Category Archives: Pest animal issues & solutions

Evaluation of carp exclusion screens at wetland inlets

Key words: pest fish control, European Carp, exclusion screen, Native Fish Strategy

Threats and Impacts: Wetlands are sites of high primary and secondary production and contain diverse flora and fauna. Indeed, many riverine species are wholly or partially dependent on wetlands for food, shelter or habitat during some part of their life cycle. Carp (Cyprinus carpio) dominate the alien fish fauna of the Murray–Darling Basin, and are believed to impact on native fish communities by increasing turbidity, disturbing and redistributing benthic seeds and invertebrates, up-rooting delicate shallow-rooted vegetation, competing with native fishes and other aquatic fauna for food and space, and indirectly promoting the development of toxic algal blooms (Fig 1).

In the Murray-Darling Basin, up to 98% of Carp are produced in wetlands connected to the main rivers. Carp Exclusion Screens (CES), which are mesh barriers that are installed at inlets to wetlands to exclude large fish from enterin (Figs 2-3), provide a management tool that has been applied to protect ecologically important areas from the impacts of Carp. However, little work has been undertaken to validate the effectiveness of CES in managing Carp, and concerns about possible detrimental effects of CES on native aquatic fauna have been raised.  

Broad aim and specific objectives: The project had three broad aims:

  1. evaluate the effectiveness of CES at wetland inlets;
  2. assess possible impacts of existing screen configurations on native fish communities that would normally access wetlands; and,
  3. design (if possible) an optimised CES to allow small and medium sized native fish to pass in and out of wetlands whilst denying access to mature carp.

Methods: The aims of this project were achieved by undertaking six key research activities:

  1. a desktop literature review and a field reconnaissance to evaluate the existing diversity in the design and management of CES within the Murray–Darling Basin;
  2. analysis of available data from recent comprehensive wetlands surveys (the 2004–2007 South Australian River Murray Wetlands Baseline Surveys) to evaluate differences in the relative abundances of carp and native fishes in wetlands with and without CES;
  3. identification of the species composition and sizes of fishes and other aquatic fauna that make lateral migrations through wetland inlets and which might, therefore, be affected by the use of CES;
  4. modelling to establish the size range of large-bodied fish that could pass through different screen mesh dimensions;
  5. calculation of ‘optimised’ mesh designs that would prevent the passage of mature, breeding-size carp (>250 mm TL) whilst allowing the passage of a majority of small and medium sized native fishes that use wetlands; and,
  6. laboratory and field trials of the most common existing screen mesh designs versus the optimised designs.
Figure 1: Carp accumulating downstream of a Carp exclusion screen at Sweeneys wetland. (Photo courtesy SARDI)

Figure 1: Carp accumulating downstream of a Carp exclusion screen at Sweeneys wetland. (Photo courtesy SARDI)

Figure 2: Carp Screens installed on a channel at Riverglades SA.  (Photo courtesy Leigh Thwaites)

Figure 2: Carp Screens installed on a channel at Riverglades SA. (Photo courtesy Leigh Thwaites)

Figure 3: Pivoting carp screen adjustment at Ramco SA. (Photo courtesy of Leigh Thwaites

Figure 3: Pivoting carp screen adjustment at Ramco SA. (Photo courtesy of Leigh Thwaites

Findings: The current CES designs and management regimes were noted to have been ineffective in reducing the numbers and biomass of Carp in wetlands.

A diverse and abundant native fish community (14 species) was found to utilise wetlands and wetland inlets. Some existing exclusion screen designs are detrimental to native fish (by excluding most sizes and life history stages), including species of conservation significance. Other aquatic fauna, such as turtles, are also likely to be impacted.

Two types of screens that will optimise the exclusion of large, sexually mature carp were designed:

  • A square grid mesh with 44 mm gaps
  • A “jail-bar” design with 31.4 mm gaps.

The jail bar design was found to collect less debris, trap more Carp and less native fish, and had little effect on flow velocity.

Lessons learned and future directions:CES may be beneficial as part of an integrated Carp management regime in some wetlands. Presently, there is no benefit in using CES in permanently inundated wetlands, unless other Carp reduction measures are also employed.

