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HARPERS FERRY, IOWA — Commercial fisherman Ralph Mohn is old enough to remember when bald eagles didn’t exist along the upper Mississippi River.

He served in Thailand during the Vietnam War and returned to the far northeastern corner of Iowa in 1967 when the insecticide DDT was still in use. He wanted to fish for a living and took a liking to the hoop nets and trotlines utilized in the area’s catfish trade.

“Using one hook is a horrible way to catch a fish,’’ Mohn said last week while filling orders inside his long, low-slung fish market on Great River Road.

As similar operations in Minnesota, Wisconsin and Iowa have disappeared, the Mohn family has remained in business by forging a successful relationship with Asian community food stores in the Twin Cities. At least 85% of the daily catch at Mohn Fish Market is purchased by retailers along University Avenue in St. Paul and in other Asian enclaves in the metro area. Customers place their orders each Monday and the family delivers fish each Thursday in their own refrigerated box truck.

“It’s kind of a dying occupation, but we’ve got really good customers,’’ said Vickie Jones, the daughter of Ralph and Diane Mohn.

Vickie raises a family of her own in between daily outings on the river in her no frills aluminum boat. She and her brother, Joe, target catfish, sheepshead, carp, buffalo and sand sturgeon. Any incidental catches of walleye, northern pike or other game fish are released according to the limits of their commercial license. They team up with a few family friends to produce 1,000 pounds of fish per day, sometimes more.

Vickie sets out on the Mighty Mississippi nightly, equipped with long heavy trotlines laced into rectangular wooden boxes to avoid tangles. Bare hooks hang from the lines at 5 foot intervals, tipped with ivory soap, clams, fish parts, minnows, leeches, night crawlers or other bait depending on the season. The lines sag toward the bottom, anchored and attached to a buoy at the surface.

Early the next morning she’ll gather the catch from the 500 hooks she sets out. Eight to 10 fish per line of 50 hooks is a good harvest. The team’s fishing boats are rigged for live transport and the fish are relayed into the market’s large aerated indoor tanks until they’re processed. Filled with fresh groundwater, the tanks hold 3,000 pounds of live fish.

Ralph Mohn said water levels on the river have been consistently high for the past four years, making it tougher to find fish. Lately there’s been no sheepshead, but the average size of catfish seems larger this year, he said.

At their USDA-inspected market, the family fills orders in the backroom. They sell their fish whole, dressed, fileted, smoked or pickled. For customers who maintain aquariums in their stores, the Mohns also offer live catfish, $1 per pound. The most expensive item on their menu is smoked sturgeon at $4.25 per pound (when available). Catfish cheeks sell for $3.50 per pound.

The cinder-block smoker at Mohn Fish Market is 8 feet high and it’s loaded twice a week with 250 pounds of carp steaks and 300 to 400 pounds of catfish pieces. Another delicacy, pickled sucker fish, is sold in small jars, prepared 50 gallons at a time. The market’s retail counter is in a small room at the front of the store that doubles as the office. Ralph and Diane live in the house behind the market.

They don’t advertise their store, partly because they’re often scrambling to keep up with wholesale orders. Ralph said there’s been a little slack lately because of the pandemic.

“Our local fish fry business is lost right now,’’ he said.

At age 73, Ralph isn’t part of the regular fishing team, but he’s heavily involved in production inside the market’s backroom. He’s a legend in the Driftless Area of Minnesota and Wisconsin for identifying the first nesting pair of eagles at the Minnesota-Iowa line after DDT was banned in 1972.

Now, with an abundance of eagles flying over his fish market every day, he recalls how he used to feed the pair one fish a day as he passed near their nest on his boat. “They probably didn’t need it, but I’d throw it up on the ice anyway,’’ he said.