Attracting carp so their presence can be accurately assessed

Note: This project is the combined second phase of three previous projects: Developing food attractants for silver carp that can be used to induce aggregation and control them, Testing whether carp can be located using Judas fish: a new behavioral tool to locate aggregating invasive fish so they might be tracked and/or removed, and Determining the ability of two approaches to measure eDNA to reliably quantify the abundance of invasive common carp in Minnesota lakes. 

MAISRC researchers are currently working to prevent adult bigheaded (Asian) carp from migrating upstream from the lower Mississippi River using acoustic deterrents and modifying gate operations. Because this needs to be very strategic and efficient, MAISRC must have extremely accurate information on the abundance of adult invasive carp in the area.

This project aims to remedy the deficiencies currently associated with eDNA by developing new techniques to cause predictable aggregations of adult invasive carps. This will facilitate their accurate measurement using eDNA and pheromones or alternately their being trapped and removed.

This research will examine the possibility of causing aggregations using both sexual and feeding cues.

In order to develop reliable and practical ways of using sexual stimuli to find carp, researchers will artificially induce female sexual behavior and sex pheromone release using hormone implants. They will then determine if they can track these aggregations using eDNA measurements and sex pheromone concentrations. They will also test the possibility that a Judas fish (a sterilized fish equipped with a tracking device) could be used both to drive an aggregation and/or track it. Additionally, researchers will test whether food or a synthesized compound could drive aggregations of carp.


Following data collection in 2015, it was found that food was able to drive large aggregations of common carp which we successfully measured using eDNA and pheromones. This baiting scheme has now been perfected and in some cases, a third of the population of mature common carp were able to be attracted using food, all while measuring abundance with a new level of sensitivity, precision, and accuracy. Pheromone-releasing Judas fish were also evaluated for their ability to attract other carp. This research has now informed a pilot study of attracting Silver carp in Illinois using both methods.

These studies have demonstrated that while sex attractants (pheromones) have promise for attracting (and controlling) male common carp when they are present at low densities, food attractants have exceptional promise to attract and control both male and female carps when they are present at high densities. Additionally, food can be deployed at a relatively low cost. Work testing how light can be used as a repellent for carp is promising and ongoing. Plans are proceeding to field-test the sound-air curtain-light deterrent system that was developed in the lab. Tests are planned in the Mississippi River. Native species (Lake Sturgeon, golden shiner, channel catfish, and bluegill sunfish) will be tested as well.

As of January 2019, new work looking at the ability of an optimized sound to deter carp when combined with an air curtain and light system, was underway in the MAISRC Containment Lab. These unified systems are consistently able to stop close to 99% of all bighead and common carp in the laboratory with no indication of habituation (diminished efficacy with time). It was found that a sweeping (pulsed) sound (provided by Fish Guidance Systems Ltd) is more effective than a continuous broadband sound (outboard motor). Additional studies have shown that native lake sturgeon and bluegill sunfish are little affected by the sound stimulus alone (unlike carp which are deterred by sound) but are deterred by sound when combined with bubbles. Initial additional tests with strobe lights alone are promising as they show species-specific effects dependent upon background lights levels.

Final outcomes:

This project developed several tools that can manage and control all species of invasive carp in Minnesota. First, we developed ways using both food and sex pheromones to attract and measure the presence and density of carp using the environmental DNA (eDNA) they release to the water. This technique is superior to traditional netting because it can be performed in any habitat or water of any depth, including at low densities that are otherwise unmeasurable. eDNA can also determine carp gender. Second, we developed a deterrent system comprised of sound, light and air curtain that is 97% effective in the laboratory and could safely and effectively prevent invasive carp from swimming upstream through navigation locks in Mississippi River. If this deterrent system were to be paired with attractant-based eDNA surveillance methods in specific locks and dams with gates that are also adjusted to stop carp, it is extremely likely that enough carp could be prevented from passing through these locks and dams that the remainder could be removed by targeted commercial fishing. Field tests of the deterrent system are now underway.

The first invasive carp deterrent system in the world is now in place in southern Minnesota using the sensory cues we identified. The USGS is now exploring the pheromone and food attractants we developed in the Great Lakes, and the sound/light stimuli we developed are being used at Barkley Dam in Kentucky by the UAFWS with whom we have partnered with.

Phase 1.1: Testing whether carp can be located using Judas fish: a new behavioral tool to locate aggregating invasive fish so they might be tracked and/or removed

This project developed techniques to locate aggregating carp using sterile, sexually active Judas fish to determine if sterilized carp can be rendered sexually active with hormone implants. New sensory tools (e.g. sound playback) will be developed as needed to control the behavior and distribution of adults.

To remove highly mobile and invasive fish such as carp, we must know where they are. The Judas fish technique (tracking a few individual animals to find other members of their group) was developed as a means to locate low numbers of Asian carp in Minnesota waters. This technique has been used with great success in other locations. The first step was developing means to sterilize carp in collaboration with a veterinarian. Later, researchers developed means to track them using radio-transmitters in rivers. Common carp were our primary model but we included work on Asian carp in the laboratory. After initial research, it was determined that this technique would not work well with males competing in the wild. Research is now focused on conducting experiments to determine how to fully feminize sterile fish instead.

Phase 1.2: Developing food attractants for silver carp that can be used to induce aggregation and control them: a new biochemical tool

This project identified and developed chemical food attractants for Asian carp that could be used with poison nanoparticles being developed by the USGS. Understanding how to optimize food and sex pheromones in the lab will allow researchers to develop ways to apply sensory cues to attract carp and stimulate aggregation.

In addition to knowing where these fish are, researchers would ideally also be able to stimulate them to aggregate in specific locations using attractants. Common carp and Asian carp are social animals that tend to aggregate, so this approach has great promise. Initial work with radio-tagged common carp has already demonstrated that these fish will quickly locate aggregating groups of conspecifics in the winter, when the entire group can be located and removed by seining (this is also known as the Judas fish technique). Researchers also aim to develop food and/or sex pheromone attractants to stimulate aggregations outside of the winter months.

Phase 1.3: Establishing and implementing eDNA as a molecular technique to assess the presence of Asian carp in large Minnesota rivers

This project demonstrated that initial 2011 measurements of Asian carp eDNA in the Mississippi River were almost certainly fallacious and attributable to poor markers. New measurements conducted after by MAISRC researchers and later the USFWS have been unable to confirm these measures. MAISRC studies also developed new and better techniques to measure eDNA. The release and decay rates researchers calculated for eDNA by bigheaded carp have added even greater resolution and significance to eDNA techniques and ongoing studies which can now be interpreted with much greater certainty. Our finding that eDNA release is closely correlated with feeding activity is especially germane; now, future eDNA measurement will be much more relevant.