Cyprinus carpio – An Invasive species?

By Dave Votaw

For at least the last 100 years environmental scientists have been concerned about invasive species in North America.  Ask any Midwestern fisherman if he knows any invasive species and he’ll probably list zebra mussels, round gobies, and asian carp without hesitation.  Taking the long view, these are truly invasive species that are going to dramatically affect warm water ecosystems if left unchecked.  And these three are far from alone, which begs question:  what is an invasive species?

Here are three of many definitions quickly found on the Internet:

These three definitions illustrate that the term invasive can be defined simply or more complexly, and it is not immediately obvious which organisms, in our case fish, are invasive and which are not.

Carp fishing today may be the most popular form of fishing on the planet.  Google carp fishing and you get 1.3 million hits, and North American fishermen are just beginning to catch on.  In Fisherman likes to refer to our time as the Bronze Age because of the tremendous explosion of smallmouth bass across the continent.  The next handful of decades may well come to be known as the Carp Age; they are literally everywhere in North America – Canada to Mexico, Maine to Hawaii – much to the delight of a growing number of anglers of every stripe.  Wade a Midwestern creek or river on a regular basis and you will see them, quietly gliding by your waders, oblivious to your presence until spooked, making the bass and sunfish you’ve been catching look like fry in comparison to the carp’s incredible size in even small flows.  And every fisherman has an opinion too:  hated trash fish that ruins game fish habitat, or fabulous new sport fish and table fare.

The introduction of the common carp (Cyprinus carpio) to North America is not complicated.  The fish’s native range is the Caspian and Aral seas of eastern Europe and western Russia.  The exploitation and decline of native North American fish stocks had reached a point by 1870 that the U.S. Government established the U.S. Commission of Fish and Fisheries to address the problem, particularly in light of the need to feed the growing population.  The Commission selected the common carp over native fish for replenishing American fish stocks due to the species ability to reproduce and live in a diverse variety of habitats; the fish was also considered a delicacy in other parts of the world.  In 1877 the Commission imported common carp from Germany and began propagating and distributing them as food fish with the assistance of state fish commissions.  The active stocking of common carp, including mirror and leather carp, continued for approximately 20 years, with the fish often being released from railroad tank cars at bridge crossings.  The U.S. Commission discontinued stocking in 1897 because common carp had been distributed to almost every state and territory and were well established.  Efforts to eradicate carp began almost immediately.

Common carp are most at home in lakes and impoundments, as well as sluggish, somewhat turbid streams and wetlands.  Typical lifespan is approximately 15 to 20 years.  Trautman, in Fishes of Ohio, notes that common carp are most abundant in streams receiving sewage or substantial runoff from agricultural land, which describes almost every flow in the Midwest.  However, he found them to be rare in clear, cold waters and streams of high gradient.  Common carp are known to eat almost anything, including detritus from plants, vegetation, plankton, crustaceans, gastropods, and significantly, fish eggs.  Their feeding behavior is active, often disturbing and uprooting vegetation and sediments and thus increasing turbidity.  The impact of this behavior can be extensive and dramatic; in addition to adversely affecting the growth of aquatic vegetation, important to the life cycles of everything from zooplankton and insects to fish and birds, silt re-suspension can disturb the spawning of native fishes, inhibit sight feeding species, and decrease photosynthesis.  Under these conditions phytoplankton (algae) populations tend to increase due to the increased release of nutrients from sediments and the decrease in zooplankton predation.  While the negative impact of common carp on biodiversity and water clarity has been regularly documented in shallow lakes and ponds, large and deeper systems seem to be less dramatically affected; also, rivers and streams appear to have been studied less extensively than lakes and ponds.

Carp management and eradication efforts have been underway in the U.S. for over 100 years, which gives some immediate insight into their ineffectiveness and the incredible adaptability of this fish.  These efforts have included physical barriers, harvesting, and rotenone poisoning.  State regulated commercial fishing may hold the greatest potential for controlling common carp populations.  In Australia, concern over expanding common carp populations has led to the testing of a potential reproduction control plan - the introduction of “daughterless carp,” one component of Australia’s National Management Strategy for Carp Control.  Daughterless carp, as the name implies, are genetically manipulated to produce only male offspring despite breeding normally.  With fewer and fewer females produced with each succeeding generation, a population can become mostly male.  The expectation for the river where this technology will be tested is a sharp reduction in carp numbers within 20 – 30 years of release.  This technology is species specific and will not affect native fish.

In North America, the common carp seems to have been incorporated effectively and harmoniously into many aquatic ecosystems, particularly rivers and larger lakes; they have become an integral part of the food web.  History demonstrates that this species is here to stay despite its detractors and efforts to control or eliminate populations.  Is Cyprinus carpio still an invasive species today?  Federal and state government agencies and conservation groups do continue to list the common carp among invasive species, and the fish remains disreputable among a majority of anglers.  Fishermen should ask themselves if they’ve ever chased brown trout in the U.S.  If so, they’ve fished for and admired a species that came from Europe and is not native to North America – an invasive species.  The National Park Service notes that native species can be invasive also.  Consider largemouth bass in California and Mexico, smallmouth bass in Oregon, walleye pike in South Dakota, northern pike in Colorado, salmon in the Great Lakes, and so on.  These are examples of enormously popular sport fish enthusiastically pursued in waters outside their native ranges – invasive species.

It would seem that carp populations need to be controlled, but may as well be enjoyed as the amazing, difficult to catch sport fish that they are.  If you catch one this season, keep it, take it home and prepare it with one of the recipes found on the Web, for example at www.activeangler.com.  Try the recipe for carp tacos there, as well as other preparations!  If you don’t like the fish as food, use it for fertilizer in your vegetable garden or feed it to the cat.  There are plenty more where that one came from!