Aquatic Fauna Survey of Wetlands 351 and 491 near Wentworth, South-West NSW, November 2004

"2005".

Project Number: Aquatic fauna survey of two NSW wetlands - M/BUS/75.

MDFRC item.

The NSW Murray Wetlands Working Group Inc. are investigating options for implementation of on ground works such as regulators to restore more natural hydrological regimes to Wetlands 351 and 491 (River Murray Database) in the Lower Murray-Darling Region. This survey aims to gauge the ecological condition of the wetlands, collect baseline data on the diversity and abundance of aquatic fauna in each wetland, and provide recommendations for future management and monitoring of the wetlands to increase the biodiversity of the wetlands. A baseline survey of water quality and aquatic fauna was conducted at four sites within Wetland 351 on 3-4 November 2004 and four sites in Wetland 491 on 8-9 November 2004 (electro-fishing of both wetlands was conducted on 8 November 2004). Both Wetlands 351 and 491 contain diverse fish and macro-invertebrate communities, comparable in species richness to other similarly regulated wetlands in the Lower Murray-Darling and Mallee regions. The water quality in Wetlands 351 and 491 did not differ considerably to that of other wetlands recently surveyed in the Lower Murray-Darling and Mallee regions. Significant differences in water quality parameters between the two wetlands were identified for pH and electrical conductivity. The difference in salinity is caused predominantly by a groundwater intrusion between Wetland 351 and the Murray River, thus elevating the electrical conductivity in the wetland. In both wetlands electrical conductivity increased with distance from the inlet channel due to regular inflow of less saline water at the inlet end of each wetland. Wetland 351 recorded higher concentrations of total nitrogen and phosphorus then Wetland 491, possibly a result of agricultural runoff from irrigated crops adjacent to Wetland 351. There were no significant differences between the biologically available forms of either nitrogen (NOx) or phosphorus (FRP). All of the native and introduced fish species sampled in this survey are considered to be common and widespread within the Lower Murray-Darling River system. No significant differences in fish abundance or species diversity between Wetlands 351 and 491 were detected (all P values > 0.05). Carp gudgeon complex and Flyspecked hardyhead were the most abundant native species in both wetlands, while Gambusia was the most abundant introduced species. Eight native fish species were recorded in Wetland 351, while only 5 were recorded in Wetland 491, with Golden perch, Flat head gudgeon and Dwarf-flathead gudgeon absent from Wetland 491. Yabbies, Eastern long-necked turtles and the Victorian FFG listed Broad-shelled turtle (Department of Sustainability and Environment 2004) were recorded in both Wetlands 351 and 491, while the Murray turtle was only recorded in Wetland 351. A greater number of macro-invertebrates were collected from Wetland 351 (1,099 individuals) then Wetland 491 (286 individuals), although Wetland 491 recorded higher abundances of macro-invertebrates from less environmentally tolerant taxa. Ten taxa were recorded in each wetland with five taxa common to both wetlands. A greater abundance of the taxa Notonectidae (Backswimmers) in Wetland 351 was largely responsible for the difference in total macro-invertebrate abundance between the two wetlands. In both Wetlands 351 and 491 taxa richness was greater at sites closest to the inlet channel and which contained more macrophytes. The absence or low abundances of several fish species and macro-invertebrate taxa (such Golden perch, Bony bream, Crimson-spotted rainbowfish, Mayfly larvae and Caddis fly larvae) suggest the health of neither wetland is good, and is most likely a consequence of both wetlands permanent inundation. Key Recommendations: - By re-instating a more natural hydrological regime that incorporates a dry phase, the productivity of Wetlands 351 and 491 would be predicted to increase in the short to medium term, with an expected shift in aquatic communities from those associated with more permanent systems to communities more closely associated to the natural ephemeral nature of both wetlands. - Should such a dry phase be imposed, an a priori assessment of risk to both the wetlands and to short-term riverine salt concentrations, (including regular monitoring of the level and salinity of local groundwater), would be required to adequately assess potential impacts of evapo-concentration of salts and rising saline ground water. - Decisions regarding the timing of wet-dry phases and the form of regulator installed to facilitate drying/wetting events will depend on the biota specific ecological objectives and management objectives of the imposed water regime change. - Should a dry phase be reinstated to Wetlands 351 and 491, it is suggested that uncontrolled access by stock and feral animals should be restricted, where possible, to protect and minimise their impact on water quality. - Regular (ideally seasonal or more frequent) monitoring of water quality, groundwater, macro-invertebrate and fish communities would enable managers to assess the success and impacts of future alterations in the hydrological regime of either wetland. Methods of data collection and identification in any future monitoring program should be consistent to those used in this study. This will provide early 'before' data against which future water quality, aquatic macro-invertebrate and fish data can be compared.