The term "invasive carp" is used to refer to four species of fish introduced into the United States in the 1960s and 1970s for use in aquaculture ponds. Through flooding and accidental releases, invasive carp found their way into the Mississippi River system and are now thriving in waters of the United States. These four species are similar, but they have unique diets and are found in different locations.
Bighead carp and silver carp are filter feeders that remove plankton from the water and are established throughout much of the Mississippi River Basin. Bighead and silver carp are often collectively referred to as bigheaded carp.
Black carp consume freshwater mussels, snails, and other mollusks. They have a limited but expanding range in the Mississippi River.
Grass carp specialize on eating submerged aquatic plants and are widely distributed in the United States, with growing numbers of reproducing populations, including in the Sandusky River in the Lake Erie watershed. Of the four species, grass carp is the only species being used as a bio-control agent for nuisance aquatic vegetation throughout much of the United States.
The following series of maps show the expanding range of all four species of invasive carp in rivers throughout the United States. Data points shown on the maps are documented sightings or records from the USGS Nonindigenous Aquatic Species (NAS) Database. Below, the map on the left shows the spread of bighead carp (red dots) throughout rivers of the United States from 1981 to 2020. One bighead carp was captured in Lake Erie in 1995 and two were captured in 2000. The map on the right displays the expansion of silver carp (orange triangles) over a similar time period.
The maps below show the expansion into the United States of grass carp (green squares on the left) from 1972 to 2020 and black carp (yellow diamonds on the right) from 2003 to 2020.
Invasive carp are fast growing and compete with native aquatic species for food and habitat resources. In areas where invasive carp are abundant, they harm native fish communities and interfere with commercial and recreational fishing. Silver carp are easily disturbed and will jump out of the water, often damaging boats and injuring passengers.
The USGS conducts invasive carp research focused on early detection, risk assessment, and the development of control tools and strategies. The goals are to prevent the establishment of invasive invasive carp in the Great Lakes and to reduce their impacts in the Mississippi River Basins and elsewhere.
Managers can use the information, tools, and strategies for early detection of invasive carp in order to control the population once their presence has been discovered. New detection and control tools are designed to also be effective for other invasive species and application in many different regions.
This USGS research focus addresses the goals of the Great Lakes Restoration Initiative (GLRI), a multi-agency collaboration started in 2010 to protect and restore the Great Lakes.
As a member of the Invasive Carp Regional Coordinating Committee (ICRCC), which guides invasive carp efforts, the USGS works closely with federal and state agencies, Canada, and other partners to address high-priority invasive carp issues and to provide science for management decisions.
The USGS has gained extensive knowledge of invasive carp biology and life history over the past 30 years. Life history refers to the pattern of events related to an organism's survival and reproduction. That knowledge guides the design, development, and application of control strategies. This is essential for developing approaches in line with modern principles and practices of integrated pest management (IPM).
IPM is a process used to solve pest problems while minimizing risks to people and the environment. Use of an integrated and adaptive approach helps managers focus monitoring and control efforts. These multiple areas of research are interrelated.
Effective management of any invasive species relies on early detection. Detection of invasive carp using traditional capture gears is difficult when their populations are small because these fish avoid nets and are sensitive to the sound of boat motors.
The USGS has contributed to the development and improvement of new approaches to monitor invasive carp, even in low abundances. These new approaches detect deoxyribonucleic acid (DNA) shed from invasive carp from water samples that are collected from streams and rivers, known as environmental DNA, or eDNA.
To monitor the extent and growing population within the Mississippi River Basin, samples from water bodies are regularly collected and analyzed for the presence of invasive carp eDNA.
Working with industry, the U.S. Fish and Wildlife Service (USFWS), and state agencies, the USGS has tested and validated a commercially available kit for rapid detection of invasive carp using eDNA.
These point-of-use kits, described in more detail in this USGS podcast, allow conservation managers and law enforcement agencies to quickly and efficiently detect the presence of invasive carp eDNA in bait tanks on-site and make timely decisions to prevent the spread of invasive species.
Field testing indicates that fish and wildlife law enforcement officers without any prior experience can use the kit to detect the presence of a single, minnow-sized silver carp commingled with more than 10,000 fathead minnows in a large fish tank.
Additional testing, accompanying directions, and protocols for sample collection have been developed. Fish and wildlife law enforcement agencies in several states have had the training to collect these samples and are utilizing these units today.
