Asian carp being eaten by native fish, new studies find
Asian carp are showing up in the diets of some native fish. This is encouraging news for big rivers that carp have already invaded, but it does not change the fact that the Great Lakes are at great risk of invasion.
The Midwest Fish & Wildlife Conference was held last Feb. 8-11 in Indianapolis, Indiana. The first conference began 75 years ago to provide scientists and other natural resource professionals an opportunity to discuss fish and game management issues with minimal political influence.
Topics reflect current trends in research across the Midwest as well as significant management challenges. Not surprisingly, this year Asian carp emerged as a key theme. In fact, 10 posters and 34 oral presentations stretching over almost three days focused on aspects of Asian carp biology, monitoring, and control.
Let’s be clear. We are nowhere near a “magic bullet” that will wipe out bighead and silver carp (the two species of greatest concern). Instead, a number of tools currently under investigation might be used in the future as part of an Integrated Pest Management (IPM) strategy. These tools include removal netting, commercial fishing, microparticle toxins, seismic waterguns, and manipulation of stream flow to encourage spawning in poor locations or settling of eggs.
Another tool that has potential to limit, but not eliminate, the damage caused by silver and bighead carp, is predation by native predatory fish. This only works if native fish are feeding on carp, and two presentations at the Midwest conference focused on research related to this issue.
Cory Anderson, a graduate student at Western Illinois University (WIU), presented the results of diet studies conducted on the Illinois River in conjunction with collaborators at WIU, U.S. Geological Survey, Illinois Natural History Survey (INHS), and Illinois DNR and with funding from the Upper Midwest Environmental Science Center. Stomach contents from 1500 native predatory fish caught in the LaGrange Reach in 2014 were examined. Asian carp were found in the stomachs of channel catfish, flathead catfish, largemouth bass, white bass, black crappie, white crappie, and gar species.
Small Asian carp were extremely abundant following a large spawning event in the summer of 2014. When any food source is abundant we expect that predators will take advantage, but some predators were actually going out of their way to select Asian carp. Gar were particularly fond of Asian carp, which accounted for half of all fish found in gar stomachs. White bass were also selectively preying on small carp and had a high abundance of them in their stomachs.
One big limitation of native predators is that most are unable to eat adult Asian carp. After all, it takes a fish with a very big mouth to swallow a 20-30 inch long carp. Tad Locher and James Lamer of WIU looked for a situation where a large predatory fish might feed effectively on adult silver carp. They found such a situation in a backwater of the Mississippi River near Alton, Illinois.
Blue catfish top out at over 100 pounds and are native to the Mississippi River basin (but absent from the Great Lakes). Adult blue catfish are opportunistic predators but often roam open water in search of shad and other baitfish. In the Alton backwater, blue catfish were finding lots of silver carp.
Stomach contents from 68 blue catfish measuring 22-40 inches long revealed that adult silver carp were the top prey item in terms of weight. The average age of silver carp eaten by blue catfish was 3.9 years. According to other studies, female silver carp typically mature at age 3 or 4.
Although blue catfish are not native to Michigan waters, another large fish-eating catfish is. The flathead catfish dwells in large, warm rivers of southern Michigan and often weighs 10-30 pounds. Other top predators like Great Lakes muskellunge, which are now being reintroduced to west Michigan rivers drowned rivermouth lakes, might also have the ability to prey on mature Asian carp up to a certain size.
Even so, the best strategy for preventing a Great Lakes invasion is to stop it before it starts. Once an aquatic invasive species establishes a foothold it becomes nearly impossible to eliminate it by any means in a system as large as the Great Lakes and its connected waterways. Michigan State University Extension news archives provide a wealth of additional information on biology, prevention, and control of Asian carp and other invasive species.