3. The year in review
Resnagging evaluation downstream of Yarrawonga
The concept for this program grew from previous MDBC-funded research projects that investigated the movement and habitat requirements of fish by radio-tracking in the Murray River (the Pilot Snag project). One of the many critical findings of these projects is the dependence of certain fish species (Murray cod, Trout cod and Golden perch) on snags as instream habitat. Nearly all Murray cod reside within or at snags, and after their annual spawning migration almost all fish return to the same snag. The residency, site fidelity and homing behaviour documented by this project, in conjunction with the already understood significance of snags as velocity shelters and food providers, established beyond doubt the absolute dependence of these fish on snags. The Pilot Snag Project also quantified snag characteristics, distribution and abundance and provided a template for resnagging.
Photo: Dean Ansell
Resnagging is one of the more obvious habitat management actions highlighted in the NFS. Recent funding for resnagging of sections of the Murray River has seen this management option become a reality and provides an important chance to test and evaluate the benefits of resnagging. The effects of snag management have been widely studied overseas, where resnagging has been used as a habitat rehabilitation tool, and its viability has been established through on-ground experience. Since 2002, the Resnagging Evaluation Project has supported the evaluation of the sites that were resnagged below Yarrawonga on the Murray River. The results confirm the positive response that can be expected from native fish to the reinstatement of large woody debris.
A secondary component of this program has been the establishment of a mark-recapture dataset that will provide estimates of the growth rates and population statistics of Murray cod, Trout cod and Golden perch. The dataset has already been used to assist the management of Murray cod. Another three years of data collection is necessary before the dataset will have the statistical power required to allow its inference to apply to other regions in the MDB (e.g. the utility of this data will have direct relevance to demonstration reaches in the area). The data will also provide the opportunity to confidently identify variation in the use of resnagged sites by different size classes of fish, which will provide the foundation for investment decisions with regard to resnagging in the region.
In 2006, 40 sites were sampled on the Murray River between Yarrawonga and Tocumwal to complete the mark-recapture data set to allow estimates of population statistics for Murray cod, Trout cod and Golden perch to be made. The Arthur Rylah Institute (ARI) also sampled the resnagging sites on the Murray River between Yarrawonga and Cobram to estimate the variance in use of resnagged sites by different size-classes of fish.
Results indicate that fish use logs restored to streams and sites can be optimised for particular species. The response is unequivocal for the critically endangered Trout cod, which underwent a biologically important increase in numbers following resnagging. For the other species the results are more variable, indicating that other habitat variables may also be necessary to increase the number of occupants of re-snagged rivers. These results demonstrate the importance of longer term monitoring to quantify restoration responses. They also highlight the value of testing restoration predictions before, or as part of restoration activities.
Hume to Yarrawonga: riparian and instream rehabilitation
In 2005–2006, The Living Murray project ‘Resnagging and Riparian Restoration – Hume Dam to Yarrawonga’ continued to make substantial progress, including:
- completion of the monitoring program to establish a baseline dataset of the distribution of large-bodied fish
- completion of a feasibility study for the implementation of the resnagging works at three high priority sites, including cost evaluation, works planning and detailed assessment of the effect of resnagging on geomorphology and flooding
- completion of a risk management plan and mitigation strategy to minimise the impact of the resnagging on other river users
- extensive landowner, agency consultation and Indigenous engagement
- development of an investment proposal and Commission approval of the proposal to implement the resnagging works at the three high priority sites.
A contract was developed between the MDBC and NSW Department of Natural Resources to implement Stage 1 of the project, at a cost of $1.184 million, to be completed by June 2007. A subsequent contract was established between NSW DNR and NSW Department of Primary Industries (Fisheries) to undertake these works, with NSW DPI (Fisheries) to employ a full-time project manager, implementation manager, work crew, and purchase required equipment and hire plant. By the end of June 2006, all existing stockpiles of timber were relocated to the riverbanks adjacent to Priority Site 2, downstream of Boiling Downs Creek.
During 2006–2007, implementation of the project will continue and include:
- an official launch of the project by Dr Wendy Craik Chief Executive MDBC in August 2006
- by September 2006, completion of resnagging at Priority Site 2, with placement of more than 200 snags, and commencement of resnagging at Priority Site 1, which will involve reinstatement of around 1,200 snags
- continuation of landowner consultation and communication of progress
- further sourcing of timber and relocation to Priority Site 1 for reinstatement during autumn and winter.
