Broken River Rehabilitation project: Summary survey of Fish and Macroinvertebrates (June 2006 to May 2007)

"June 2007".

Project Number: Improving Flow and Habitat in the Broken River: Monitoring of lnstream Habitat - M/BUS/105.

MDFRC item.

Phase 2 of Broken River Rehabilitation Project (see final report 2008), plus fish monitoring phase (see Summary report 2009) and (Final report 2009), plus Phase 1 of Broken River Restoration Project (see Phase 1- Site selection report) and (Phase 1 – Scoping Report).

The presence (or absence) of large woody debris (LWD) within lowland river channels is a major driver of both primary productivity and community structure of fish and invertebrates as well as other associated biota (Nicol et al 2002). In Australian lowland rivers the substratum generally consists of sand, silt or clay. In general these substrates are colonized by few invertebrates (Humphries et al. 1998). The principle substratum for biofilm development and macroinvertebrate colonization is large woody debris (Crook and Robertson 1999). Large woody debris supports a more diverse invertebrate community in comparison to other instream sediments (Humphries et al. 1998; Growns et al. 1999) and increases instream habitat complexity (Pusey and Arthington 2003). The presence of LWD influences fish habitat at a number of scales. The number of fish in a river is often related to the quality and heterogeneity of instream habitat (Koehn and O’Connor 1990). The presence and complexity of LWD assists in the creation of scour pools and slackwaters promoting habitat diversity for fish and refuge from flow and predators. Fish communities in streams with a poor diversity of habitat are usually dominated by fish species that are tolerant of a wide variety of habitats. These generalists are most often introduced species (Koehn and O’Connor 1990) which compete with native fish species for food resources. Between 1960 and 1975 "River improvement" works were carried out in the Broken River in an effort to decrease the frequency of flooding. Works undertaken included the construction of levees and removal of LWD. In 2006 work was commenced to re-snag the Broken River. This report summarizes data from a fish and macroinvertebrate surveys undertaken prior to the commencement of this work and the monitoring following the introduction of the snags.