  • The use of CES alone should be considered for use at seasonal/ ephemeral wetlands that dry every 1-2 years. They may also be suited to permanent shallow wetlands that remain filled for >2 years at a time, if it can be shown that all adult Carp migrate from wetlands to overwinter in deeper river water.
  • The jail bar CES with 31 mm apertures between bars screen passed more native fish, including the greatest proportion of Bony Herring (Nematalosa erebi) (>90%), which are the key large-bodied native fish found to use wetlands and wetland inlets.
  • All CES need to be regularly maintained to ensure that they are functioning as intended and are not altering channel hydrodynamics or impeding the passage of native fauna.

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy.

Contacts: Dr Leigh Thwaites, South Australian Research and Development Institute. Tel: + 61 8 8207 5495, Email:

Link: Not yet published.

Carp Separation Cages

Key words: Introduced fish, Pest fish, Carp, Carp Cage, Native Fish Strategy

Fishways facilitate movement of both native and non-native fish and thus provide species such as carp with a significant opportunity to migrate and disperse upstream. Common Carp (Cyprinus carpio, henceforth referred to as Carp) are highly migratory and often dominate the biomass utilising fishways. A carp separation cage (CSC) is a specially designed trap, usually installed on infrastructure such as a fishway, that takes advantage of the jumping behaviour of migrating Carp by drafting them into a holding cage for later removal, while allowing native fish to continue swimming upstream.

Broad aim: The aim of this project was to develop low cost technology to automatically separate adult carp from native fish, and to identify the season, time(s) of day, environmental cues and biomass of adult and juvenile Carp migrating in fishways to better target the use of the technology.

Methods: Two versions of the CSC were trialled within a straight section of a channel near a fishway at Torrumbarry Weir on the middle reaches of the Murray River about 1630 km from the Murray mouth. A design was first trialled requiring manual operation, with on-site weir keepers checking for fish every 24 h. Fish were removed daily. A second automated design was later trialed incorporating a mechanical counterweight system to automatically crowd and release non-jumping fish via a lifting false floor and native fish exit gate. A cage was placed at the exit of the fishway to trap, count, and measure all fish that exited the crowding system.

Carp being harvested from a Carp cage. (Photo by Ivor Stuart)

Figure 1. Carp being harvested from a Carp cage. (Photo by Ivor Stuart)

Findings: The prototype CSC demonstrated that large numbers of Carp can be removed with minimal catch of native fish. However, the need to manually release any trapped native fish limited the application of the technology, especially in remote areas. Subsequent versions of the initial design resulted in several improvements, including:

  • being able to operate on the exit of any fishway type (Denil, vertical-slot, lock);
  • an increase in the biomass of Carp and native fish that can be held;
  • trapped fish can be held in lower water velocity conditions;
  • native fish are exited into the weir pool rather than into the fishway;
  • the cage is now more transferable among exits or different fishways; and
  • access and removal of Carp is more efficient.

Lessons learned and future directions: This study highlighted the opportunity to utilise fishways to remove Carp. The CSC should be targeted to periods of strong carp movement. Spring is a critical time for native fish movement and utilising the technology outside the spring period will maximise catches of Carp but minimise disruption to native fish movements.

For both monitoring and Carp removal purposes it is essential that trap construction, fishway trapping and data collection are standardised across the many locks and weirs of the Murray River.

A commercial trial of the CSC in the fishway at Lock 1 (Blanchetown) has been underway for some years.  From 2007-2011, 300 tonnes of Carp have been harvested.

The CSC has also been modified to suit Carp separation at wetlands.

Carp cage installed at Turrumbarry. (Photo by Ivor Stuart)

Figure 2. Carp cage installed at Turrumbarry. (Photo by Ivor Stuart)

Stakeholders and Funding bodies: This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy and undertaken by Ivor Stuart, Alan Williams, John McKenzie & Terry Holt from the Arthur Rylah Institute  and Goulburn Murray Water.

