By Ben Broadhurst
Cover image – Ben Broadhurst (left) and Rhian Clear (right) pulling fyke nets during a fish survey on the Cotter River (Photograph Lynda Coulson see http://lyndacoulson.com.au/).
Magic moments, the stuff we work for. I’ve been lucky enough to share a few over the journey so far. This magic moment occurred on a November day back in 2006. Myself and Rhian Clear (Frysie) had been conducting snorkelling surveys of the Cotter River to the west of Canberra looking for larvae and juvenile Macquarie perch. So far we had recorded a number of these in the first few pools immediately upstream of the Cotter Reservoir, which is a known strong hold of this endangered species. The pools immediately upstream of the reservoir were thought to be be important spawning locations by the presence of early juveniles observed snorkelling by Brendan Ebner & his team in 2001/2002. That year a fishway was installed some 6km upstream of the reservoir to provide Macquarie perch access to a further20-odd kilometres of stream in the hope that they would surmount the previously impassable road crossing and establish in the river upstream. Initial surveys failed to detect the presence of Macquarie perch above the fishway, despite all measurements and design characteristics suggesting that the fishway would be passable. Some years went by until a few observations of Macquarie perch upstream of the fishway started to trickle in, mostly by anglers, but one by a researcher in Brendan’s new team, a bloke who puts the “i” in team, literally (Jason Thiem). Spurred on by this, Brendan and myself set about designing a robust snorkelling technique to survey the river from the reservoir to a few kilometres upstream of the fishway to determine if indeed Macquarie perch had used the fishway to gain access to the river upstream to breed. Anyway, I digress (I’ve noticed a few of us on the Lair have digressive tendencies), on a nice November afternoon myself and Rhian were in the 3rd last pool of the day, when I noticed a very small larval fish. I promptly scooped up the little fish and placed it in a jar of river water. It didn’t have a forked tail, so that ruled out any of the likely exotics, leaving only Macquarie perch and Two-spined blackfish (common throughout the river). Somewhat buoyed by the prospect of discovering larval Macquarie perch several kilometres upstream of the fishway, we retained the specimen for further examination back at the lab (which was ultimately inconclusive).
Our next fortnightly snorkelling trip couldn’t come soon enough. In the second pool upstream of the fish way (some 1.5 km upstream), we hit the jackpot. Not one miserly little indiscriminate larval fish, but hordes of early juvenile Macquarie perch! There they were, buzzing about, predating upon microinverts, darting to and from cover in and out of the flow in the headwaters of each pool. In some pools, large schools of larvae hung in the water column hugging steep rock faces, moving deeper upon approach. They had done it! These placid, patient, beautiful native fish had pushed though the fishway, well up river and got their jiggy on! I’m pretty sure I even got a high-five out of Frysie that day, one of very few ever given as he is not keen on unnecessary physical contact. That day we recorded larvae or early juvenile Macquarie perch in 11 of the 13 pools we snorkelled upstream of the fishway (spanning 3.5 km). Certainly a research highlight, one that I’ll never forget!
Ben Broadhurst (foreground) and Rhian Clear (background) conducting a snorkelling survey for larval and juvenile Macquarie perch in the Cotter River (Photograph: Mark Jekabsons).
Since that day, regular sampling by fyke nets and backpack electro-fishing have detected several age classes of Macquarie perch present in the river upstream of the fishway indicating that this population had colonised this newly accessible part of the range that had been taken from them. This success has also resulted in the fishway being repaired by flood damage on two occasions and another fishway being built further up the catchment.
Broadhurst B., Ebner B., Clear R. (2012) A rock-ramp fishway expands nursery grounds of the endangered Macquarie perch Macquaria australasica. Australian Journal of Zoology 60: 91–100.
Broadhurst B.T., Ebner B.C., Lintermans M., Thiem J.D., Clear R.C. (2013) Jailbreak: A fishway releases the endangered Macquarie perch from confinement below an anthropogenic barrier. Marine and Freshwater Research 64: 900–908.
Ebner, B., and Lintermans, M. (2007). Fish passage, movement requirements and habitat use for Macquarie perch. Final report to the Department of Agriculture, Fisheries and Forestry Australia. Parks, Conservation and Lands, Canberra.