Document ID: chunk:federal_register_of_legislation:F2019L00106:body:0:p39
Version: federal_register_of_legislation:F2019L00106
Segment Type: other
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Character Range: 103608–106673

Century, thousands of snags have been removed from Australian streams and rivers, especially within the Murray-Darling Basin, in an effort to stabilise rivers (Erskine 1990; 1992; 2001) and to increase river navigability, flood mitigation and increase channel efficiency (Gippel 1995, Erskine & Webb 2003). In Victoria, recent instream woody habitat volumes have been found, on average, to be 41 per cent lower than reference levels (Tonkin et al., 2016b). Given the objectives of such works, including navigation, flood mitigation and channel efficiency, it seems likely that the most intensive snag removal programs concentrated on lowland reaches, likely within stretches of rivers in the southern Murray-Darling Basin where Macquarie perch were present.
Therefore in the short term resnagging is necessary in specific areas, while in the longer term the restoration of riparian vegetation is essential to ensure future supplies of snags. Resnagging some areas of riverine habitat has been recommended as an action under other national threatened species recovery plans (Brown et al., 1998; NMCRT 2010). A works program established and initiated in 2008 in Holland's Creek whereby "rock-seeding", riparian re-vegetation, rock-bar installation and the insertion of snags into the creek aimed to increase habitat availability and complexity and provide refuge for native fish (Raymond & Ryall 2017a).
In streams degraded by sedimentation and sand slugging, natural debris which once would drop into channels and provide shelter and refuge for invertebrate food items for Macquarie perch, is swallowed by the sand or swept away due to a lack of branches and logs that can hold debris in water (Schetzer 2017). Recent trials undertaken at Hughes Creek using in-stream installations of paired garden stakes led to an increase in invertebrate densities and diversity (Schetzer 2017). The novel technique presents a low-cost, low-maintenance option for habitat improvement for native fish which feed on them, like Macquarie perch.
Riparian vegetation is important to freshwater fish like Macquarie perch as it can help conserve freshwater biodiversity by re-establishing linkages between riparian systems and stream fish (Pusey & Arthington 2003). The interception of terrestrial sediments and nutrients by the riparian zone has important consequences for stream fish, maintaining habitat structure, water clarity and food-web structure (Pusey & Arthington 2003). A study in Hughes Creek found that Macquarie perch preferred areas within pools that were shaded by overhanging riparian vegetation (ARI 2007). Riparian re-vegetation of areas where Macquarie perch occur, or may potentially occur, is recognised as an important conservation action (Erskine 2016).

6.2.2 Introduced fish species
Introduced fish species may impact on native species in a number of different ways such as: predation (particularly on eggs and larvae); competition for habitat and food resources; habitat degradation; spread of diseases and parasites. Interactions with introduced fish species