From https://www.researchgate.net/publication/234131500_Carp_%28Cyprinus_carpio_L%29_impacts_and_recruitment_in_Australian_wetlands_strategies_for_management?ev=prf_pub

"Carp are benthivorous fish that feed in and on the sediments to a depth of about 12 cm. Benthivores can be the major effect on water quality within a wetland (Cahn 1929; Braband et al. 1990; Meijer et al. 1990; e.g., the source of 80% of phosphorus over two months; Braband et al. 1990). The most profound influences on native fish by carp are probably a result of ecosystem alteration, and possibly also disease transmission (e.g., transmission of dropsy in Europe via parasitic copepods; Welcomme 1984). Carp create an unfavourable environment for the net recruitment of other fish species in slow flowing or still waters by altering prey availability for non-benthic predators (Driver 2002). Carp suspend sediments and probably reduce visibility for visual-feeding fish and clog gill-rakers and gill filaments with sediments (Driver 2002; Shirley 2002). Carp also destroy existing and, in particular, soft-bodied and recolonising plants (Roberts et al. 1995; Swirepik 2000), which would otherwise provide critical habitat for fish feeding, spawning and nursery habitat. Such large-scale loss of plants after carp colonisation in wetlands is well recorded in oral histories (e.g., Lake Cargelligo, NSW, Roberts and Sainty 1997) and is suggested by the negative association between carp and soft-bodied aquatic plants in NSW’s rivers (Driver 2002). Field and laboratory carp studies all suggest that piscivory by carp is unlikely to be a major influence on native fish, although the consumption of fish eggs by carp is perhaps important (Driver 2002; Shirley 2002). Overlap in prey use between carp and native fish species, particularly small species such as galaxids and Australian smelt, has been shown (Khan et al. 2002; Koehn 2004), but there is yet no compelling evidence for competition for similar prey (exploitative competition) that might affect native fish health. Field observations and experiments do indicate that carp can physically exclude smaller fish species and smaller carp from their preferred habitat via overcrowding and behavioural dominance (i.e., interference competition) and might reduce feeding efficiency in visual predators such as redfin (Perca fluviatilis) by increasing turbidity (Driver 2002; Shirley 2002). "

This workshop paper was largely about me trying to promote the practical aspects of my PhD work before it dropped out of my head (Driver 2002); so apologies for the blatant self-citing

Chapter Carp (Cyprinus carpio L), impacts and recruitment in Austral...

Obviously this was all done for the Australian context; but a review of the international literature shows much the same story elsewhere.

Thank you Patrick for such an elaborate answer. You have truly mentioned that carp has similar type of impacts all around. I have gone through some of the literature. Actually, after the introduction of carp this lake has mostly shifted from macrophyte dominant to phytoplankton dominant system.

Can you suggest some restoration measures for the lake as its a major concern now?

.. that is the change you would expect. In isolated systems carp removal is effective. There are examples in Australia and the USA where they have done this; but it would have to be cost effective for your circumstances. Chances are they would come back at some point, so it becomes a maintenance strategy rather than a single fix. You can also decide to fence off some sections to allow macrophyte growth.

Hi!

If we talk about ecosystems, we know that all ecosystems exist in a delicate balance... If carp entered the region and are growing well, something is allowing them to grow well in the area. Find out what this is and try to reduce its quantity. Also look at the problem from the top-down angle and find out what affects or endangers the carp and introduce it into the system and soon you will be free of the carp infestation. But think twice before introducing something into the system as this could have both positive as well as negative impacts. So try on isolated carps in a tank along with other components of the environment for a while till you can get an answer that you are satisfied with and then carry out the best technique on the lake.

Cheers!

Dear Singh

It is very difficult to control a species once it enters an ecosystem, establishes itself and spreads. Currently, no control mechanisms exist for carps (if they become established). No pesticide is identified that would affect the carp, nor we have any information about their vulnerabilities in the course of spawning that could be exploited, nor do we have known about any predatory pressures that would help reduce their populations!

So at the moment, solutions include not only the development of control techniques but also establishment of responsibility so that the managers/authorities remain motivated to achieve what is called “ecological separation” of the invaded ecosystem (for instance, by diverting the canal system so that it is impossible for the carps to move from the place where it has established itself to the adjacent areas). This separation was included as a recommendation of the Aquatic Invasive Species Summit in Chicago in 2003. For instance, efforts are on to build a structure (electrical barrier) and to block other routes to prevent invasive species migration between rivers that parallel the Chicago Sanitary and Ship Canal.

