The following is a short case study detailing the results of one such intervention monitoring project; ‘Food web study of zooplankton and fish, in relation to environmental watering in wetlands of the Lower Lakes’, undertaken by the University of Adelaide in 2009–10 (Wedderburn et al. 2010). This project was one of the first intervention monitoring studies which was shaped by the development of the ‘bundled hypotheses’ project. Specific hypotheses relating to food-webs which were developed by this process, and are answered through the study, include:
Flood-induced increases in diversity and abundance of zooplankton (emergence, immigration, reproduction) promotes recruitment in some fish species on the floodplain.
Shifts in zooplankton composition from small (rotifer-dominant) to large (microcrustacean-dominant) species are positively correlated with ontogenetic dietary shifts in fishes.
Floodplain recruitment in native fish species is impacted by alien fish species due to competition for prey items during developmental life stages.
Case study: assessing ecological benefits of environmental watering for threatened fish at the Lower Lakes
The MDBA provided funding to the South Australian Murray–Darling Basin Natural Resources Management Board towards research into the effects of using an environmental water allocation in the few remaining wetland habitats at the Lower Lakes. Dr Scotte Wedderburn, Dr Russell Shiel, A/ Professor Justin Brooks and Karl Hillyard from The University of Adelaide’s Water Research Centre sampled water quality, zooplankton and fish at Boggy Creek (watered site) and Mundoo Island (control sites) from November 2009 to March 2010.
Boggy Creek was sampled before and after environmental water allocations of several megalitres in early December 2009 and early February 2010. Murray hardyhead had begun breeding prior to the first watering, but zooplankton abundance was low and hence food supply was thought to limit growth and survivorship of the young fish over summer. Beneficially, the first watering event triggered a bloom in zooplankton (mostly the rotifer (Brachionus plicatilis) and its eggs (Figure )) that provided an abundance of food for young Murray hardyhead. Subsequently, the young developed strongly over summer, and by March 2010 the species had successfully recruited and the new adult population was secure.
The allocation of scarce environmental water should include targeting unique habitats in the Murray–Darling Basin and the threatened species they often hold. The maintenance of threatened fish populations in the few remaining wetland habitats at the Lower Lakes during the 2006-10 drought is paramount, so that these species re-establish in off-channel habitats when they re-fill. In understanding the ecological dynamics, successful management techniques for environmental watering can be applied.
Figure : Brachionus plicatilis with eggs (Left), Zooplankton sampling (Right).
17. APPENDIX G: DETAILS OF OTHER ECOLOGICAL MONITORING BEING UNDERTAKEN IN THE LLCMM ICON SITE.
Southern bell frog monitoring
As of 2011, The South Australia Murray–Darling Basin Natural Resources Management Board have undertaken two annual Southern bell frog censuses of Lakes Alexandrina and Albert. Previously managed by The Living Murray icon site team and funded through the State Drought Fund, the project is now managed and funded by DENR as a part of the Long Term Plan monitoring program. Refer to Figure for maps of known locations in 2009–10 and 2010–11. The location of southern bell frog hot-spots may be important in the future when prioritising key refuge sites for the delivery of environmental water.
The SA Murray–Darling Basin Natural Resources Management Board, in conjunction with the Goolwa to Wellington Local Action Planning group and Coorong–Tatiara Local Action Planning Association, have implemented a long-term (since 2003) community wetland monitoring program at several priority Lower Lakes wetlands. Photopoints, groundwater, surface water quality and level, fish, frogs and assistance with the lakes aquatic vegetation condition monitoring program are all undertaken. Priority wetlands include Narrung, Teringie, Waltowa, Loveday Bay, Dunns Lagoon, Hunters Creek/Boggy Creek system, Milang and Tolderol. The Living Murray program, through EWMP, has assisted with the management process for some of these priority wetlands by funding the development of several wetland management plans, and the design and installation of key flow control structures. In turn, the SA Murray–Darling Basin Natural Resources Management Board provide support to The Living Murray team by collecting valuable and frequent data on water quality and level, photopoints and frogs, at environmental watering sites in the Lower Lakes. As such, both programs are complimentary to the other, and have lead to more effective management of key Lower Lakes wetland sites.
Drought Action Plan threatened fish monitoring
The Protecting Critical Environmental Assets Program – Critical Fish Habitat and Refuge project is a recurring activity now in its fourth year of operation. Five species were identified as having undergone significant declines and thus a high priority for protection; Murray hardyhead (Craterocephalus fluviatilis), southern pygmy perch (Nannoperca australis), Yarra pygmy perch (Nannoperca obscura), river blackfish (Gadopsis marmoratus) and southern purple-spotted gudgeon (Mogurnda adspersa). This project covers 26 sites across the SA Murray–Darling Basin including 17 within the CLLMM Ramsar Boundary.
In response to extreme reductions in abundances and distribution of all of the five listed fish species, urgent action was undertaken in South Australia lead by the Department for Environment and Natural Resources (DENR) and included the support of a consortium of both Government and non-Government organisations collaborating to ensure the survival of these five targeted critically endangered freshwater native fish.
Figure : Southern Bell Frog distribution in the Lower Lakes in summer (a) 2009 and (b) 2010, based on call recognition, call playback and spotlighting
During 2007 a ‘Rescue to Recovery’ plan was implemented which targeted the conservation of these fish species and their habitats. Emergency intervention included; intensive monitoring, critical environmental watering, and as a last resort, rescue. Rescued fish were placed into a specialised captive breeding program as a back-up measure for wild stocks. The Drought Action Plan worked in alignment with The Living Murray Condition Monitoring program and intervention monitoring programs relating to threatened fish in the Lower Lakes, to assess the ecological response to types of interventions or environmental management actions at the CLLMM icon site. The Living Murray program also provided the foundation information for adopting an adaptive-management approach.
Recovery of these populations has been made possible by the success of specialised breeding programs and intensive monitoring coupled with an adaptive management approach. Juvenile river blackfish, Yarra pygmy perch, Murray hardyhead and southern purple-spotted gudgeon have been effectively reared in captivity with numerous juveniles being released into surrogate refuge sites which provide a stepping stone between captive breeding and wild reintroductions.
The surrogate site method was adopted when juvenile fish were successfully being produced through various captive breeding programs yet their wild habitats were still in critically poor condition.
Restoration of this species and other endangered native fish species is the long-term vision for the South Australian Murray–Darling Basin Natural Resources Management and Coorong Lower Lakes and Murray Mouth Long-term Plans and an adaptive management framework is being adopted to reach the best possible outcomes for reintroducing these important components of South Australia’s freshwater ecosystem.