Options for managing redfin perch in Lake Purrumbete to improve recreational fishing
Redfin perch is a popular species targeted by recreational fishers in inland waters of Victoria, yet the species is also considered an exotic pest species in Australia that threatens native species and environments.
Lake Purrumbete supports an important salmonid fishery with trophy fish being regularly taken. The lake is regularly stocked with rainbow trout, brown trout and Chinook salmon by The Victorian Fisheries Authority. Since the 1980s redfin perch have become very abundant in the lake and, although the occasional large redfin perch is taken, anglers are often plagued by numerous small fish that have no sporting and eating value. Redfin perch may also be negatively impacting on salmonid populations by both competing for food and preying on juvenile salmonids. While some anglers like to fish for redfin perch in the lake, others loath the species and there has been regular calls for a redfin perch eradication or control program.
This report has reviewed historic and current information on redfin perch in Lake Purrumbete, and potential options for managing of the population in the lake. These included:
- Biological methods (predator introduction, genetic manipulation and control with infectious pathogens)
- Chemical methods (piscicides and pheromones)
- Physical removal (trapping, netting and fishing).
Effective management of redfin perch may be best achieved by employing a combination of strategies. While there is some evidence to suggest that the presence of predatory species (i.e. brown trout and Chinook salmon) has influenced the redfin perch population in Lake Purrumbete, physical removal through a concentrated netting or trapping program may have a more rapid and pronounced impact on numbers.
Being a relatively small and enclosed waterbody with minimal connectivity to adjacent waters, controlling redfin perch in Lake Purrumbete is more realistic and technically feasible than in open river systems. This view is based on international experiences indicating that concerted fishing in lakes has caused substantial declines of redfin perch populations.
Reducing redfin perch numbers in Lake Purrumbete may improve the quality of fishing through improved productivity leading to increased growth rates and therefore an overall increase in the average size of fish in both salmonid and redfin perch populations.
Controlling redfin perch in Lake Purrumbete will, however, require the development of a long-term management strategy as population reduction may be short-lived due to the risk of recolonization and rapid recovery under favourable conditions. Regardless of the strategies employed, consideration should also be given to their impact on the environment and other species, including salmonids, and public perceptions.
The next steps in development of a redfin perch management strategy for Lake Purrumbete should include following:
Meet with key stakeholders to discuss the management strategy and a framework for implementation. This consultation process may include a risk and decision analysis approach to canvas opinions of stakeholders and experts, and assess the risks, consequences and indicative cost of the proposed control options to achieve the desired outcome of the management strategy. This consultation stage will also seek support (in-kind and funding) to undertake the next trial management project.
Research into biology and ecology of redfin perch in Lake Purrumbete
Attempts to successfully target redfin perch removal will be greatly assisted by improved knowledge of the species behaviour and movement patterns. Removal of fish by trapping and netting may be increased by targeting specific stages of the life cycle, at certain times of the year and at specific locations when and where vulnerability to capture may be increased, for example, targeting mature fish at spawning sites during the spawning season.
Efforts to manage redfin perch may be assisted through modelling the outcomes of different management strategies to identify their various effects on the population. Modelling may provide estimates of the fishing effort (and therefore cost) required to reduce the population, as well as forecast changes to population structure.
Redfin perch management project
Outcomes from the stakeholder consultation phase may identify a number of management options for trialling in Lake Purrumbete. A pilot scale project will need to be undertaken to assess the effectiveness of these options in reducing redfin perch numbers. This project will:
- Use existing models to estimate effort required to reduce population size
- Identify behaviour and movement patterns of redfin perch that facilitate capture
- Test the efficacy of different traps and nets in capturing redfin perch
- Determine spawning seasonality and identify spawning sites
- Monitor changes in the size and structure of the redfin perch population as management options are implemented
- Monitor changes in the salmonid fishery.
- Implementation of a redfin perch management strategy for Lake Purrumbete will directly contribute to the value and long-term sustainability of Lake Purrumbete salmonid fishery and may have application in other enclosed waters where redfin perch are a problem.
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