By Adam Stack

Article Posted: April 4, 2007

Common carp Cyprinus carpio are a fish species that were not originally native to North America. Also known commonly as just “carp”, these large members of the minnow family are native to Europe and Asia (Werner 2004). Carp were introduced to North America in the 1870’s when they were of such high value that their brood stock were protected by fences and guarded.  Today, common carp are one of the most widely distributed fish found in North America (Texas Parks).

Grass carp Ctenopharyngodon idealla (OH DNR) are another member of the minnow family that are presently found in North America but were not native to the continent. Originally native to China, grass carp were introduced to North America to control aquatic vegetation. Triploid grass carp have become a popular method of controlling aquatic vegetation. Grass carp have been known to reach large sizes and consume massive amounts of vegetation on a daily basis, making them a prime candidate for an economical source of vegetation control.

Despite being such a prized and prestigious trophy in European countries, both grass carp and common carp do not have the same popularity in North America. In fact, many regard these fish as a nuisance, and studies are finding that these non-native fish could be impacting our ecosystems in a negative way. Throughout the duration of this paper, I will discuss what studies have shown regarding the ecological effect of carp within North American waterways.

IMPACT OF GRASS CARP AND COMMON CARP ON NATIVE FISH POPULATIONS

Common carp and grass carp have been said to be a threat to native species of fish. Reasons that lead people to believe carp are a threat to native fish range from general competition of resources and habitat, the destruction of substrate, to interfering with aquatic ecosystems from the depletion of resources such as vegetation.

A study conducted in 1997 compared turbidity levels and catch rates of largemouth bass Micropterus salmoides (Werner 2004) in experimental ponds where common carp were present. Turbidity levels were found to be significantly higher in ponds with common carp, as opposed to ponds without a presence of common carp. Carp create turbidity by a few different mechanisms, including resuspension of sediments while bottom feeding, excretion of nutrients and the consequential spike of phytoplankton biomass, and through vegetation destruction which can result in resuspension of sediment by the wind (Dibble1997).

The study found that ponds with the presence of common carp yielded a lower angler catch rate than ponds without the presence of common carp. Two different hypotheses were put into consideration to explain the decrease in catch rates with the presence of carp. One hypothesis considered was that the increased turbidity was the factor that accounted for the decreased catchability of largemouth bass. The other hypothesis considered that common carp population densities reduced largemouth bass population densities which lead to decreased angler catch rates (Dibble 1997).

Population density comparisons of largemouth bass in ponds containing carp and ponds devoid of carp showed little difference. However, angler catch rates differed significantly in ponds with a carp population and ponds without a carp population. Therefore, the study concluded that turbidity created by common carp was ultimately the reason for the lower angler catch rate due to the decreased visibility and low light conditions. Low light and low visibility, both caused by high turbidity, conditions have been proven in the past to decrease the reactive distance between visually feeding fish and their forage (Dibble 1997).

IMPACT OF VEGETATION CONSUMPTION BY GRASS CARP       

As previously noted, grass carp were originally introduced to North America for aquatic vegetation control. A triploid carp, which is sterile, is the popular choice for aquatic vegetation control. The grass carp is practical for such an application because it is an economical choice, as opposed to chemical vegetation control. Grass carp are also effective for the duration of their lives, as opposed to annually applying herbicides.        

Grass carp can pose an ecological threat. A study conducted on various lakes in Washington state revealed varying levels of effectiveness regarding vegetation control by grass carp. 19 months prior to stocking the lakes with grass carp, submersed macrophytes were found to be completely eradicated in 39% of the lakes, 42% of the lakes showed no vegetation control, and 18% of lakes showed an intermediate level of vegetation control. In the lakes where submersed macrophytes were eradicated, a higher turbidity level was found than in the lakes with intermediately controlled and uncontrolled submersed macrophyte levels (Bolding 2002).                                                             

The study concludes that it is a risky procedure to use grass carp as an aquatic vegetation controller due to the difficulty of establishing an intermediate level of vegetation control. Water bodies that cannot withstand complete vegetation eradication should not utilize grass carp as a means to control aquatic vegetation. Larger lakes are even more at risk when utilizing grass carp for vegetation control due to the potential for vegetation eradication, increased abiotic turbidity, and the difficulty of manipulating the grass carp population (Bolding 2002).

Grass carp utilized for aquatic vegetation control would be a more safe and practical application for privately owned ponds or small lakes. Population control is much more feasible and the potential for environmental harm through migration is eliminated if only utilized in private and isolated waters (Bolding 2002).

CONTROLLING COMMON CARP POPULATIONS

Common carp are increasingly becoming more of a threat to North American aquatic ecosystems due to their increasing population number. Numerous ways have been tested to control the populations of the common carp, in order to ensure native and more desirable species are able to thrive, and resources and habitat are sustained.

