Supporting Document 4 from the NCCARF project ‘Adapting to climate change: a risk assessment and decision making framework for managing groundwater dependent ecosystems with declining water levels'.

Abstract

Freshwater fishes have been used as indicators of aquatic ecosystem health as many teleosts are sensitive to water quality and habitat decline. Developing field derived thresholds, or tolerance indicator values (TIVs), based on matching distributions with prevailing water quality and habitat variables is a common approach that allows modelling of population viabilities under changing environmental conditions such as declines in water quality or hydrology.  The freshwater fish fauna of south-western Australian is depauperate but has the highest rate of endemism of any Australian Drainage Division (82%).  It is highly imperilled due to existing anthropogenic stressors such as secondary salinisation and riparian degradation.  Secondary salinisation in particular has caused considerable inland range reductions of stenohaline species and the distributions of most are now limited to the western and southern parts of the region.  The importance of fresh groundwater in maintaining lentic and lotic refuge habitats during the naturally dry summer and autumn in the region has also recently been recognised.  For example, groundwater discharge during baseflow in the NCCARF project study area in the Blackwood River maintains habitat connectivity for the largest freshwater fish of the region, Tandanus bostocki and provides refuge habitat for the nationally endangered Nannatherina balstoni. However, modelling future population viabilities under projected surface and groundwater level reduction scenarios has been limited by the lack of TIVs for most species.  Therefore, the current study aimed to analyse an extensive database of fish distributions and water quality variables across south-western Australia (1098 sampling points) to develop TIVs for species that could then be used in a risk assessment and decision making framework for managing groundwater dependent ecosystems (GDEs) subjected to declining water levels in the Blackwood River.

There were significant differences between species in TIVs relating to water temperature and conductivity.  For example, some of the species that occupied narrow ranges and are considered to be threatened, such as Galaxiella munda and N. balstoni, occupied the coolest environments, whereas the common and widespread introduced Gambusia holbrooki and native Galaxias occidentalis occupied warmer and more saline environments.  The findings from the current supporting document were subsequently incorporated into the Bayesian Belief Networks (Supporting Document 6) that modelled the likelihood of population declines for species following groundwater level reductions in the Blackwood River during baseflow.  The BBNs were then mapped (Supporting Document 7) to spatially represent likelihood of population declines in the Blackwood River study area.  The TIVs developed here will also be extremely useful for modelling population declines in response to other projected environmental changes in south-western Australia, such as increasing temperature and salinity.

Please cite this report as:
Beatty, S, Morgan, D, Keleher, J, Lymbery, A, Close, P, Speldewinde, P, Storer, T & Kitsios, A 2013, Adapting to climate change: A risk assessment and decision making framework for managing groundwater dependent ecosystems with declining water levels. Supporting document 4: Environmental variables in the habitats of southwestern Australian freshwater fishes: An approach for setting threshold indicator value, National Climate Change Adaptation Research Facility, Gold Coast, 33 pp. 

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This photo is copyright Yarragadee intrusion zone of the Blackwood River, Western Australia © Stephen Beatty, Murdoch University, Freshwater Fish Group