Best

Dola.

Hi The attached brief report I have done for the Ministry of Agriculture in 2009 in Iraq might be useful for you. They were basically asking the same question and you will find a series of case studies and recommendations.

Best Regards

Just to add up, some seismic technologies are under trial at some regions in the US to divert, herd or eradicate aquatic invasive species including the carps.

Please look into the links below:

1. http://www.nrmsc.usgs.gov/files/norock/products/AsianCarp_12.pdf

2. http://www.fas.org/sgp/crs/misc/R41082.pdf

Regarding "Currently, no control mechanisms exist for carps (if they become established). ". Firstly, what does 'carps' mean ..?

The carps/minnows are a diverse group. Many are much less benthivorous than Cyprinus carpio (eg goldfish is more of a water column feeder), and some like grass carp are much more herbivorous. In the USA they also talk about 'coarse fish' from memory. These distinctions matter. A benthivorous species that suspends sediments and nutrients has more of a bottom up, rather than a top down approach .

.. see https://www.researchgate.net/publication/233641767_The_effects_of_size_and_density_of_carp_%28Cyprinus_carpio_L.%29_on_water_quality_in_an_experimental_pond?ev=prf_pub

Also, there are many control mechanisms. Maybe what this is intended to mean is there are few options for complete eradication. This is true, and as discussed only local control or eradication is feasible such as within an isolated waterbody.

Sterile male techniques have also been tested her in Australia (which originates from insect pest management work), herding as well, spring viraemia virus seems to often re-appear as an option (its a problem in aquaculture, and I suspect its virulence is highly population density -dependent) ...

See

http://www.clw.csiro.au/publications/controlling_carp.pdf

https://www.researchgate.net/publication/228028845_Repairing_wetlands_of_the_Lower_Murray_Learning_from_restoration_practice?ev=auth_pub

http://www.feral.org.au/wp-content/uploads/2010/03/Impacts_of_Carpv1.pdf

Finally, stopping the spread of common carp as per the invasive species summit is fine as long as you can stop those areas from receiving periodic flooding. Once carp get in through flood it is hard to reverse the effect.

Article The effects of size and density of carp (Cyprinus carpio L.)...

Article Repairing wetlands of the Lower Murray: Learning from restor...

I don't know if this would help, but I know that light plays a major role in maintaining the biological cycles of organisms. If we were to subject them to flood lights at night for a few nights in a row along with sound vibrations introduced into the water at a certain frequency, this could probably alter their reproductive cycles and later drive the carp away. Also using this technique at regular intervals, you could instill a conditioned reaction in the carp and they would hopefully not return to the region again, even without the use of physical barriers...

@ Dominique: But we should be very careful and not to forget that the same habitat is also shared by other creatures! This should not result in the displacement of native creatures.

@ Dola: That is true, but carrying out the process till the carp have vanished and then restoring the habitat to its initial condition will help the other members of the system to thrive. They would also take the light and short term vibrations as a positive signal as the major predators of the habitat would be removed by them.

Keeping in mind of course that after the carp have left, there would be no further disturbance to the system.

Thank you everyone for great suggestions. It's almost very evident that the most significant thing is to remove the carp form the lake and also prevent them to disperse in water bodies close to the area.

But, I am afraid that removing all the carp is really very much costly. @ Patrick, fencing is a bit more feasible idea but also its not a permanent solution but will give an idea how things will alter atleast in littorals where we can fence off the carp. It may increase at least macrophytic vegetation and macrobenthic diversity there though nutrient dynamics due to the resuspension in other areas will still remain a problem.

@Dominique, there is good point if we can enforce some physiological changes in Carp, but since the lake is of a closed drainage type and gets connected to other local streams only during rains and there is a very less chance of dettering it out of lake. As I have already mentioned it is really sad that it was introduced in lake may be for biocontrol of macrophytes which was once a nuisance in lake but now the conditions flipped the other way.

There are also some methods that are still being studied that involves study of reproductive ecology like radio tracking spawning sites of Carp and then followed by the spawn sabotage which has direct impact on new recruitment in population.

Carp as an invasive species out-competes local fauna for nutrients and space until these native species decline to the point of outright absence.