semi-arid to arid (dryland) climatic regimes which make up 83% of Australia’s lowland rivers. River managers also lack the appropriate tools to assess fisheries resources in large dryland rivers because current designs for fish surveys are often conducted at large spatial scales that are inappropriate for detecting the patchiness of fish assemblages in inland rivers. Instead, a hierarchical sampling design was used to partition the river into distinct physical regions, river reaches within those regions and habitat types within the study reaches.
The survey involved electrofishing at six discrete habitat units (large wood, smooth bank, irregular bank, root matted bank, mid-channel and deep pool) located within several 10 km long river reaches. Study reaches were, in turn nested within four larger geomorphological zones that have been identified along the length of the Barwon-Darling River, giving a total of 12 study sites. The fish assemblage varied significantly between habitat types and at the larger river scale. Golden perch (Macquaria ambigua), Murray cod (Maccullochella peelii peelii) and common carp (Cyprinus carpio) were found to be strongly associated with large wood, but golden perch and Murray cod exhibited higher habitat specificity than carp. Bony herring (Nematalosa erebi) were more commonly found in shallow edgewater patches. At the river scale, a regional difference in the fish assemblage was found to occur at scales closely corresponding to functional process zones. These regional differences involve changes in the relative abundance of species rather than the addition or replacement of species.
The hierarchical framework used in this survey will improve the efficiency of fish surveys in inland rivers by better incorporating regional patterns in assemblage structure and fish habitat use. Using this framework, the scale-specific information on fish assemblage differences and fish-habitat associations can be used to more effectively identify priority areas for regional rehabilitation programs such as those currently being investigated for other inland rivers in NSW.