Researchers at the USGS and the Missouri Department of Conservation are exploring the use of eDNA as a tool for monitoring population density. In coordination with a large-scale invasive carp removal effort in Creve Coeur Lake, Missouri in February 2018, water samples were collected both before and after the removal effort. The concentration of eDNA in these samples were then analyzed to determine if the density of invasive carp changed after the removal effort.
Preliminary data results indicate that at sampling locations, eDNA detections of bigheaded carps in Creve Coeur decreased from March 2018 to April 2018.
eDNA monitoring can detect changes in local populations in response to management actions, such as large-scale removal efforts like the Modified Unified Fishing Method which is explained in more detail in the control section.
Scientists perform risk assessments to estimate the likelihood that a species may invade, spread, or cause economic or ecological damage; to identify ecosystems or habitats most likely to be invaded; and to estimate other risks associated with species' invasions. Risk assessments are part of the IPM process and help managers focus their monitoring and control efforts.
Part of the risk assessment process involves researching invasive carp life history, which enhances agencies' ability to effectively target the species and control their spread. Invasive carp eggs hatch in less than 2 days.
The grass carp larvae seen in the background photo are 160 hours old, or 160 hours past fertilization.
For some species, such as black carp, there is minimal information on current population status or biology within their introduced ranges. Scientists work with collaborators from other agencies and the public to gather information on range, growth, development, diet, and habitat use.
Examples of early life history projects involve raising black carp in a bio-secure facility to gather information on physical characteristics of eggs, directionality and swimming capabilities of larval fish, and developmental rates.
Biology and life history research has led to the development of models, tools, and strategies to better understand the risk of invasive carp establishment and survival in new areas.
The Fluvial Egg Drift Simulator (FluEgg) is a particle transport model that simulates egg and larval drift and dispersion during the critical period between spawning and gas-bladder inflation.
Invasive carp spawn in rivers during high-flow events in areas of enhanced turbulence. Invasive carp eggs must remain in suspension in the water column as they develop and hatch while drifting downriver.
Once hatched, larvae can swim vertically, but continue to drift downriver until the gas bladder inflation stage at which point the larvae begin to swim horizontally and seek out nursery habitat.
At typical temperatures, the entire process from spawning through hatching, gas-bladder inflation, and dispersal to nursery habitats takes less than a week.
In collaboration with the University of Illinois at Urbana-Champaign, the USGS developed FluEgg to allow scientists and natural resource managers to identify rivers that are suitable for invasive carp spawning. In collaboration with the University of Toledo, USGS researchers used the FluEgg model to identify spawning areas and then verify and validate the method. These models and methods help managers assess risks of invasive carp and evaluate the efficacy of control measures to disrupt spawning.
FluEgg is applicable in areas where invasive carp are present and areas that have not yet been invaded. FluEgg can also be used to model egg drift and dispersal of other species, provided the egg density and diameter are known.
The USGS also provides collaborative platforms for partner agencies to share, visualize, and analyze data, allowing managers to make informed decisions as part of the Integrated Pest Management process.
One of these data sharing applications, the FishTracks Telemetry Database (an example of which is seen in the background), includes data from fish that are surgically implanted with acoustic telemetry transmitters.
The transmitter tags are monitored by a network of telemetry receivers deployed throughout the Mississippi and Ohio River basins.
Telemetry data can provide information about how far fish are moving in a river system, changes in the distribution of a fish population, and, when viewed with flow and water temperature data, how river conditions influence fish movement.
Telemetry monitoring of fish movement is used in a variety of invasive carp research, including investigating the upstream passage of fish through lock structures at high-head dams (which serve as potential pinch-point locations for preventing further range expansion) and evaluating the effectiveness of control tools like carbon dioxide barriers.
Telemetry data are used in applications like the Spatially Explicit Invasive Carp Population (SEICarP) model. The U.S. Fish and Wildlife Service and the USGS, in support of ACRCC objectives, are continuing the development and refinement of the SEACarP model to help maximize fishing harvest effectiveness with the goal of reducing numbers of adult invasive carp in targeted areas of the Illinois River.
The SEACarP model serves as a decision support tool to inform the optimal location and timing of fishing efforts on the water, and to help identify additional key invasive carp population and life history data collection needs.
