ST. PAUL, Minn. (WCCO) — The Minnesota Department of Natural Resources is sharing new details into “Operation Squarehook.” That is the codename of the undercover operation that netted at least 31 people in what is being described as the largest fishing bust in some 20 years.

Those charged are accused of engaging in the illegal commercialization of Minnesota game fish. Ten members of the Red Lake and Leech Lake bands are charged in Federal Court with selling legally netted walleye. That is a violation of tribal code and the U.S. Lacey Act, which strictly prohibits commercial sale of fish and game.

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The two-year investigation discovered that “tens of thousands of walleye” were being netted from Lake Winnibigoshish, Leech, Cass and Red Lakes. The tribal netting itself started as a legal take but violated the law once those fish were put up for sale.

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The last time something this widespread targeted the state’s highly prized walleye was back in 1993. That’s when an illegal commercial fish market led to the eventual collapse of Red Lake’s walleye fishery. Conservation efforts have since led to Red Lake’s recovery.

They’re among the state’s most prized walleye fishing lakes. But for Leech, Winnie, Cass and Red, what started as legal netting quickly turned into an illegal and widespread fish market.

“We had netters and anglers supplying an initial buyer and that buyer then sold to the secondary market,” said the DNR’s enforcement chief, Jim Conrad.

The black market was largely word of mouth, operating out of vehicles and the back doors of some area businesses.

Along with the 10 tribal anglers, another 21 non-tribal buyers and sellers are now facing state charges.

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“It is just as illegal to purchase game fish as it is to sell game fish. Without buyers there wouldn’t be sellers,” DNR commissioner Tom Landwehr said.

But the ecological damage went beyond simply the selling of walleyes. Along with fish cleaning waste, piles of unwanted northern, whitefish and tulibees were discarded in the woods.

It was just over one year ago when Bob Auel discovered a huge pile of rotting fish and entrails in the woods near Leech Lake.

“They cleaned the walleyes which are the best ones and left the rest of the fish to rot – it’s wanton waste,” Auel said.

The black market fillets were sold for only $1.50 – $3 per pound. That compares to $11 to $17 per pound for commercially raised walleye sold in stores. It’s one big reason the poaching ring sold tens of thousands of Minnesota walleye in just the past few years.

“If you engage in this type of illegal activity, at some point we will catch you,” Landwehr said.

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At this point, investigators say the operation was limited to the areas around Leech, Cass, Winnibigoshish and Red lakes. The investigation did not find more widespread commercial sales anywhere else in the state, including lake Mille Lacs.