Adapting Stream Barriers to Remove Invasive Fish During their Seasonal Migrations

This project seeks to develop a system to remove large numbers of invasive common carp during their spawning and seasonal migrations at existing barrier sites in streams in Minnesota. In order to take advantage of carps’ strong migration instincts in spring, this project will include a newly developed fish transport system and an electric fish guidance system.

The electric barrier will be placed in a stream to guide fish toward a chute, at which time they will be channeled into the Whooshh System and removed. This barrier, developed by Procom Systems, is unique because it is a very mild electric field to guide fish rather than stun them, and is portable so it can easily be modified to fit specific study sites. An electric barrier is used so water and debris can still flow freely. The Whooshh System was originally developed to move salmon safely around barriers such as dams in the western U.S., and is now being adapted for removal of carp. Once carp enter the front chamber of the Whooshh system, they are pneumatically pushed through a flexible plastic tube and into a holding pen for removal. This project includes installing and testing the electric fish guidance system, testing and adapting the existing Whooshh system to allow for removal of carp, and laboratory work to optimize both systems.

Final report

The overarching goal of this proposal is to develop a system that can remove large numbers of invasive common carp during their spawning and seasonal migrations at existing barrier sites in streams. Specifically, we will focus on testing and adapting a technology recently developed for salmon in western United States to achieve this goal. This technology, called the Whooshh System, is comprised of an artificial riffle (i.e. a simple fish ladder) that the fish climb and then follow a slight downward slope (slide) into an entry chamber. Once the fish enter the front chamber, they are pneumatically pushed through a flexible plastic tube that can be hundreds of feet long. By doing so, the fish can be safely and quickly transported over dams and other man-made structures to allow their spawning migrations. In case of invasive fish, such as carp, the tube could lead to cages for removal.   Thus, while Whooshh was originally designed to restore salmon populations along the west coast, we will use it to manage invasive common carp in the Midwest. Carp employ similar spawning migrations like salmon.

Common carp (Cyprinus carpio) are the most wide-spread and damaging invasive fish in Minnesota. In the spring, up to 90% of carp migrate from lakes to marshes to spawn. Often, thousands of carp are seen moving through small streams and creeks over the course of few weeks in May and June (Fig. 1). These fish are driven to reach their destinations and are often seen trying to jump over existing stream barriers, which they can usually cross with some effort. If these carp could be removed, many populations could be managed in a sustainable way. Unfortunately, it is difficult to predict exactly when carp will migrate, most move at night, and the ones that are seen at barrier sites during the day scare easily and are difficult to capture. If whoosh systems could be incorporated into existing carp barriers, many thousands of carp could be removed from streams with relatively little effort, which would allow for sustainable management strategies in many locations. Further, Whooshh engineers are currently developing species recognition capacities, which could be used to direct invasive carp into containment while allowing native fish a safe passage across barriers. The direct goal of this proposal is to test and adapt the existing Whooshh system to allow for selective removal of common carp during their spawning migrations. This will be accomplished by conducting field trials during two springs and summers at sites where carp barriers already exist (or where temporary barriers could be easily built) and where spring migrations have been documented in the past. We will also conduct laboratory tests during fall and winter to optimize systems that guide carp into the Whooshh System. Finally, if species-recognition component of the Whooshh System is developed by the onset of the project, we will also conduct laboratory trials to determine if carp can be selectively distinguished from native fish, such as the northern pike (Esox lucius), during spring migrations to remove the former and conserve the latter.  

Our goal from the onset was to develop devices and technologies with commercial applications. Thus, this work focused on developing and testing many prototypes of devices needed to guide and remove the carp, discarding ones that showed little promise or were impractical, and testing further those that showed promise. While our initial intent was to conduct laboratory tests, we were able to switch to field tests, which provided much more realistic results. First, a technology was needed to block migrating carp and direct them into a trap. The portable low-voltage electric systems available commercially was tested for that purpose and shown to be very effective (over 90% carp blocked), easy to deploy and maintain. Then an enclosure had to be designed that was inexpensive, easy to install and durable under high flow conditions. For that purpose, we used PVC pipes inserted into stream bottom through openings in horizontal support beams. While seemingly trivial, this design was quite ingenious as each pipe could be easily adjusted individually to accommodate uneven bottom and scouring. Once these tasks were accomplished, our main challenge was to develop a technology for the carp to swim into the Whooshh system. We tested several designs of floating fish ladders, but none were effective. We also built and tested Archimedes screw in the laboratory, but it also proved ineffective after initial tests. A breakthrough occurred when we decided to use a partially submersed conveyer to remove the carp along with portable electrodes that could be used periodically to crowd the carp over the conveyer and then immobilize them so that they collected on the surface of the conveyer and were then transported out of the stream. This system was successfully tested in the summer 2019 using stocked carp and in spring 2020 using naturally migrating carp. The conveyer can be used to load carp into the Whooshh system, but it can also be used independently to collect the carp from the stream and carry them on land. This technology appears to be ready for commercial applications. Should more funds be available, further tests should focus on perfecting ways to increase the rates with which migrating carp enter the trap (PVC enclosure) and perfecting the system of electrodes inside the trap for aggregating carp over the conveyers.


Project manager: Przemek Bajer

Funded by: Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources; Rice Creek Watershed District; Clean Water Fund

Project start date: 2017

End date: 2020