Carp separation cages

Carp separation cages


Fishways make it easy for all fish – native and introduced – to move upstream.  Carp (Cyprinus carpio) are highly migratory and often dominate the species using 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.  Most native fish do not jump like Carp, so progress through the fishway and continue swimming upstream.

This project designed a low cost CSC to automatically separate adult carp from native fish.  The season, time(s) of day, environmental cues and biomass (amount) of adult and juvenile carp migrating in fishways was also examined to better target the use of the technology.


The prototype carp separation cage 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 fishes that can be held;
  • holding trapped fish in lower water velocity conditions;
  • exiting native fishes into the weir pool rather than into the fishway;
  • adapting the cage so that it is transferable among exits or different fishways; and
  • more efficiently accessing and removing Carp.

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

Implications for native fish

CSCs on fishways provide opportunities to remove Carp only migrating upstream.  Ideally, the CSC need to be targeted to periods of strong carp movement.  Spring is a critical time for native fish movement so using the cages outside the spring period will maximise catches of carp, but minimise disruption to movements of native fishes.

It is likely that CSCs will increasingly be used as a way of reducing carp numbers in the MDB. For example, the CSC has been modified to suit Carp separation at wetlands (see MD746). It is important, however, to be aware that there are maintenance , carp disposal, and impact on native fishes issues to be addressed. 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. In addition, the applicability of the CSC method for the northern Basin has yet to be determined as there are a number of native fishes that also jump e.g. Spangled perch.


Project MD218 – Carp Separation Cages

Stuart, I. (2009). The Mark V Williams Cage for co-ordinated trapping of Murray fishways. A final report to the Murray-Darling Basin Commission (now Murray-Darling Basin Authority). Kingfisher Research.

Project R2104 – Separation cages for removal of carp from MurrayDarling Basin fishways

Stuart I., McKenzie J., Williams A., Terry Holt T., (2003). Separation cages for removal of carp from MurrayDarling Basin fishways. A report on preliminary tests of the ‘Williams’ Carp Separation Cage’ to the Murray-Darling Basin Commission. Department of Sustainability and Environment

Nicol, S. J., Lieschke, J. A., Lyon, J. P., and Koehn, J. D. (2004). Observations on the distribution and abundance of common carp and native fish, and their response to a habitat restoration trial in the Murray River, Australia. New Zealand Journal of Marine and Freshwater Research 38:  541-552.

Stuart, I.G., Williams, A., McKenzie, J. and Holt, T. (2003). Separation cages for removal of carp from Murray-Darling Basin fishways. Final report of project R2104 to the Murray-Darling Basin Commission.

Stuart, I.G. and Jones, M.J. (2006). Movement of common carp, Cyprinus carpio , in a regulated lowland Australian river: implications for management. Fisheries Management and Ecology. 13: 213-219.

Stuart et al. (2006) Williams’ carp separation cage Final Report to MDBC – Freshwater Ecology, Arthur Rylah Institute for Environmental Research  30

Stuart, I.G., Williams, A., McKenzie, J. and Holt, T. (2006). Managing a migratory pest species: a selective trap for common carp. North American Journal of Fisheries Management. 26: 4.

Barrett, J. (ed.) (2008). The Sea to Hume Dam: Restoring Fish Passage in the Murray River. Murray-Darling Basin Commission, Canberra.

Conallin, A., Stuart, I. and Higham, J.(2008). Commercial application of the Williams’ Carp Separation Cage at Lock 1. Report to the Murray-Darling Basin Commission, Canberra.

Straurt, I.G., Williams, A. McKenzie, J. and Holt, T. (2006). The Williams’ cage: a key tool for removal of carp from Murray-Darling Basin fishways. Final Report to Murray-Darling Basin Commission, Canberra.

Stuart, I. (2008a). The Mark V Williams’ cage for co-ordinated trapping of Murray fishways. Report for Murray-Darling Basin Commission, Canberra.

Stuart, I. (2008b). Co-ordinated monitoring traps and Williams’ carp cages for Murray fishways. report for the Murray-Darling Basin Commission, Canberra.

Thwaites, L., Smith, B., Decelis, M., Fleer, D., and Conallin, A.(2010). A novel push trap element to manage carp (Cyrpinus carpio L.): a laboratory trial. Marine and Freshwater Research, 61, 42-48.

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