Posted by Siwan Lovett | March 23, 2016
A Blakney Creek landholder has combined forces with Fisheries NSW, South East Local Land Services and Rivers of Carbon to construct two in-stream barriers to prevent the spread of alien fish and protect one of the last populations of the rare and endangered Southern Pygmy Perch in NSW.
Southern Pygmy Perch are a small native fish and are in real trouble, with only three small isolated populations remaining in NSW, and only one in the Lachlan catchment. The threat of this species becoming extinct in NSW is very high. One of the major causes for the decline in Southern Pygmy Perch is competition and predation from alien species, particularly European Carp and Redfin.
A recent invasion of Redfin into Blakney Creek has been decimating the population of Southern Pygmy Perch within that system. The Redfin have been moving up stream progressively, wiping out the Pygmy Perch as they go. With no real means of eliminating the Redfin at this stage, a project was undertaken to identify areas within the system that Redfin had not reached, and then try to stop them invading these areas.
Techniques including environmental DNA sampling, electrofishing and netting were employed to determine the extent of the Redfin invasion and to identify any areas that they had not yet reached. Of all the areas investigated, only one small section of the upper Urumwalla Creek was identified that contained good numbers of Southern Pygmy Perch, suitable habitat and no Redfin.
With funding and resources from the South East LLS and the Rivers of Carbon partnership of Greening Australia and the Australian River Restoration Centre, over 175 tons of large rock was used to construct two in-stream barriers to prevent the upstream movement of alien fish to protect the Southern Pygmy Perch that reside in the upper reaches of the creek. The rock walls were designed and constructed by South East LLS staff who specialise in these types of works.
The site where the barriers were constructed also had a pre-existing erosion head cut. The construction of the structures will not only benefit the Pygmy Perch above them, by protecting them from predation by Redfin, but will also protect their habitat from being undermined by erosion. The stabilisation of this erosion is expected to benefit the health of the system downstream by reducing sediment input and improving water quality.
While the population of Pygmy Perch above this barrier are safe for now from alien fish, a broader project is currently running with Gunning Landcare group to try to identify locations safe from alien fish where other populations of Southern Pygmy Perch can be established.
Story by Luke Pearce, Fisheries New South Wales
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