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Controlling carp on the ’Bidgee

Published 21 Jun 2014 

Bret Peden and Mark Lintermans setting nets on the Murrumbidgee River.Bret Peden and Mark Lintermans setting nets on the Murrumbidgee River at Scotsdale. Photo by Perer Saunders

A major focus of the Upper Murrumbidgee Demonstration Reach (UMDR) - a 100 kilometre stretch of the Murrumbidgee River that runs past our Scottsdale Reserve in south‑east NSW - is learning more about controlling carp. An exciting new research project is fusing science with community engagement to track carp movements and trial control methods.

The common carp has a lot to answer for in Australia. Since its introduction around 150 years ago it has been implicated in the degradation of some of our greatest inland river systems.

The problem is carp are consummate opportunists. They can tolerate a broad range of conditions and habitats. With remarkable reproductive capabilities, few natural predators and a lifespan over 15 years, carp have become an international pest and one of the world's most invasive species.

The Murrumbidgee River, or ‘the ´Bidgee’ as it's affectionately known, supplies Canberra's water and supports a range of agriculture. On its journey downstream from the high‑country town of Bredbo, it winds along the north‑western edge of our Scottsdale Reserve.

Reserve Manager Peter Saunders with a native trout cod. Photo by Annette Ruzicka.Reserve Manager Peter Saunders with a native trout cod. Photo by Annette Ruzicka.

The Upper 'Bidgee provides critical habitat for three nationally threatened species (the Macquarie perch, Murray cod and trout cod) and three ACT‑listed threatened species (the Murray River crayfish, silver perch and two‑spined blackfish.

While these species were already in decline before carp arrived, the impact of carp has been devastating, with alien species now comprising up to 96 of every 100 fish caught.

Reducing carp numbers in the Upper 'Bidgee is difficult partly because of knowledge gaps. Not enough is known in the context of this upland riverine system about where carp live and breed, how they interact with other species, or how far they travel.

Reserve Manager Peter Saunders with a native trout cod. Photo by Annette Ruzicka.Photo by Peter Saunders

The UMDR's ambitious new research project aims to answer these questions – and more. Importantly, findings will also contribute to a growing pool of knowledge about the best way to tackle this environmental pest.

The project has three distinct parts. The first involves tracking carp with acoustic telemetry established by Prue McGuffie for a PhD project on Macquarie perch. The second part, to take place on Scottsdale Reserve, involves trapping and removing carp to ease pressure on a specific aquatic habitat and learn more about their population structure. The third part involves enlisting the local community to collect information about where carp are breeding and gathering.

Bush Heritage Healthy Landscape Manager, Peter Saunders, will lead the trapping trial at the northern end of Black Rock Gorge on Scottsdale. A four‑metre waterfall several kilometres upstream and a series of ‘riffles' and rapids downstream provide natural barriers that top and tail a pool called ‘the Basin'.

The good condition of this stretch of the river, and its relative remoteness, make it an excellent site for trapping. Peter and his team will ‘train' the Basin's carp to gather using thermal lures in winter and food lures in spring. The carp will be caught in nets, euthanised, studied and then used to fertilise a nearby organic farm.

Setting fyke nets on the Murrumbidgee. Photo by Annette Ruzicka.Setting fyke nets on the Murrumbidgee. Photo by Annette Ruzicka.

Meanwhile, local anglers will be asked to report carp sightings – including numbers, behaviour and size of fish using note books, an online portal or the soon‑to‑be‑released feralfiScan app. This will help create a more complete picture of carp presence and ‘hotspots' in the region.

Three community ‘carp outs' – sponsored fishing events with prizes for the most carp caught, largest and so on – will take place next January between Numeralla, Bredbo (near Scottsdale Reserve) and Canberra. With around 1,800 carp caught at a previous event, carp outs are a great way of engaging locals to support the project.

“Aquatically, our greatest challenge at Scottsdale is carp,” says Peter. “We hope this work will guide new trials for targeted carp removal to better protect our native  fish and habitats. The findings also have the potential to help protect native species on a much wider scale."

Scottsdale Reserve was acquired in 2006 with the help of David Rickards, in memory of Helen Rickards, the Vincent Fairfax Family Foundation and the Australian Government's National Reserve System program.