A new population of one of the Murray-Darling Basin’s endangered fish has recently been discovered in the lower Lachlan.
Olive perchlet – a small, transparent and carnivorous fish – is listed as an endangered species in western New South Wales. Until recently, only a single population was known from the Lachlan River in the weirpool that diverts water into Lake Brewster.
Fish ecologist, Landcare co-ordinator and Lake Cargelligo resident Dr Adam Kerezsy works from the headwaters of the Lachlan all the way down to the Great Cumbung Swamp near Oxley and says he’s been keeping an eye out for perchlet for more than 10 years.
‘I certainly wasn’t expecting them down in the Booligal area to be honest, but the nets don’t lie, and sure enough, on a cold morning in April there they were – and in good numbers.’
Olive perchlet get to about 5 – 6cm in length, and are a floodplain specialist, meaning they’re more likely to boom in numbers and colonise new habitats during periods of elevated flow.
‘It’s likely that they’re members of the Brewster population that have moved, bred and prospered during the big floods of 2022. Alternatively, they may be a separate population that has been there all along, but that we just haven’t found because the Lachlan’s a big river, and it’s taken us until the 2020s to start surveying the more remote off-channel areas. We’ll analyse their DNA and that may help sort out the mystery’.
Kerezsy insists that the discovery is a joint effort and that without the co-operation of a large number of organisations the work simply wouldn’t occur.
‘The surveys in April were supported by the University of Canberra and the Commonwealth Environmental Water Office. Then I went back in May and this was supported by NSW Department of Planning and Environment. All the way along landholders are obviously vital to the processes of surveying and accessing these areas. Once we decide on management options it’s certain that NSW Fisheries will play a role. This is the only way we can slowly-but-surely keep chipping away at improving the health of our rivers and the critters that we want to maintain. We all have to work together’.
For now, it’s a fantastic outcome for the lower Lachlan River. Despite river regulation and carp, there are still isolated patches of habitat that can sustain populations of endangered species.
‘One of my “bosses” from one of the agencies used to say to me, half-jokingly, “find me some perchlet!”. Well it’s taken about 15 years but it’s finally happened. The next challenge is looking after them.’
Contributed by Adam Kerezsy.