Ecological Communities - A Biological Survey of the Murray Mouth Reserves

• Summary
• Full Report

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Summary

The Field Survey

Reedbeds and the Coorong lagoon (Photo: Tony Robinson)

Male and female Southern Pygmy Perch a locally endangered fish (Photo: Mike Hammer)

Swamp Rats were common in dense sedge lands around the lakes (Photo: Steve Doyle)

Eastern Tiger Snakes showed a variety of colour forms in the area (Photo: Peter Canty)

The Murray Mouth Reserves incorporate the range of habitats that remain in a natural and semi-natural state at the terminus of the Murray River and the tidal inlet for the Coorong. Three National Parks and Wildlife managed reserves cover approximately half of this area including all of the Coorong and Younghusband Peninsula, a fifth of Hindmarsh Island and a group of smaller islands surrounded by freshwater as Mud Islands Game Reserve. The waters of the area are separated between fresh and saline by a series of barrages built in the 1930s to hold fresh water in Lakes Alexandrina and Albert. The terrestrial habitats of the area are primarily a coastal barrier dune that is breached by the outlet to the Murray River but now mostly acts as a tidal inlet for the saline waters of the Coorong and Goolwa Channels. The coastal scrub that dominates these dunes is largely intact having only been slightly modified by stock grazing in most areas. The remaining habitats occur on a number of low islands of which Hindmarsh Island is the biggest. Natural habitat on the islands has been substantially lost or altered for grazing and cropping. Only small areas of saline and wetland habitats remain in natural form. Significant reedland habitat has naturally established on the more reliable freshwater wetlands and island margins following the damming of the Lakes with the barrages.

The Biological Survey of the Murray Mouth Reserves aimed to describe the remaining habitats in the area, to document the flora and fauna, and to map the remnant native vegetation communities of islands of the Murray Mouth at 1: 50,000 scale. Methods used to sample the vascular plants, mammals, birds, reptiles and amphibians followed the standard techniques for the Biological Survey of South Australia. The survey incorporated plant data from 53 existing survey sites dating back to 1982, of which twelve also had fauna information. The current survey added plant and fauna information from a further 22 sites.

Survey Results

Two hundred and seventeen plant species were detected at survey sites of which 34% were non-indigenous. The vegetation communities of the area were grouped into eleven associations using cluster analysis based on presence/absence of species at each site (annual species were removed from the analyses). No plants with national or state conservation ratings were recorded at sites. Forty-six species with a regional rating in the Southern Lofty region were recorded at survey sites.

Twelve species of mammals of which four are native to the area were recorded at survey sites and a further three native species were observed opportunistically within the study area. No species with national or state conservation ratings were recorded.

Fifteen reptile and two frog species were recorded at survey sites. No species with conservation significance were recorded though the capture of a Red-bellied Black Snake on the south-eastern end of Hindmarsh Island extended the known distribution of this species. Tiger Snakes were also of interest with both the Eastern Tiger Snake and the Black Tiger Snake co-existing and possibly hybridizing in this area.

Eighty-five bird species were recorded at 22 sites (9% were waders and 27% were waterbirds). The four nationally threatened species that are known to live or occasionally visit the study area were not recorded during the survey. Twenty-one species are considered vulnerable under South Australian legislation. The area provides significant breeding habitat for two of these (Rufous Bristlebird and Lewin's Rail). The area also supports 21 species rated as Rare in South Australia and provides an important breeding area for four of these (Musk Duck, Baillon's Crake, Southern Emu Wren and Golden Headed Cisticola).

This survey differed from most terrestrial surveys by having a significant freshwater fish and aquatic invertebrate component. The freshwater fish survey detected a surprising diversity of species (19 species from ten sites sampled). Of these 16 were native and four were introduced. Two species are considered Nationally Vulnerable (Yarra Pygmy Perch and Small-mouth Hardyhead). The other two have South Australian conservation ratings (Southern Pygmy Perch [Endangered] and Dwarf Flathead Gudgeon [Rare]). The numerous smaller channels characteristic of the Wyndgate Reserve on Hindmarsh Island provide a diversity of habitats with healthy macrophyte communities that may be critical for the survival of these small threatened fish species in this area of the Murray River.

The reserves and private lands of the Murray Mouth region represent a contrast of relatively intact coastal marine habitats along the major peninsulas and the largely cleared or degraded habitats of the islands. The area appears to be most important for the conservation of aquatic birds and fish: the altered estuarine Coorong system for aquatic birds, and the artificial freshwater system of Lake Alexandrina for fish. Each of the habitat types appears to be important for at least one species of conservation significance, even the cropping land, which provides important grazing areas for the large non-breeding population of Cape Barren Geese. Further work targeting frogs and fish across more of the island habitats is required to get a better understanding of the significance of the wetland communities within the recently purchased Wyndgate Reserve on Hindmarsh Island.

Vegetation Mapping

Vegetation had been mapped across the survey area at a variety of scales. The survey relied on visual interpretation of 1:20,000 aerial photographs together with the existing mapping to produce a new vegetation map at a scale of 1:40,000. A total of 10 vegetation communities were mapped.

These vegetation maps are part of an ongoing program to ultimately produce vegetation maps at three regional scales to cover the whole State.

Reference: Brandle, R. (ed) (2002). A Biological Survey of the Murray Mouth Reserves, South Australia, March 2002. Biodiversity Survey and Monitoring Program, National Parks and Wildlife South Australia, Department for Environment and Heritage, South Australia.

Full Report

A full report of 'A Biological Survey of the Murray Mouth Reserves, South Australia' (5.2Mb PDF file) is available an Acrobat PDF file.

Please note that the above file large and may take a while to download and to search this file you will need to open the "Bookmarks tag" within it. If you have any problems please contact Robert Brandle or phone (61 8) 8222 9471.