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2015/16 Understanding the functional role of habitat structure to predation on Southern Pygmy Perch

  2015/16 Understanding the functional role of habitat structure to predation on Southern Pygmy Perch
Southern Pygmy Perch utilising artificial macrophyte habitat

Full Title

Structural habitat selection by Southern pygmy perch (Nannoperca australis)

Contact Person and

Funding Body

Murray Local Land Services (MLLS) with support from the Australian Government and its National Landcare Programme and in-kind contributions from MDFRC


2015 - 2016

Project objective

The present project were to determine whether:

  1. Southern pygmy perch preferentially select structured habitats over open ones and if so, to assess whether they show a preference for macrophyte habitats over woody habitats.
  2. Observed patterns of habitat selection vary when a predator (Redfin perch) is visible.
  3. The activity levels/metabolic rates of Southern pygmy perch differ when the fish are in structured versus open habitats.
  4. Observed patterns in activity levels/metabolic rate among habitats vary when a predator (Redfin perch) is visible.

The scientific knowledge delivered by this project will give managers an improved ability to: 

  • manage habitat in order to better support existing populations, and
  • identify suitable translocation sites based on structural habitat availability.


The Southern pygmy perch (Nannoperca australis) is a small-bodied fish species that historically was widely distributed throughout the Murray and lower Murrumbidgee systems. The species has experienced dramatic declines in range and abundance over the least twenty years and is now listed as endangered in NSW and South Australia. In NSW, there are only three known populations, two of which are located in the Murray Catchment near Holbrook and Albury. Currently, management of the two Murray populations is focused on maintaining the limited number of existing populations with a view to establishing new populations via translocations to suitable habitats in the future.

It is generally thought that aquatic plants (macrophytes) are a critical habitat feature for Southern pygmy perch. However, robust evidence for this is lacking and there is anecdotal evidence of self-sustaining Southern pygmy perch populations occurring in habitats with little or no macrophytes. It is not currently known whether Southern pygmy perch are associated specifically with macrophytes, or whether other structural habitat types, such as sticks, branches and logs, can fulfil the same functional requirements.


  • Southern pygmy perch demonstrated a statistically significant preference for structured habitats (macrophytes and wood) as compared to unstructured habitats.
  • Macrophyte habitat patches were selected by a significantly greater number of Southern pygmy perch than woody habitat patches.
  • Habitat selection was not influenced by the presence of Redfin perch.
  • Metabolic rates were significantly higher when macrophytes were present than when they were absent. This is indicative of higher rates of movement when the fish are in macrophyte habitats.
  • Metabolic rates were not influenced by the presence of Redfin perch.

The implications of this work for the management of existing Southern pygmy perch habitats and the selection of translocation sites:

  1. Management of existing Southern pygmy perch sites should focus on maintaining or creating significant areas of aquatic vegetation. Similarly, in the event that Southern pygmy perch are translocated to new sites, site selection should be strongly based on the presence of aquatic vegetation.
  2. Southern pygmy perch may be highly vulnerable to predators such as Redfin perch, which utilise aquatic vegetation as habitat. Consequently, management of existing Southern pygmy perch sites should aim to exclude predators that utilise macrophyte habitats, particularly introduced species, and translocation sites with these types of predators present should be avoided unless the predators can be eradicated prior to translocation.

Photo of the habitat preference tank setup with three habitat types: macrophytes, woody debris and open


PDFSouthern-Pygmy-Perch-Final-Report.pdf (811 KB)