Getting the Jump on the Infamous Silver Carp: A Q&A with Edward Culver

Instead of sturgeons, we are going to talk about some new research being done on the infamous silver carp.

I am happy to introduce a coworker of mine down here at the National Great Rivers Research and Education Center (NGRREC℠) in East Alton, Illinois, Edward Culver (See Figure 1).

Edward Culver

Figure 1: Ed Culver with a lovely paddlefish caught during routine monitoring. The fish was released unharmed soon after photo was taken.

Ed is an Aquatic Ecologist working for the Illinois Natural History Survey and the University of Illinois in Urbana-Champaign. This post features the research he and his supervisor, Dr. John Chick, are doing on the effects of electrofishing on the injury rates of fishes.

  1. What is the goal of your research? What question or problem do you hope to answer or solve?

We wanted to see if the use of electrofishing injures native and non-native fishes in the Mississippi and Illinois rivers, and whether injury rate from electrofishing varied with environmental factors and/or electrofishing settings. One of the most likely environmental variables to influence the amount of electricity a fish absorbs is water conductivity, thus we wanted to pay particular attention to differences in water conductivity. Water conductivity is a measurement of water’s ability of conduct electricity. Pulse frequency or pulse rate is the number of pulses of electricity per second. It is represented by Hz or Hertz.

Electrofishing is one of the most widely used fish sampling techniques available to fisheries biologists. Through the use of a generator and a control unit, managers can produce electric fields in water that temporarily immobilize fish, facilitating capture. Fish are then measured, weighed, allowed to recover, and released back into the river.

  1. How did you become interested in this topic?

Our original research plan was to conduct experiments examining competition between invasive silver carp (See Figure 2 and 3) and native fishes in their natural environment. Our attempts to conduct these experiments failed because the silver carp we collected had a very high mortality rate. After examining these fish, we found that a large percentage of them exhibited spinal hemorrhaging. Spinal hemorrhaging is rupture of blood vessels within the spinal column and the immediately adjacent muscle tissues that has been shown to be indicative of more serious injuries, such as spinal fractures and vertebral compressions. These silver carp had been collected using electrofishing (Figure 3 and Video 1). I became interested in seeing if this was unique to the silver carp, or if we might also be injuring some of our native species when performing monitoring programs using electrofishing.


Figure 2: Silver carp (Asian carp) jumping out of the water of the Mississippi River. Photo taken by Ed Culver

  1. What are your results so far?

We collected over 400 fish representing 6 species from the Mississippi and Illinois rivers. These were bluegill, channel catfish, freshwater drum, common carp, silver carp, and gizzard shad. Of these species, only channel catfish and silver carp exhibited injuries. 27% of the channel catfish that we collected showed injuries along their spine, and silver carp injury rate was just over 50%. We also found substantial differences in injury rate of silver carp between the two rivers. Injury rates for silver carp was 71% in the Illinois River and 30% in the Mississippi River, and silver carp injury rate was positively correlated with conductivity, temperature, and pulse frequency and negatively correlated with total length. In contrast, the injury rate of channel catfish was similar between rivers and exhibited no correlation with total length, condition factor, conductivity, or temperature.

What this means is that for silver carp as water conductivity, temperature, and pulse frequency increase, the injury rate also increases. As the fishes’ total length decreases, the injury rate increases. However, this does not mean that temperature or the other factors cause the injury, there is only a correlation.

For further information on this study, our research results have been published in the North American Journal of Fisheries Management, Volume 35, pages 1055-1063 titled: “Shocking Results: Assessing the Rates of Fish Injury from Pulsed-DC Electrofishing”



Figure 3: Ed Culver with a silver carp caught during routine monitoring.

  1. Where is your research heading in the future and what obstacles, if any, do you have to overcome?

Right now we are attempting to collect silver carp without using electrofishing and hoping to use the mesocosms (See Figure 4) at NGRREC℠ to compare mortality rates for silver carp collected with electrofishing vs other methods. Although silver carp populations are increasing exponentially in the Mississippi River Basin, they tend to be very sensitive fish that are relatively difficulty to catch with gear other than electrofishing or entanglement gear. Because entanglement gear, such as gill nets and trammel nets, also has a tendency to injure fish, it is a challenge to find an alternative capture method that would allow us to conduct these comparisons.


Figure 4: The mesocausms at work at NGRREC

  1. Is there any other information you would like people to know about your research?

We hope this information will add to the techniques currently employed to prevent the spread of Asian carp to the Great Lakes via the Chicago Sanitary and Ship Canal, a manmade connection between the Illinois River and Lake Michigan. Various management actions are being implemented to contain, reduce, suppress, and remove Asian carp from the Chicago Sanitary and Ship Canal, including the electric barriers that have been installed, all of which use pulsed-DC current.


What a great example of turning lemons into lemonade. Sometimes things don’t happen like we plan, but they can lead to other fascinating avenues. This research is very interesting, and I know I’ll be going to read the full article. Be sure to come back on November 20th for our next post on one of North America’s iconic native birds, the Wild Turkey.

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