As part of the risk assessment process, the USGS is assisting the Tennessee Valley Authority (TVA), the Fisheries Division of the Tennessee Wildlife Resources Agency (TWRA), and the U.S. Army Corps of Engineers (USACE) Nashville District, in evaluating control measures to reduce or prevent further invasive carp passage throughout the Tennessee River System. The states of Alabama, Mississippi, Tennessee, and Kentucky, as well as the U.S. Fish and Wildlife Service, also participated in the assessment.
The USGS facilitated a Structured Decision Making (SDM) workgroup with these partners in a process that prioritized ten lock and dam locations (shown here) throughout the Tennessee River System. The SDM process has also been successfully implemented for grass carp in Lake Erie.
The silver carp population in Pickwick Lake, between the Pickwick Landing lock and Wilson lock on the Tennessee River, is considered to be the leading edge of invasion in the Tennessee River System. The primary management goal is to minimize the number of carp upstream of this invasion front, or upstream of Wilson Lock.
Using a Structured Decision Making approach helps partners to identify the most strategic locations to install deterrent technologies. Suitable invasive carp spawning and habitat areas for the reservoirs and major rivers of the Tennessee River System were also modeled using FluEgg.
The workgroup reviewed data on different barrier technologies at each strategic location and evaluated a range of effectiveness scenarios aimed at slowing the upstream migration of invasive carp.
The workgroup considered a range of deterrent options and combinations, including lock closure, no action, acoustic deterrent systems (ADS), bioacoustics fish fence (BAFF), carbon dioxide (CO2), and electricity. Hypothetical installation scenarios, like the example shown here at Wilson Lock, were used as a reference during the SDM process.
For more details on these types of deterrents, continue to the next section, Control Tools.
In collaboration with partners, USGS scientists continue to develop and test containment and control tools and technologies for invasive carp to prevent their future spread, reduce their population levels, and minimize their effects.
The integrated pest management approach investigates options for combined implementations of tools in strategic locations.
Underwater sound technology is being tested as a tool to deter further spread of invasive carp. Bigheaded carp react strongly to underwater sounds, like the frequency of an outboard motor, whereas many native fish have little to no response. This suggests that underwater sound could be used to specifically deter bigheaded carp from entering an area while still allowing native fishes to move freely.
Studies are also underway to evaluate the use of sound to move fish and improve capture and removal. Researchers are installing and testing a large-scale Acoustic Deterrent System (ADS) at the entrance of Lock and Dam 19 on the Mississippi River at Keokuk, IA to deter invasive carp from moving upstream through the lock.
Bathymetry and lidar (light detection ranging) surveys were conducted to provide a detailed picture of the lock chamber and river bottom to aid in the installation of an ADS at Lock and Dam 19.
These types of hydroacoustic surveys are also being used to collect more information about the aquatic habitat conditions preferred by invasive carp to further inform control and removal strategies.
A bio-acoustic fish fence (BAFF) has been installed at the Barkley Lock and Dam in Kentucky. The BAFF is a multi-sensory system that consists of a curtain of bubbles, light, and sound aimed at deterring invasive carps from moving into the lock entrance without impeding commercial and recreational boat traffic.
A three-year field trial of the BAFF system, led by the U.S. Fish and Wildlife Service (USFWS) and developed by U.K.-based Fish Guidance Systems, is currently underway. Testing this deterrent technology is a collaborative project between multiple partners, including the USFWS, Kentucky Department of Fish and Wildlife Resources, U.S. Army Corps of Engineers, Tennessee Wildlife Resources Agency, and the USGS.
Carbon dioxide (CO2) is being evaluated as a chemical control tool for invasive carp. Infusion of CO2 into water has the potential to deter invasive carp movements. Experimental applications of this method have found promising results under controlled settings.
In 2019, the USGS and USFWS obtained a Section 3 registration label from the U.S. Environmental Protection Agency to administer CO2 as a fishery chemical to deter invasive carp movement.
Current studies are investigating the use of CO2 as a behavioral deterrent, to reduce fish passage through navigational locks and block their spread into new areas.
Bighead carp, whose movement is monitored with telemetry tags in this pond trial, move away from areas with higher CO2 (yellow-orange background) created by injecting CO2 into the water.
Carbon dioxide is also being evaluated as a lethal control to kill and remove large quantities of invasive carps in a short period of time. This control tool could greatly improve removal efficiency, particularly in areas where invasive carp abundance is high.
