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
widespread in the Darling River and its tributaries. However
populations declined rapidly over the last few decades, probably as a
result of weir building and other activities associated with river flow
management. They are now virtually extinct throughout their natural
range. In the last decade, living specimens have only been found
from within irrigation pipelines in southern NSW. They are a critically
endangered species – www.dpi.nsw.gov.au/fishing/threatenedspecies/threatened-species-list/critically/river-snail/river-snail
The methods used to create the predicted current distribution of the
Darling River Snail are described fully in: NSW Department of
Primary Industries (2015), NSW Fish Community Status 2015 – Final
Report.

All available records of the species were collated and assessed for
accuracy. For current distribution, only records after 1 January 1994
were used. Within the framework of the Australian Hydrological
Geospatial Fabric V2 surface hydrology network, the records were
associated with attributes from the National Environmental Stream
Attributes Database and River Styles® geomorphology. The
Australian Hydrological Geospatial Fabric V2 surface hydrology
network (Geofabric) is a fully connected and directed stream network
based a 9 second DEM. It allocates a unique stream segment
number to each river reach in Australia. The Environmental
Attributes Database is a set of lookup tables supplying attributes describing the natural and anthropogenic characteristics of the
stream and catchment environment that was developed by the
Australian National University (ANU) in 2011 and updated in 2012.
The data is supplied as part of the supplementary Geofabric
products which is associated with the 9 second DEM derived
streams and the National Catchment Boundaries based on 250k
scale stream network. 30 Stream variables were assessed for the
modelling.
River Styles® provides a high resolution categorical classification of
river character within a nested hierarchy of criteria based on valley
setting, channel planform, geomorphic units, and bed material. The
NSW Office of Water compiled a spatial dataset of River Styles®
classifications for a large number of the waterways of NSW. From 65
River Style® categories we generated two new fields representing
Planform (34 categories) and Substratum (8 categories) for each
stream segment. River Style® planform and substratum categories
were then assigned to each Geofabric segment.

MaxEnt 3.3.3 is a widely used species distribution modelling program
that utilises presence records to generate probabilities of occurrence
based on a suite of environmental variables quantified across the
area of interest. It was used to model the current geographic
distribution of each listed threatened freshwater aquatic species or
population. We utilised logistic output to plot the predicted
distribution of each species. This output equates to a probability that
the species will be observed in each river reach, given the
environmental conditions that exist there relative to the
environmental conditions where the species is known to occur. For
this mapping, above 33% probability was considered predicted
presence. Only stream segments with a modelled average daily flow
of more than five megalitres were selected for output. In addition,
predicted separate populations were connected by manual
interpretation. The predicted values for each river reach were
converted from the Geofabric framework to the higher resolution
2013 NSW Strahler Stream Order Hydroline.

Tags: Ecology, FISHERIES, Freshwater, Habitat, Threatened species
Organization: Department of Primary Industries and Regional Development (DPIRD)