Minnesota DNR fisheries research biologists hold large flathead catfish netted for a
three-year study to determine population and size structure in a portion of the Minnesota River.
Big Cats in the Minnesota River
By Keith “Catfish” Sutton
This northern river may be one of the country’s best places to catch a whopper flathead.
The Minnesota River flows 330 miles from the South Dakota/Minnesota border at Big Stone Lake, through St. Peter and Le Sueur, and joins up with the Mississippi River in Minneapolis/St. Paul. Many folks drive over or alongside the river every day without realizing that some huge flathead catfish lurk there.
“Catfish live down to the Granite Falls Dam, so they can’t get above it. That’s 250 miles from Granite Falls down to the Mississippi River where flathead catfish can be caught,” said Minnesota River specialist Tony Sindt with the Minnesota Dept of Natural Resources (DNR). “They’re abundant throughout that entire stretch. Flathead catfish like hanging around log jams and deep holes behind the current breaks behind trees. They let the current bring food to them, so they don’t have to chase it down.”
Angling pressure on these fish has increased in recent years, prompting Minnesota DNR fisheries research biologists to conduct a three-year study to determine just how big these flatheads grow and to identify ways to protect and maintain this trophy fishery.
At four sites along the river between Mankato and Shakopee each August, biologists have netted fish, measured them and implanted microchips to identify them before returning each fish to the water. The capture and recapture of these fish over those three years allowed researchers to estimate the population and determine size structure, growth and survival rates.
The median size of sampled flathead catfish was estimated at 29.8 inches and most were five to 15 years old. Population estimates determined that there are 144 fish per river mile longer than 20 inches, 80 fish per mile longer than 28 inches and 48 fish per mile longer than 34 inches. These results indicated a very abundant flathead catfish population relative to others nationwide, with a high percentage of large fish.
But the existence of trophy-size fish depended on a 91-percent annual survival rate that allowed unusually fast-growing individuals to reach old ages. Any substantial decrease in that survival rate would put the population’s size structure at risk, so conservative regulations are necessary and remain in place to maintain the opportunities these big cats offer river anglers.