An effective method for capturing common carp has been established using an instrument known as a big-M trap. Features that make the trap so effective are ability for one person to set the trap and its unique design of floating netting that increases vertical fishing height to over 2 meters. The big-M trap was shown to be most effective when baited with cotton seed soaked in molasses. This trap is effective at both night and day time, with no major differences between catches at either time (Schwartz 1986).

Another means for controlling carp populations can be achieved through Antimycin-impregnated bait. Antimycin-impregnated bait is a poison that attracts carp to consume it, which later results in the mortality of the fish. Amounts of the poison must be consumed by carp accordingly to their weight. If the carp do not obtain enough of the poison, mortality will not occur. This method is most effective when the water body is drawn down to a lower level to concentrate the fish to increase the likelihood of consumption (Luoma 1994).

Other methods for population control of common carp include electric barriers, lake draw-down to induce winter kill (Berry 1995), and selective traps made specifically for carp (Holt 2006). It is difficult to establish a flawless means to control common carp populations due to the effects on other species, migratory routes to different water bodies, and large areas to manage, but many methods are being established to attempt to control populations.

CONCLUSION

Many people fear the effects common carp and grass carp may have on our aquatic ecosystems and our fisheries. Fisheries managers have taken action in controlling their populations. If left uncontrolled, they truly do present a formidable threat to our fisheries and ecosystems. Not only can carp damage aquatic ecosystems, they can alter waterfowl habitat which will ultimately lead to more environmental damage.

Something that does trouble me is the fact that other introduced species that could also alter our fisheries and ecosystem have gained popularity and have taken a higher priority than our established and native species. An example of this can be found in Pennsylvania. Longnose suckers Catostomus catostomus (Werner 2004) have been considered for addition to the endangered species list (U.S. EPA). The same waters that these endangered fish inhabit, a trophy trout program has been established (PA DNR). Neither brown trout Salmo trutta (Werner 2004) or rainbow trout Oncorhyncus mykiss (Werner 2004) are native to the north-eastern United States, yet the Pennsylvania Department of Natural Resources still have established a program where they allow trout to inhabit the same environment as the native and weaning longnose sucker population.

Instead of establishing sustainable populations of introduced fish, currently existing populations of introduced fish that pose a threat to the ecosystem should be managed in order to attempt to maintain equilibrium within our natural ecosystems. Trout may be a popular sportfish and regarded as a table delicacy, but establishing their populations for the simple satisfaction of humans should be a priority that finishes second to maintaining our natural ecosystems.

All content is expressed solely by Adam Stack, through his experience. All photos and words are his.

Literature Cited

Berry CR Jr., Verrill DD. 1995. “Effectiveness of an electrical barrier and lake drawdown for reducing common carp and bigmouth buffalo abundances.” North American Journal of Fisheries Management 15:137-141

Bolding B., Bonar SA., Divens M. 2002. “Effects of triploid grass carp on aquatic plants, water quality, and public satisfaction in Washington state.” North American Journal of Fisheries Management 22:96-105

Dibble ED., Drenner RW., Edwards MC., Gallo KL., Rieger KE. 1997. “Common carp affect turbidity and angler catch rates of largemouth bass in ponds.” North American Journal of Fisheries Management 17:1010-1013

Holt T., McKenzie J., Stuart IG., Williams A. 2006. “Managing a migratory pest species: a selective trap for common carp.” North American Journal of Fisheries Management 26:888-893

LandBigFish. 2001-2007.

            <http://www.landbigfish.com/fish/fish.cfm?ID=23>

Luoma JA., Marking LL., Rach JJ., 1994. “Development of an antimycin-impregnated bait for controlling common carp.” North American Journal of Fisheries Management 14:442-446

Ohio Department of Natural Resources. 2005. 28 March 2007

<http://www.dnr.state.oh.us/wildlife/Fishing/aquanotes-fishid/grscarp.htm>

Pennsylvania Fish and Boat Commision. 2007.

            <http://sites.state.pa.us/PA_Exec/Fish_Boat/fishpub/summary/trophytrout.html>

Schwartz FJ. 1986. “A leadless stackable trap for harvesting common carp.” North American Journal of Fisheries Management 6:596-598

Texas Parks and Wildlife. 2007. 23 March 2007 <http://www.tpwd.state.tx.us/huntwild/wild/species/crp/>

U.S. Environmental Protection Agency. 2007. 30 March 2007

<http://www.epa.gov/fedrgstr/EPA-SPECIES/2007/March/Day-08/e4081.html > 

Werner, Robert G. Freshwater Fishes of the Northeastern United States. Syracuse: Syracuse University Press, 2004.