Contact: Arthur Rylah Institute, 23 Brown St, Heidelberg, Victoria, Australia, +61 3 9450 8600.


Examination of options for removal and disposal of Carp from fishways along the Murray River – including the Williams’ Carp Separation Cage

Key words: European carp, ethical disposal, pest fish, fishways, Native Fish Strategy.

The introduced fish species Common Carp (Cyprinus carpio) has been shown to impact on native fish in many ways, including through direct predation as well as competition for resources such as food, shelter and breeding sites. The “Sea to Hume” fishway program has seen the construction of fishways at sites along the Murray River from the tidal barrages to Hume Dam. While the primary aim has been to improve migration of native fishes, the fishways also facilitate the passage of Carp, potentially providing access to upstream habitats (including spawning habitats) for large numbers of this alien species (Fig 1). The Williams’ Carp Separation Cage is designed to offer a way of removing Carp from fishways without significantly impacting on migrating native fishes.

This research project set out to examine issues and options associated with harvesting Carp at fishways along the Murray River. The study looked at options for harvesting Carp at fishways along the Murray River with an emphasis on the use of the Williams’ Carp Separation Cage (Fig 2), together with the ethical and logistic issues associated with the disposal of Carp.

Carp can reach quite high abundance below barriers to migration such as dams and weirs.  (Photocourtesy of Leigh Thwaites, SARDI.)

Figure 1. Carp can reach quite high abundance below barriers to migration such as dams and weirs. (Photo courtesy of Leigh Thwaites, SARDI.)

How the options were examined: The project team reviewed available literature on methods for the collection and removal of Carp. Design constraints and factors affecting performance were considered, as were recommendations made to enhance functionality and effectiveness. Input from each jurisdiction was considered (to determine capacity and willingness to implement collection programs) as were markets for both human and industrial use (including processing requirements and logistics).


  • The Williams’ Carp Separation Cage was found in most instances to be the preferred method of harvesting Carp. Other methods such as trapping, netting or electrofishing below a weir were considered to have merit for further consideration where the high biomass of Carp may physically impact on migratory native fishes.
  • Harvesting should focus on the migration of pre-spawning adult Carp (about August to December).
  • Disposal methods should favour those that utilize Carp as a resource.
  • While the engagement of commercial fishers is desirable, the commercial Carp fishery is only marginally viable, especially in NSW. It is likely that the involvement of commercial fishers beyond high density sites will have to be subsidized or a coordinated program of collection and storage (e.g. freezers) will need to be implemented.
  • Other options need to be investigated including burial, cremation and composing.
  • Carp must be euthanased in an ethical manner. Currently accepted techniques include the use of anaethetics although with large numbers of fish an ice slurry may be the only practical method. The report also recommends trialling commercially available percussive stunning machines.

A report was produced at the end of the project (Jackson, P. (2009). Final report for River Murray Water, Murray-Darling Basin Authority). This recommends rolling out a coordinated program to harvest Carp along Murray River fishways by expanding first within SA, based on the Lock One experience, and then into NSW. Harvesting should focus on priority sites where high numbers of Carp are present and where fishways will allow access to preferred Carp habitat and potential breeding sites.

The Williams Carp Separator cage provides a potential means for harvesting of Carp at fishways along the Murray River. (Photo courtesy of Ivor Stuart.)

Figure 2. The Williams’ Carp Separation Cage provides a potential means for harvesting of Carp at fishways along the Murray River. (Photo courtesy of Ivor Stuart.)

Take home messages: There is significant potential to harvest Carp at Murray River fishways using the Williams’ Carp Separation Cage but it must be undertaken without any significant impact on native fish migration. A coordinated program with an appropriate level of monitoring is required. The monitoring should include assessments of the impacts of Carp harvesting on upstream Carp populations and recruitment.

Ethical euthanasia of Carp and cost effective disposal remain issues but there are potential solutions. Approval should be sought from relevant Commonwealth agencies for the use of practical destruction measures such as ice slurries and trials using percussive stunning devices should be undertaken. Trials should also be undertaken using commercially available composting bins at sites where commercial fishing is not viable.

