Preliminary investigation of an “Achilles Heel” for control of Redfin Perch in New South Wales

Key words: Perca fluviatilis, Redfin Perch, invasive species, physical removal, control strategy, Native Fish Strategy.

Threats and Impacts: Redfin Perch (Perca fluviatilis) is an alien fish species that has been established in Australia for more than 150 years. Although a popular recreational angling target in some regions, it has a range of deleterious impacts on native fish, through predation and competition for resources, and as a vector for a virus (epizootic haematopoietic necrosis virus). Despite the threat posed by this species, there are major deficiencies in current knowledge and policies in regards to controlling existing populations and responding to new infestations. In New Zealand and Australia the control of Redfin Perch has been found to be most effective in small lakes and ponds using physical removal techniques such as nets and traps, as well as mid-water trawling and electrofishing at night.

Project objectives and methods: The objectives of this project were to:

1. undertake a detailed literature review of species biology to identify weaknesses that could be exploited in control programmes;
2. conduct field trials of potential control techniques;
3. complete an investigation of behaviour and movement using acoustic technologies; and,
4. provide recommendations for a future control programme, including scoping of sterile feral technology.

This study included a detailed literature review of Redfin Perch biology to identify any potential weaknesses that could be exploited in control programs. Field trials were then performed in an impoundment (Suma Park Reservoir) on the central tablelands of New South Wales, known to contain an abundant population of Redfin Perch, and a riverine site in the Gwydir catchment. The trials were designed to investigate the effectiveness of physical removal of Redfin Perch using a combination of electrofishing, panel (gill) netting (with and without herding), fyke nets and clover-leaf traps with several attractants (laser lights, glow sticks, magnets and berley). The study also used underwater acoustic cameras (DIDSON) to examine Redfin Perch behaviour in response to each of the attractants. Separate trials were undertaken in winter and summer. Additional field trials were undertaken in a riverine site in the Gwydir catchment during summer.

Given the limited understanding of the species movement patterns and the importance of this information to targeting control techniques, an acoustic tagging study was undertaken in Suma Park Reservoir.

Figure 1 A cloverleaf trap such as those used during field trials (Photo courtesy of Dean Gilligan)

Figure 2 The focus species for this study, Redfin Perch (Photo courtesy of Dean Gilligan)

Findings: The review of Redfin Perch biology highlighted several key aspects that could be exploited in future control programmes:

•  timing of reproduction – target removal prior to or during spawning events;
• inducible sterility – sterile feral technology;
• spawning behaviour – removal/reduce availability of spawning substrate;
• self regulation of populations – bio-manipulation or sterile technology; and,
• schooling behaviour – target control efforts.

In the removal trials, catch rates in fyke nets and cloverleaf traps were relatively low across all three trials (winter and summer in reservoir and summer in river) with standard panel nets and electrofishing being the most effective methods. The clover-leaf traps were not effective at catching Redfin Perch, either with or without attractants within the traps. Catch rates in cloverleaf traps and fyke nets were too low to draw any conclusions relating to improvements in catch efficiency resulting from the use of the attractants trialled. However, assessment of the response of Redfin to the various attractants using DIDSON imagery revealed that glow sticks and lasers do have the potential to be used as attractants, particularly at night.

The acoustic telemetry study indicated that most fish occupied the downstream end of the dam, with only up to two individuals spending extensive periods of time within the upstream reaches of the impoundment. Overall, fish spent 90% of the time within the top 10 m of the water column, possibly due to lower dissolved oxygen concentrations below this depth.

Lessons learned and future directions: Overall this project has resulted in the compilation of valuable information on Redfin Perch that can contribute to its future management. In particular:

• passive fishing techniques/traps that rely on luring/attracting fish into a certain area (e.g. clover-leaf traps) are not very effective;
• they appear to be much more susceptible to being caught in nets that target/intercept fish while moving (fyke and panel nets);
• electrofishing is effective in the short-term and on a small scale, but may not be cost effective/practical in the long term as abundance of the target population declines;
• glow sticks and laser lights were found to be effective attractants at night, but optimal deployment methods need to be established that minimise trap-avoidance of those fish attracted;
• juveniles form large schools, whereas adults were more solitary; and,
• movement data indicates the top 10 m of the water column and areas around the deeper downstream reaches of impoundments are occupied most frequently and may be appropriate areas to target removal efforts. 
  

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

Contacts: Dr Dean Gilligan, New South Wales Department of Primary Industries. Tel: + 61 2 4478 9111, Email: dean.gilligan@industry.nsw.gov.au