construction and refurbishment of earthen irrigation channel banks

The disadvantages of a biological control program can be:• extremely expensive to set-up (sometimes $millions)• lengthy to set-up (often over ten years)• potential risk of the disruption of the native environment• strict guidelines to be metPelicans and cormorants can be significant predators of carp, however, only smaller(more manageable) sizes of carp are preyed upon. It is possible that foxes may preyon the larger sizes of carp. However, it is unknown how effectively naturalpredators control carp.The use of viral agents for biological control, such as the Spring Viraemia CarpVirus (SVCV) is considered to be unreliable for technical, commercial,conservation and logistic reasons and some sectors of the public have expressedconcerns about the use of viral control agents.Potential molecular approaches include immuno-contraception to reduce carpfertility and the introduction of a fatality gene into the carp population which canthen be triggered chemically or by some other means. However, there are currentlyno biological or contraceptive control agents suitable for use against carp, and genetechnology is not yet at a stage where it can be used for carp control. Thereforecarp management in the immediate future will rely on environmental rehabilitation,physical removal, poisoning where appropriate, and most importantly, reducingtheir spread.23.5.8 Prevention of re-infestation of irrigation systemMost irrigation systems control inflow and outflow of water through structures.Therefore the potential exists to modify these structures to restrict the movement ofcarp. Currently there is a lack of information about carp movement patterns thatwould enable the viability of modifications to inflow/outflow structures for carpmanagement to be determined.Fish barriers have potential as cost-effective, environmentally friendly methods ofcarp management.23.5.8.1 Mesh BarriersWire Mesh barriers have been successfully used to prevent carp from migratinginto irrigation systems from lakes and rivers.The disadvantages of this method are:• Debris will be trapped at the mesh barriers which would then require cleaningand monitoring.• Fish eggs can travel through wire mesh screens. Larger fish can be eliminatedonly until eggs hatch and develop into mature fish.• Flood flows can overtop structures re-introducing new populations of carp.Further options to improve screen design could be investigated.Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 23-23