Stakeholders and Funding bodies: This research project was funded through the Murray-Darling Basin Authority’s River Murray Assets Division and carried out by consultant Dr Peter Jackson.

Contact: Dr Peter Jackson, Consultant, +61  7  5429 2276+61  7  5429 2276,  Email

From Rainforest to Oil Palms and back again: a Daintree Rainforest Rescue in far north Queensland

Robert Kooyman, Joe Reichl, Edie Beitzel, Grant Binns, Jennifer Croes, Erryn Stephens, and Madeleine Faught

The establishment of Oil Palm (Elaeis guineensis) plantations is responsible for massive rainforest clearing and destruction throughout the tropics of Southeast Asia and beyond, and has captured the attention of conservation organisations around the world. One such organisation is Rainforest Rescue (RR), a not for profit Australian based conservation NGO. Through local and international projects (including in the Daintree region of Australia and Sumatra in Indonesia) RR has undertaken conservation actions that include removal of Oil Palm plantations to re-establish rainforest close to National Park areas.

The rainforest of the Daintree region provides an active window into the evolution, biogeography, and ecology of the southern (Gondwanan) rainforests, and their interaction with Indo-Malesian floristic elements. It has many (ca. 120) federal- and state- listed Threatened, Vulnerable, Of Concern, and Rare plant and animal species and a range of rainforest types.

To achieve restoration of a small (27.6 ha) but important piece of the global distribution of lowland tropical rainforest, RR purchased Lot 46 Cape Tribulation Road in the Daintree area of far north Queensland, Australia in 2010 and, in 2012, secured funding to set the property on its long journey back to rainforest.

The property was partly cleared in the 1960s, first for cattle grazing and later for Oil Palm cultivation. It has a mix of cleared (ca. 11 ha) and early stage natural regeneration (ca. 10ha) areas, bounded on two sides by more intact and mature rainforest (ca. 7 ha). Soils are mostly free-draining sandy clay loams on flat terrain

The on-ground works.  The property was divided into five working Zones as part of the restoration planning process (Fig. 1). Because of a nearby large seed source forest a key objective of the project is to maximise and protect natural regeneration, as well as planting larger openings. Up to 30,000 trees representing 100 species are expected to be planted during the 2-year life of the project, with around 10 ha of natural regeneration interspersed.

Figure 1. Map showing property, work zones (ZONE 1-5), permanent photographic points (Photo point 1-9), location of planting trials (Zones 1 and 2), and primary weed control area (2013) in orange. (Courtesy Google Earth)

Figure 1. Map showing property, work zones (ZONE 1-5), permanent photographic points (Photo point 1-9), location of planting trials (Zones 1 and 2), and primary weed control area (2013) in orange. (Courtesy Google Earth)

Trial tree plantings were undertaken in early 2011 and 2012, and selective weed management (herbicide based grass and soft weed control) began at the same time to optimise natural regeneration prior to identifying and preparing suitable planting sites.

Plantings.  The planting trials were each one hectare in area and designed to test the efficacy of two different high diversity (60-90 species) planting designs. In Zone 1 tree spacing was 2.5m, and in Zone 2 the spacing was 1.5m. Seedlings for rainforest plantings were propagated and grown in the RR nursery in the Daintree lowlands. Seed collection was undertaken north of the Daintree River and included seed collected from the property. A low number of vines were included in the species mix for subsequent plantings.

A total of 90 species have been planted to date. The species mix included some early stage (pioneer type) tree species from genera such as Polyscias (Araliaceae), Alphitonia (Rhamnaceae), Macaranga (Euphorbiaceae) and Commersonia (Malvaceae); and tall fast growing species such as Elaeocarpus grandis (Elaeocarpaceae) and Aleurites moluccana (Euphorbiaceae). The remaining species represented mostly moderately fast growing species, and some slower growing mature phase rainforest species.

Weed control. Where possible, large Oil Palms were removed mechanically, but to protect existing rainforest regeneration many required stem injection with herbicide. Several methods are currently being trialled to determine the most time and cost effective approach to controlling this large and difficult weed.

