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.
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.
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 Peter.Jackson@westnet.com.au