Fisheries crews trying to remove Asian carp in Pool 8

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By Ted Pennekamp


Fisheries crews from Wisconsin and Minnesota began a plan on April 5 in Pool 8 of the Mississippi River to get rid of Asian carp. The crews gathered near La Crosse to try a technique new to the Upper Mississippi River.

The modified unified method combines herding and netting to drive and concentrate fish from a large area into a small zone for removal.

The effort is focused upon taking out bighead, silver and grass carp, which are invasive species that have wreaked havoc in the Illinois, Missouri and Ohio river systems and are spreading north in the Mississippi River.

The work is being spearheaded by the Minnesota DNR, said Tim Miller of the La Crosse District (pools 7 and 8) of the U.S. Fish and Wildlife Service. The work is being done by the Minnesota DNR, the Wisconsin DNR, the U.S. Geological Survey and the U.S. Fish and Wildlife Service.

Miller said this is the first time the modified unified method has been used in Wisconsin or Minnesota waters. He said the method has previously been successful in Asia and in some southern states in the U.S.

The intensive effort was designed as part of the response to the capture of 39 silver carp and 12 grass carp in the La Crosse area in March of 2020. Miller said commercial fishermen caught the fish in their nets in March of 2020 and the various agencies involved in this new project would like to eradicate the destructive carp so they can’t reproduce.

Jordan Weeks of the Wisconsin DNR Mississippi River Team-Fisheries Management said the modified unified method  (MUM) was developed in Asia where the people created a systematic way to gather and harvest these species efficiently so they can eat them.

“The fish are moved or herded using electricity and sound into consecutively smaller cells created by shoreline and block nets until the cell is small enough to use a seine to surround and gather the fish,” said Weeks. 

Miller said sometimes a “Judas fish” has previously been tagged with a transmitter so that the crews can more easily locate a school of Asian carp. Also, Asian carp DNA shows up in water samples, so crews know where to look. Side scanning sonar can also be deployed. In addition, Miller said the crews know what types of habitat the fish like, especially during times of cold water temperature. Thus, the best times for herding and netting Asian carp are in the spring and fall.

Jordan Weeks said all of the sites will be in Pool 8 backwaters and side channels. Cat Gut Slough and 1-90 Bay are a couple of the sites. 

“Work is planned to begin April 5 and run until all eight sites are complete,” said Weeks. “We will not be working weekends in order to avoid recreational boat traffic. The work should be done by April 16 at the latest.”

Weeks said there will be an average of 10 boats for the MUM work. Occasionally there will be more. The Wisconsin DNR boats will each have a crew of two people but there are some larger boats involved which will have more staff.

Pool 10 has not been sampled, but Weeks said it is likely that silver and bighead carp reside in Pool 10, but are most likely there in very low numbers.

The capture of 39 silver and 12 grass carp near La Crosse last year marked the largest number of Asian carp caught to date in Wisconsin. Weeks said it was the impetus for the MUM work. 

“To date, the MUM has only been used on waters that contain massive silver and bighead carp populations,” said Weeks. “The work in Wisconsin is designed to see how the method works when few carp are present. We are using a proven method to attempt to assess the presence/absence and relative abundance of silver and bighead carp in Pool 8. We do not expect to capture large numbers of either species.”

Silver and bighead carp have been found in all Wisconsin waters of the Mississippi River and in the St. Croix River below Taylors Falls, Weeks said. These captures have typically been single fish, with a couple of exceptions.

“We planned this MUM with help from MNDNR, USFWS, USGS, and other partners to get baseline data regarding the relative abundance of silver and bighead carp in Pool 8 of the Mississippi River,” said Weeks. “While some invasive carp have been captured in Pool 8 previously, we do not think there is a large population. Assessing these locations will help us better understand if that assumption is true.  In addition, this work will help us develop a plan for combating invasive carp should they become more numerous. After the first event in Cat Gut Slough, we caught zero invasive carp while capturing many native game and non-game species.”

Asian carp are known for their voracious food habits and tendency to jump, startling boaters on the lower portions of the Mississippi River.

The jumping of the silver carp (also known as head butting carp) can potentially injure boaters, but that is not the main concern regarding their movement up the Mississippi River. The main concern about silver carp and bighead carp (which are two separate species of Asian carp), is that they reproduce and grow very rapidly once established in an area and they also are huge eaters of plankton and plants which other species, such as small forage fish and sport fish, need. 

In the Illinois River, for example, Asian carp have outcompeted, and to a large extent, displaced native fish species.

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