Late in 2012 and early in 2013 extensive mechanical and chemical weed control was undertaken in Zones 3, 4 and 5 (Fig. 1). This included mechanical clearing of large areas dominated by Giant Bramble (Rubus alceifolius) and other weeds, and some mechanical removal of Oil Palm seedlings on the southern side of the creek that traverses the property (Zones 3 and 4). Follow up chemical control (systematic backpack spraying of glyphosate) was conducted immediately (as required) to complete the site preparation for planting. This was targeted at grasses, broad-leaf weeds, and regrowth of woody weeds.

Monitoring design. Monitoring plots (7 / 50 x 20m plots, each with 10 / 10 x 10m subplots) and permanent photographic points (12 in total, 7 in association with monitoring plots) were established in the five working Zones. Cover, number of species and density will be recorded in these plots at each stratum at 12 month intervals. One monitoring plot was established in each of Zones 1 and 2, three in Zone 3 (including directly adjacent to Zone 4), and two in Zone 5 (in the north of the property; yet to be measured). Zone 4 will be monitored visually and by photo point as it is mostly natural regeneration enhanced by weed control.

Preliminary Results. The first round of project monitoring (year 1 establishment) provided base-line information for future development of the plantings and natural regeneration through assessing canopy cover, leaf litter cover, and a range of other factors that will change over time (Table 1). Informal observations have shown that site dominance was achieved by the trees planted 12 and 18 months ago in Zones 1 and 2.  Substantial numbers of wildling seedlings (of up to 11 species in a plot; and 15 in total) were found in the sites monitored prior to more recent planting.

Mechanical weed control was reported to be extremely effective and the operator was able to minimise damage to existing regrowth of species such as Melicope elleryana (Rutaceae), Glochidion harveyanum var. harveyanum (Phyllanthaceae), Macaranga involucrata var. mallotoides (Euphorbiaceae), Polyscias australiana (Araliaceae), Rhodamnia sessiliflora (Myrtaceae), Alphitonia incana (Rhamnaceae) and Aidia racemosa (Rubiaceae). In combination with the early implementation of broad and targeted spraying this maximised the retention of substantial existing saplings and seedlings.

Project funding will cease in 2014, and control of all weeds and rainforest establishment is expected to be completed in 2015; with only minor weed control required thereafter once canopy cover is established. Monitoring will continue at 12 month intervals and inform future publications.

Acknowledgements: The project is dependent on the generous support of RR donors and the on-going efforts of RR staff in FNQld. Funding for the project was provided by a Federal Government Biodiversity Fund Grant.

Contact:  Robert Kooyman, National Herbarium of NSW, Royal Botanic Gardens and Domain Trust, Mrs Macquaries Road, Sydney 2000 Australia.   Email:;

Figure 2 Mechanical weed control in Zone 3 (January 2013) prior to planting. Note remaining natural regeneration.

Figure 2 Mechanical weed control in Zone 3 (January 2013) prior to planting. Note remaining natural regeneration.

Figure 3. Newly planted trees in Zone 3 (March 2013). Note surrounding natural regeneration.

Figure 3. Newly planted trees in Zone 3 (March 2013). Note surrounding natural regeneration.

Figure 4. Zone 2 planting trial established in late 2011 at 18 months. Tree spacing at 2 - 2.5m.

Figure 4. Zone 2 planting trial established in late 2011 at 18 months. Tree spacing at 2 – 2.5m.

Table 1.  Synthesis of baseline data for natural regeneration, and progress (including planting) up to February 2013 measured on (50 x 20m) permanent monitoring plots (PP), in Zones (1,2,3), by Themes (1 – planting; 2 – natural regeneration). PD – total planted diversity on plot; PS(n) – number of seedling planted on plot; WS – wildling seedlings (0.5-1m in height); WD – wildling diversity; Av. CC(%) – Average Canopy Cover (%); Av. L(%) – Average Litter Cover (%); Av. LBC(%) – Average Log-Branch Cover (%); Av. PCHt – Average planted canopy height (m); dbh – diameter at breast height (1.3m); NR – Number of stems, natural regeneration >1cm DBH; NR-div – Diversity of natural regeneration >1cm DBH; Age (mths) – Age of planting in months. Zone 4 (not shown) has permanent photo points and visual monitoring.

