Darling River Snail Indicative Distribution in NSW

The Darling River Snail (also known as ‘River Snail’) is a mediumsized (20-25 mm) freshwater snail that was once common and\r\nwidespread in the Darling River and its tributaries. However\r\npopulations declined rapidly over the last few decades, probably as a\r\nresult of weir building and other activities associated with river flow\r\nmanagement. They are now virtually extinct throughout their natural\r\nrange. In the last decade, living specimens have only been found\r\nfrom within irrigation pipelines in southern NSW. They are a critically\r\nendangered species – www.dpi.nsw.gov.au/fishing/threatenedspecies/threatened-species-list/critically/river-snail/river-snail\r\nThe methods used to create the predicted current distribution of the\r\nDarling River Snail are described fully in: NSW Department of\r\nPrimary Industries (2015), NSW Fish Community Status 2015 – Final\r\nReport.\r\n\r\nAll available records of the species were collated and assessed for\r\naccuracy. For current distribution, only records after 1 January 1994\r\nwere used. Within the framework of the Australian Hydrological\r\nGeospatial Fabric V2 surface hydrology network, the records were\r\nassociated with attributes from the National Environmental Stream\r\nAttributes Database and River Styles® geomorphology. The\r\nAustralian Hydrological Geospatial Fabric V2 surface hydrology\r\nnetwork (Geofabric) is a fully connected and directed stream network\r\nbased a 9 second DEM. It allocates a unique stream segment\r\nnumber to each river reach in Australia. The Environmental\r\nAttributes Database is a set of lookup tables supplying attributes describing the natural and anthropogenic characteristics of the\r\nstream and catchment environment that was developed by the\r\nAustralian National University (ANU) in 2011 and updated in 2012.\r\nThe data is supplied as part of the supplementary Geofabric\r\nproducts which is associated with the 9 second DEM derived\r\nstreams and the National Catchment Boundaries based on 250k\r\nscale stream network. 30 Stream variables were assessed for the\r\nmodelling.\r\nRiver Styles® provides a high resolution categorical classification of\r\nriver character within a nested hierarchy of criteria based on valley\r\nsetting, channel planform, geomorphic units, and bed material. The\r\nNSW Office of Water compiled a spatial dataset of River Styles®\r\nclassifications for a large number of the waterways of NSW. From 65\r\nRiver Style® categories we generated two new fields representing\r\nPlanform (34 categories) and Substratum (8 categories) for each\r\nstream segment. River Style® planform and substratum categories\r\nwere then assigned to each Geofabric segment.\r\n\r\nMaxEnt 3.3.3 is a widely used species distribution modelling program\r\nthat utilises presence records to generate probabilities of occurrence\r\nbased on a suite of environmental variables quantified across the\r\narea of interest. It was used to model the current geographic\r\ndistribution of each listed threatened freshwater aquatic species or\r\npopulation. We utilised logistic output to plot the predicted\r\ndistribution of each species. This output equates to a probability that\r\nthe species will be observed in each river reach, given the\r\nenvironmental conditions that exist there relative to the\r\nenvironmental conditions where the species is known to occur. For\r\nthis mapping, above 33% probability was considered predicted\r\npresence. Only stream segments with a modelled average daily flow\r\nof more than five megalitres were selected for output. In addition,\r\npredicted separate populations were connected by manual\r\ninterpretation. The predicted values for each river reach were\r\nconverted from the Geofabric framework to the higher resolution\r\n2013 NSW Strahler Stream Order Hydroline.