Presnagging fish community assessment at Paiwalla
An assessment of the fish community structure was conducted on 13–14 July 2006 by boat using electrofishing to collect baseline information prior to resnagging works near Paiwalla Wetland in the lower Murray, South Australia. Sampling was conducted at the Paiwalla resnagging site; an adjacent site with natural snags, and in upstream and downstream control reaches where habitat is similar to that at Paiwalla.
The sampling, undertaken by South Australian Research and Development Institute Aquatic Sciences, indicated that there was no significant difference in the structure of fish communities at the three sites for the seven species sampled (six native and one alien species). Those species were Unspecked hardyhead, Golden perch, Murray-Darling rainbowfish, Bony herring, Flathead gudgeon, Australian smelt and Carp.
The sampling identified that the resnagging design should consider the presence of two major habitat types within the resnagging reach. The research team suggested that snags be placed evenly into macrophyte and willow habitats within the resnagging reach to allow additional information to be gained during post-snagging assessment and further guide best practice resnagging in the lower Murray River of South Australia. Additional sampling prior to resnagging was also suggested to improve understanding of the fish community structure.
State and Territory highlights
In April 2006, the Queensland NFS Coordinator provided an update on the progress with demonstration reaches in Queensland to a workshop in Canberra. The workshop generated renewed enthusiasm for demonstration reaches and provided guidance for the progression of the concept for river rehabilitation across the Basin.
In a joint Queensland/New South Wales venture, a community-based project steering committee was established in September 2005 to progress the development of a demonstration reach on the Macintyre River in the Border Rivers Region. Aerial video mapping (AVM) along 1,178 km of the river is being used to complete a detailed riparian and aquatic habitat condition assessment of the demonstration reach, as well as being a tool to engage local communities in riparian management activities.
Planning for a demonstration reach on the Condamine River commenced. In 2006, funding was received to develop demonstration sites at Archer’s Crossing on the Condamine River and Bowenville Reserve on Oakey Creek at Bowenville. Activities to be undertaken include riparian replanting and fencing, resnagging and provision of fish passage.
In New South Wales, site plans were finalised for resnagging of the Hume Dam to Yarrawonga reach of the Murray River. Public liability issues were investigated, a Risk Management Plan was approved, and implementation of on-ground works commenced.
The installation of a de-stratification system at the ACT’s fire-affected Cotter Reservoir has proved effective in increasing dissolved oxygen levels in the water column, improving water quality and increasing habitat for Macquarie perch.
In South Australia, the community manages 27 wetlands. Sampling by the community has provided some interesting facts and new discoveries, including Dwarf flathead gudgeon at Swanport wetland, and has also provided the basis for restoration at some sites.
Photo: Dean Ansell
The effectiveness of the sand pumping operations at the Murray Mouth has been monitored by a combination of regular bathymetric surveys, aerial and satellite photographs and by monitoring the diurnal tide ratio (DTR) at Goolwa and Tauwitchere barrages. In 2005–2006 the works had achieved a clear improvement in water flow and connectivity between the ocean and the Coorong.
In Victoria, Regional River Health Strategies (RRHS) are being prepared for the State’s 10 Catchment Management Authorities. In 2005–2006 the northern RRHS were progressed. These strategies identify a number of high priority waterways within each region, based on consideration of reaches that are ‘of greatest value to the community’ and rivers that are ‘ecologically healthy’. Through the implementation of RRHS, and associated programs, the CMAs are undertaking numerous on-ground rehabilitation programs which have direct and indirect benefits to riparian and instream environments and thus native fish.
Two research projects were initiated in Victoria’s Wimmera region to improve understanding of distribution and status of fish and their habitat requirements at differing flows. The first, the Wimmera Fish Monitoring Program commenced in 2005–2006 and is designed to help assess the health of the catchment as well as to understand the impacts of specific events such as the release of environmental flows and the effect of sustained drought. The second program, completed in 2005–2006, involved the identification of specific habitat needs of native species at differing flows in waterways and the results will be utilised for habitat restoration projects throughout the Wimmera region.
The Murray Corridor Floodplain Rehabilitation Project, which commenced in 2000, is being undertaken on public land within a 300 km stretch of the Murray River floodplain between Hume Reservoir (upstream of Wodonga) and Barmah Forest (downstream of Tocumwal). Improvements to the flood regime for many of the wetland systems have already resulted, as was demonstrated during the provision of the 2005–2006 environmental water allocation to Barmah-Millewa—at least four wetlands flooded and connected to the river when they would not have done so without the earthworks having been undertaken.