Document ID: chunk:federal_register_of_legislation:F2019L00106:body:0:p38
Version: federal_register_of_legislation:F2019L00106
Segment Type: other
Provision Reference: 
Character Range: 100841–103892

native fish species (Cadwallader 1978; 1979; Lintermans 1991a; ACT Gov 1999; Horner 2000; Burton et al., 2004). Silt and clay particles can absorb, transport and store metal contaminants (Stone & Droppo 1994) so that deposited sediments act as a sink for heavy metals, with contaminated sediment potentially continuing to pose a pollution problem long after land disturbances first occurred (Trimble 1981; Mol & Ouboter 2004). Large geomorphic impacts have been observed in Hughes Creek where important habitats for Macquarie perch, including riffles, deep pools and instream woody habitats have been buried, leading to the formation of a uniform, wide, shallow-flowing sand bed stream (Kearns & Tonkin 2015; Erskine 2016).
High levels of suspended sediment will reduce light penetration leading to reduced primary productivity, submergent macrophytes, food and habitat availability for fish (Edwards 1969; Petts 1984; Power 1984; Brookes 1986; Van Nieuwenhuyse & LaPerriere 1986; Schälchli 1992; Davies et al., 1992; Richards & Bacon 1994). Suspended sediments may impact fish directly by clogging gill rakers and gill filaments leading to death (Bruton 1985). Suspended sediment will also affect the efficiency of hunting, particularly in the case of visual feeders (Vinyard & O'Brien 1976; Bruton 1985; Ryan 1991) and may also affect spawning success of fish by rendering visual courtship signals less effective (Burkhead & Jelks 2001).
In addition to sedimentation, snags (woody and rocky) have a critical role to play in the ecological functioning of rivers. Snag structures can consist of whole trees, limbs, root masses, boulders and rocks that are partly or totally submerged. Snag structures provide complex and diverse habitat for native fish and invertebrates including cover from predation, refuge from high velocity flows and feeding sites (Bilby & Likens 1990; O'Connor 1991; Crook & Robertson 1999; Treadwell et al., 1999). Snags also play a significant role in promoting different habitat elements including scour pools, bars, islands, and side-channels. Conversely removal of snags can lead to a range of detrimental effects on stream morphology including increased flow velocity, bed degradation, channel enlargement and direct loss of fish habitat (Erskine & Webb 2003). In general, associations between instream woody habitat are much stronger for fish occupying more lowland waterways, such as Murray cod (Maccullochella peelii), compared to those occupying smaller, more upland waterways (Tonkin et al., 2016c). However, strong positive associations were recently reported between the abundance/biomass of Macquarie perch in Hughes Creek and instream woody habitat, riparian vegetation and water depth (Tonkin et al., 2016c).
Since the mid 19th 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,