The vast majority of approved chemicals for management of aquatic invasive species are applied as a solution, exposing both target and non-target animals (e.g., native species) to the same toxic dose. To reduce risk to non-target organisms and the environment, the USGS and partners are developing and testing chemical control tools, or toxicants, that can be applied as part of a species-specific integrated pest management program.
Ongoing research includes 1) identifying invasive carp life history and physiological characteristics that can be exploited to optimize delivery and enhance the selectivity and sensitivity of chemical controls, 2) determining optimal application strategies (such as timing and methods) to maximize control, and 3) registering and producing these types of chemical controls.
Researchers are investigating the use of Antimycin A as a targeted-toxicant delivery system. The chemical control is designed to be eaten by invasive carp but is smaller than what most native fish feed on.
To test the species selectivity of the toxicants being developed, dye is included in the bait formulation. Fish that consume the bait turn blue, like the grass carp seen in the background photo, while non-target fish that did not ingest the bait remain their normal color.
Options for field experiments to test these toxicants as effective control tools are now being investigated.
Other aspects to developing chemical controls for invasive carp include integrating these chemicals into baits that take advantage of their feeding behaviors and/or food preferences. The USGS is developing baits that consist of ingredients invasive carp will readily consume, such as corn feed and alfalfa.
Bait attractants aimed at aggregating invasive carp, such as certain mixtures of algae to which invasive carp are strongly attracted, can be used to facilitate capture and removal. Those favored by invasive carp can be deployed through "feeding stations" deployed to help draw invasive carp into nets and traps.
The video above shows a school of silver carp swimming toward a powdered algal mixture and quickly consuming it.
The next phase of chemical attractant research will focus on screening other potential attractants for all invasive carp species, including grass carp, using an electro-olfactogram (EOG) assay. Attractants that elicit an electrical response will be further tested to evaluate the species' behavioral response to the stimulus.
If a strong behavioral response is observed, field tests will be conducted to determine whether the stimulus can effectively concentrate carp for more efficient removal. When techniques for concentrating carp are shown to be effective, those methods will be shared with interested management agencies so that invasive carp can be harvested more efficiently.
Prior to using chemical controls in the environment, regulatory approval from state and federal agencies is required. As part of the registration process, the USGS assesses whether a compound being developed (such as Antimycin A or carbon dioxide) is effective, safe to humans, and reduces the risk of exposure to non-target species.
Degradation data is also required for these chemical controls to evaluate their potential fate and effects in the streams, rivers, and lakes where they are applied.
After chemical controls have received regulatory approval for use in aquatic environments, the USGS and partners work with industry to manufacture the compounds. As restricted-use pesticides, these controls may only be applied by state-certified pesticide applicators.
Adapted from a traditional fish harvest technique in China, the Modified Unified Method uses herding methods and a variety of nets to drive invasive carp into contained areas where they can more easily be harvested.
The USGS and partner agencies are modifying these techniques to work in North American waters for efficient, large-scale removal of invasive carp.
In a unified method, block nets are used to create compartments into which fish can be driven. Electrofishing and boats equipped with underwater speakers herd carp into compartments, which are then blocked to prevent them from escaping. This process is repeated, clearing each compartment, until the fish are concentrated into a harvest area.
Other adaptations to the method include using side-scan sonar to determine the location of schools of fish. These modifications have made mass removal events highly successful - in one example conducted in the 300-acre Creve Coeur Lake in Missouri, 240,000 pounds of invasive carp were harvested.
The USGS is also developing decision support tools to help fisheries managers plan and coordinate Modified Unified Fishing events. Boat movements and net deployments, tracked with Global Positioning System (GPS) devices, are visualized in tandem with invasive carp harvest and movement data to continually improve these large-scale removal efforts.
The negative effects of invasive invasive carp in North America are far reaching and have real potential to expand and intensify. A wide variety of organizations are working to keep these invasive fish out of the Great Lakes and other aquatic ecosystems, and control them in their current locations, including the Ohio River and Mississippi River Basins.
Contributions by the USGS to inform integrated pest management are particularly important, especially the objective evaluation of tools for control. Numerous USGS Science Centers will continue this important research, coupled with education, synthesis, publication, and other forms of knowledge transfer that inform management solutions.
Published 04/23/2021.
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