Pillar 4 – Monitoring and Evaluation: Demonstration Reach Results

None of the existing demonstration reaches have been monitored for long enough for all the hypotheses to be fully tested, with no post-intervention monitoring undertaken for longer than 5 years. Nevertheless it is worthwhile presenting a brief summary of some of the results obtained so far to provide an indication of how variable ecological responses can be. The following information has largely been taken from a recent review by Boys et al. (2014). The reader is referred to this paper for more information.

Condition monitoring:

Several demonstration reaches have reported against reach scale condition targets, with varying results The Bourke to Brewarrina reach has been unable to detect any response by native fishes to the demonstration reach. Boys et al. (2014) suggest that this may be in part due to two factors; large inter-annual variability in fish abundance associated with floods in the Barwon-Darling River, and the relatively small scale of the interventions in relation to the large demonstration reach.

In contrast, preliminary analysis in the Ovens River demonstration reach suggests that Murray cod numbers may have increased since management interventions began. Macquarie perch numbers also appear to have increased in the Hollands Creek demonstration reach.

In the Dewfish demonstration reach the abundance of large bodied native fish, particularly Golden perch, have increased at two sites.

Intervention monitoring:

Intervention monitoring has been carried out at most reaches with variable results. Here the results from monitoring three particular interventions are discussed to illustrate some of the issues that may be encountered. Two of these management actions have been implemented widely within demonstration reaches and more broadly across river restoration in Australia. One (re-snagging) illustrates the results of directly monitored fish responses to the intervention while the second (riparian rehabilitation) discusses the use riparian condition as a surrogate. The third (alien fish management) is being implemented in a systematic way at two demonstration reaches only and the results are very preliminary.

Re-snagging (Large Woody Debris):

The most frequently implemented and evaluated management action in demonstration reaches has been re-snagging (five of the seven reaches). However, the impacts of this intervention on native fish populations have varied considerably.

In the Dewfish demonstration reach, preliminary data suggests that re-snagging has resulted in a significant increase in the numbers of Golden perch and Eel-tailed catfish, as well as a return of Murray cod individuals. Recent surveys (Norris, Hutchison and Chilcott, 2014) have confirmed that numbers of Golden perch, Murray cod, Eel-tailed catfish and Bony bream have remained much higher than before the reintroduction of large woody debris. In Oakey Creek in the Dewfish demonstration reach, few juveniles of large bodied species were captured after the 2013 summer spawning season suggesting that strong recruitment is not occurring in the area. The large woody debris may be acting as fish attractive devises only at this stage. There was no evidence that the numbers of small- bodied fish have increased due to re-snagging.

In contrast, monitoring of the impacts of re-snagging on fish populations in the Bourke to Brewarrina reach has failed to detect any significant effect on Golden perch or Murray cod numbers. Further to this, measurements of hydraulic and geomorphic indicators showed no response to the re-snagging either.

Although further monitoring is required to understand the reasons for the contrasting results for this management action, the differing results do highlight the need for monitoring even when the intervention is widely thought to be of benefit to native fishes and river health in general. It may also suggest the impact of re-snagging could be site specific and that the placement of snags may also be important.

Riparian rehabilitation:

Riparian restoration is widely practiced in Australia and the links between the riparian zone and fish habitat are well documented (provision of large woody debris, input of energy via leaf litter, shading, bank stability etc.). Riparian restoration is occurring in all demonstration reaches; however monitoring of its benefit to demonstration reaches is only occurring at the Upper Murrumbidgee and Dewfish reaches. Even here, monitoring of riparian related activities only relates to riparian condition, using this as a surrogate for fish condition. The focus has been on riparian health and not the impact that this may have on fish populations. However, some inferences have been made in the Dewfish demonstration reach, where extensive and better condition riparian vegetation has protected native grasses during drought and recent flood scouring. Fish assemblages at these sites have been more stable throughout variable climate conditions than at other sites with less healthy riparian vegetation.

Alien fish management:

Integrated Carp Management Plans have been developed for the Dewfish and Upper Murrumbidgee demonstration reaches. Both plans require a large number of coordinated actions to be taken to reduce Carp numbers. The Upper Murrumbidgee demonstration reach has only just started to implement the plan and at the moment on the focus is on gathering more knowledge. The Dewfish demonstration reach has been removing Carp from sections of the reach but has yet to implement all of the components of the management plan. However, Carp numbers have been kept at a low level at a number of sites. Monitoring of the impact of interventions to control Carp is complex as there will be a large number of activities that will be required in order to have a significant impact. It is most likely that combined impacts will be noticed during condition monitoring rather than intervention monitoring.