PP Zone Theme PD PS(n) WS WD Av.CC(%) Av.L(%) Av.LBC(%) Av. PCHt NR NR-div Age(m)



1, 2








0.6 – 1






1, 2














1, 2








































Appendix 1 List of main weed species located and treated on the property.

Common Name Species Family Life Form
Sanchezia Sanchezia parvibracteata Acanthaceae herb
Brillantaisia Brillantaisia lamium Acanthaceae herb
Goosefoot Syngonium podophyllum Araceae vine
Toothed Philodendron Philodendron lacerum Araceae climber
Oil Palm Elaeis guineensis Arecaceae palm
Dracaeana Dracaeana fragans Asparagaceae small tree
Sensitive Plant Mimosa pudica Fabaceae creeper
Calopo Calopogonium mucunoides Fabaceae creeper
 Green Summer Grass Urochloa decumbens Poaceae grass
Giant Bramble Rubus alceifolius Rosaceae scrambler
Snake Weed Stachytarpheta cayennensis Verbenaceae herb

Integrated predator management on the south coast of Western Australia

Key words: predators, feral cat, adaptive management, natural area management, threatened species

Allan Burbidge

The Western Ground Parrot (‘kyloring’ to Noongar people) may be the ‘canary in the coal mine’ warning of imminent fauna collapse on the south coast of WA. Over the past decade, this species has undergone a dramatic decline, with the population currently estimated at 140 individuals. This is causing alarm bells to ring, as there is concern that a range of other threatened animals on the south coast may be at risk from the same threatening processes – species such as Gilberts Potoroo, Red-tailed Phascogale, Dibbler, Noisy Scrub-bird, Chuditch, Western Bristlebird and Malleefowl. Considerable progress in fire management strategies for these species has been made by WA’s Department of Environment and Conservation (DEC) over the last few decades, and fox baiting under the Department’s Western Shield program has been in place since 1996. Despite these programs, however, the Ground Parrot population decline continued, leading to the hypothesis that control of foxes has resulted in an increase in the feral cat population (i.e. mesopredator release), with a corresponding increase in predation on native fauna.

Releasing a collared cat (Photo: Emma Adams/WA DEC)

Field trials of Eradicat® baits have been completed under a research permit in Fitzgerald River National Park. Half of the collared cats were killed by these baits, and bait uptake by non-target species was minimal. In 2011 this trial has been extended to include Cape Arid National Park where 19 cats have been fitted with collars, providing direct evidence of bait uptake. Monitoring of predator activity provides additional information on the success of cat baiting. Should this strategy prove effective, the benefits in the wider landscape will be significant.

Feral cat with bandicoot (Photo: WA DEC)

Several clear lessons arise from this work. First, it requires meaningful and ongoing interaction between researchers and managers to carry out robust field-scale adaptive management projects. Second, we have found that institutional barriers such as inappropriate funding timelines can waste the time of project leaders required to continually secure funding and retain skilled staff. Finally, while there is notional support for adaptive management, it is difficult to convince people to support its implementation adequately.

Putting a radio-collar on feral cat (Photo: Emma Adams/WA DEC)

Funding for this project has come from the Department of Environment and Conservation, State NRM, South Coast NRM Inc, Exetel Pty Ltd, Birds Australia and many volunteers. Numerous people have been active in this project including Sarah Comer, Cameron Tiller, Allan Burbidge, Abby Berryman and Deon Utber.

Further reading:
Comer, S., Burbidge, A. H., Tiller, C., Berryman, A., and Utber, D. (2010). Heeding Kyloring’s warning: south coast species under threat. Landscope 26(1), 48-53.

Contact: Sarah Comer (Department of Environment and Conservation, 120 Albany Highway, Albany, Western Australia 6330; tel (08) 9842 4500; email or Allan Burbidge (Department of Environment and Conservation, PO Box 51, Wanneroo, Western Australia 6946; tel (08) 9405 5100; email