CARP: Invasive Outlaws
By Danielle Quist, Park Ranger with the Mississippi National River and Recreation Area
On October 1st, a 19 pound silver carp was captured within our park just upriver from Lock and Dam 2 in Hastings, MN. This was a surprise to many, but it wasn’t the first time invasive carp have been caught there. Earlier this summer, on July 17, commercial fishermen under contract by the Minnesota Department of Natural Resources (DNR) caught a bighead carp weighing 40 pounds and a silver carp weighing just under 20 pounds (similar to the one caught in October). Both fish were fertile females possibly carrying thousands or even millions of eggs. These recent and subsequent captures may indicate that there is a chance these invasive fishes are establishing a sustainable population in the area. If this were to happen, these fishes would wreak havoc, causing big problems for human health, the economy, and the environment.
Silver carp and bighead carp are invasive species, meaning they have special adaptions and advantages that allow them to aggressively outcompete most native species. They can tolerate very low oxygen levels, and, although, bighead carp seem to prefer a temperate of around 77° F, silver carp can tolerate a wide range of temperatures from 32-104° F. These adaptions allow the fishes to survive in many different water bodies within the United States. Both species of carp are prolific, reproducing in large quantities. A bighead carp can produce up to 1 million eggs and a silver carp can produce up to 2 million eggs in one spawning season! Therefore, once a few fertile carp are introduced to a lake or river, they can populate it quickly. Also, since neither species is native to the Mississippi River, they don’t have many natural predators to keep their populations in check. Without predators, these fish get extremely large in size. Both silver and bighead carp have been documented to reach sizes of greater than 3 feet in length and up to 70-80 pounds. The largest bighead carp was documented at a shocking 110 pounds! Carp are filter feeders that can eat up 5 to 20% of their body weight in plankton each day.
Plankton, small/microscopic organisms that drift and float within the water column, is an important food source for many of our native fishes, especially during their early life stages. It is sort of like their ‘baby food’. Other fish, such as paddlefish and gizzard shad, depend solely on plankton as their food source during all of their life stages. Invasive carp tend to hog all the plankton causing these native fishes to seek food elsewhere or even die off. Populations of native piscivores, or fish eaters, that rely on juvenile or small fish as their food source, like largemouth bass which prefer to feed on gizzard shad, may also decrease. Invasive carp also harm native mussel populations, which depend not only on plankton as a food source, but on native fish as hosts for their glochidia, microscopic mussel larvae.
Silver and bighead carp not only negatively affect and disrupt freshwater ecosystems and their foodwebs, but they also cause economic and physical harm to humans. Establishment of large, self-sustaining populations of carp on the lower Mississippi River have decreased native fish populations and have forced many commercial and recreational fishermen to seek these fish elsewhere or change professions and/or hobbies. Silver carp jump up to heights of 10 feet when spooked by motorboats or even a canoe paddle. A 20-40 pound jumping fish can cause tremendous amounts of damage to a boat and great harm to boaters and paddlers. Loss of recreational activities, such as boating, paddling, and fishing, caused by the introduction and establishment of these carp populations could greatly harm local economies within Minnesotan communities that rely on these activities to bring in visitors and support local outdoor and recreational shops and jobs.
Silver carp jumping out of water. Silver carps jump when the water is disturbed. Photo courtesy of NPS.
These carp may seem to bring impending doom, but there is hope! Research is currently being done to learn more about the life cycle of these invasive fishes. Methods to stop or at least slow down their advancement up the Mississippi River are being investigated and many are already being applied. Scientists search the water for eDNA, or DNA put in the environment by fish feces, mucus and other parts of the fish. This early detection could help stop huge infestations from occurring and help us create a trajectory of their spread as well as predict where they may end up next. Electronic barriers have been used to zap carp and their eggs, stopping them from traveling from the Illinois River into the Great Lakes. University of Minnesota researcher and professor, Dr. Peter Sorenson and his team from the Minnesota Aquatic Invasive Species Center have found ways to deter carp from entering locks by playing a high frequency noise underwater that scares these invasive fish away when the locks are being used by recreational and commercial boat traffic. Coon Rapids Dam, near Anoka, MN, is being repaired and built up higher in order to create a physical barrier to the upstream advancement of these carp.
On June 11th, President Barack Obama signed a bill calling for the closure of St Anthony Falls Lock and Dam by June of 2015. Without the lock system, the falls themselves would be a natural barrier, since they do reach a height of almost 50 feet, too high for most invasive as well as native fishes to travel up. This seems like a logical solution since there is little boat traffic (both commercial and recreational) that uses this lock, but work and research is being done to help those few who do. A possible portage route is even being investigated for canoeists and kayakers who wish to paddle this section of the river.
Closing the St. Anthony Dam will protect the river upstream from invasive carp. Photo courtesy of Star Tribune.
Not only are preventive tactics being applied to keep carp out of our lakes and rivers, but solutions to eradicating carp from already infested waters downstream are also investigated. These fish don’t have many native predators. However, there may be one important predator that we may be overlooking, us. Current research is being done on ways to make these super bony fish, specifically silver carp, more marketable to humans as tasty treats such as fish cakes, salami, bologna, and jerky. Gastronomists and foodies have been partaking in carp tasting at various locations across the United States, like the “Taste of Chicago”, and to the surprise of many, silver carp have ranked high on many of these taste tests. Most people are usually turned away at the thought of eating carp because there is a misconception that all carp are bottom feeders, but that’s just not the case. Silver carp are filter feeders and therefore feed within the water column. They also have more Omega-3 fatty acids then salmon. These fish can not only be healthy, but pretty tasty if cooked and seasoned correctly. Byproducts such as fish bones, skin, and guts can also be used to create fertilizer. Therefore, the whole fish can be used with little to no waste. Establishing a market for these fish may help eradicate these fish from our infested waterways and help return commercial fishermen (and women) to their jobs. However, there is fear about the long-term effects to keep up with supply and demand which scientists and economists are currently researching.
Boaters can prevent the spread of invasives.
Fishing tournaments have also been another tool used to inform people about invasive carp as well as help deplete some of their populations. Last year’s commercial fishing tournament in Kentucky, entitled “Carp Madness” brought in almost 83,000 pounds of carp! The winning team harvested 28,669 pounds and took home the $10,000 grand prize. Another fishing tournament down in Bath, Illinois has been also gaining some publicity; the Redneck Fishing Tournament provides a more entertaining experience and a few less rules then a commercial fishing tournament. Boaters and fishermen dressed in costume do whatever it takes to catch as much carp as they can, some even using bats to hit one into the boat (or out of the river). There’s even a cash reward for the team that catches the most carp and a prize for best costume.
You can help eradicate and prevent the spread of these invasive fish within our park, too! Make sure to clean, drain, and dry your boat after use, especially after being in infested waters. Don’t move water, bait, or fish from one body of water to another. Sometimes juvenile carp or eggs may be hiding in your bait bucket or be misidentified as a minnow, so it’s best to dispose of unwanted bait into the trash. Invasive carp can hitch a ride in locks when used by commercial and recreational boat traffic, so try to minimize use of these locks to inhibit them from catching a free ride from you. Also, make sure to report sightings of silver and bighead carp to your DNR division, and if you catch one bring it to your local DNR office.