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 negative impacts on native fishes. Despite the threat that the species poses, there is a lot that we don’t know about this species or how to control existing populations and respond 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. This study included a detailed literature review of Redfin perch biology to identify any potential weaknesses that could be exploited in control programs.

A field trial was then performed in an impoundment (Suma Park Reservoir) on the central tablelands of New South Wales, known to contain an abundant Redfin perch population. The trial was designed to investigate the effectiveness of physical removal of redfin 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 movement patterns for this species and the importance of this information to targeting control techniques, an acoustic tagging study was undertaken in Suma Park Reservoir.

Findings:

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

• target removal efforts during or prior to spawning events
• explore use of sterile feral technology
• remove/reduce availability of spawning substrate
• explore use of bio-manipulation or sterile feral technology
• exploit schooling behaviour

In the removal trials, catch rates in the 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 trialed. Assessment of the response of redfin to the various attractants using DIDSON imagery, however, 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 were active both at night and during the day. The majority of individuals occupied the downstream end of the dam, with only one/two 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; this could be due to lower dissolved oxygen concentrations below this depth.

Key messages:

Overall this project has compiled 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 at catching Redfin.
• the species appears to be much more susceptible to being caught in nets that target/intercept fish whilst 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 are 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.
• 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.

Management of Redfin perch will require an integrated management approach just the same as carp, with links provided in the Related Projects section to the sorts of strategies and approaches currently being used to manage this pest species.

Full report here: Faulks, L., Rodgers, M., Timmins, M. and Gilligan, D. (2011). Preliminary investigation of an Achilles Heel for redfin perch, Perca fluviatilis, control in New South Wales. Draft final report, Fisheries NSW.

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