How pro fishing officials catch cheats with polygraphs, metal detectors and good old-fashioned detective work

He calls it his "Columbo moment."

Not unlike the shrewd TV detective, Mark Mandic, the owner of Pro Bass, a professional fishing tournament series, had just uncovered a cheating scandal at one of his high-stakes tournaments in the early '90s in Barrie, Ont.

There was a $10,000 qualifying prize on the line — more, if the fishers who had hidden six huge pre-caught bass in a cage in the reedy narrows then took the grand prize in the championship.

After a competitor alerted Mandic to the caged fish the day before the tournament, he and a marine biologist decided to mark the bass by clipping an eighth of an inch off the dorsal fins so they'd know if anyone tried to pass them off as their catch. The next day, Mandic took the stage as the tournament's MC, with hockey legend Bobby Orr there to help with the weigh-ins in front of an enthusiastic crowd.

"Mark, we got some real nice ones, here," the marine biologist inspecting the fish shouted to Mandic. This, he told CBC News in an interview Thursday, was the agreed upon signal that someone had indeed entered the marked fish in the competition.

"Obviously, the fish are huge. They've taken the lead," Mandic recalled.

"What day did you catch these fish?" he remembered asking the duo onstage as they started to stammer. "Because it couldn't have been today," he continued, before dropping the bombshell that they'd found the fish in a cage the day before.

"They hightailed it. They couldn't have left any faster." Though he said the police showed up, Mandic said he was never sure what happened to the cheaters.

Scandals rock fishing scene

While this incident happened decades ago, the fish tales have kept coming after a series of scandals have rocked the professional fishing circuit, revealing just how prevalent dishonesty is in a sport that can net lucrative prizes for winners and legal consequences for cheaters — when they're caught.

Last week, a fishing tournament in Ohio turned ugly when the director cut open the winning catch of five walleye to find lead weights and prepared fish fillets inside them. A video of the incident went viral, and the county prosecutor is investigating.

And on Wednesday, an angling duo revealed what they say is a history of cheating at a major Canadian tournament, including a competitor allegedly cutting his tape measure to make his catch appear bigger in June.

"It's an eye-opener to every type of sporting industry, whether it's fishing or not," said Victoria Pallotta, event manager for the Competitive Sport Fishing League (CSFL) based in Stouffville, Ont.

The league runs about 30 tournaments per year, and can have cash prizes as large as $30,000, she said.

Polygraphs 'keep people honest'

With that much money as well as sponsorships on the line, the CSFL had already implemented polygraph tests that are mandatory for big title winners, and can also be employed randomly or when a competitor is suspected of cheating. Next year, Pallotta says they plan to start using metal detectors.

"No one ever wants to go into things thinking people are cheating," she said. "But by implementing things like the polygraph test, we like to think it keeps people honest, and because it's also done at random, people know better than to try."

Anglers caught cheating not only face disqualification, but when there's money at stake, they can also face criminal charges.

In 2014, two Alabama anglers were sentenced to a one-year suspended jail sentence after it was discovered that they'd won the Night Owls Fishing Tournament using pre-caught bass, according to WAFF 48, a local news site.

Michael Consul, tournament director with the CFN Fish Off, confirmed with CBC News Thursday that his was the tournament affected by the tape-measure scandal in June. The online multi-species tournament is meant to culminate in a television series which, so far, hasn't been able to air while producers try to determine what can be done with the footage.

Consul and other tournament officials did investigate allegations that an angler had submitted a fish using a tape measure he'd cut to make the fish appear larger than it was. But before they could announce a decision, the competitor in question dropped out, he said.

'We take all allegations seriously'

After speaking with legal counsel, Consul said they decided not to reveal if it had been determined the participant had cut the tape since they dropped out anyway. But he did note that they "take all allegations seriously."

While there's no cash prize with the Fish Off, sponsors provide material prizes to the winners, and also make a cash donation to a children's charity of the winner's choice, Consul said.

Mandic, who is now 65 and lives in Peterborough, Ont., says that while his cheating story is juicy, it's also the only one he's aware of during his 10 years of running Pro Bass.

"People are always lying about fish — the size of the fish they catch or whatever," he said, noting that while most anglers are honest, hardworking people and cheating during competitions is rare, some people still do it.

And when they're caught?

"I think humility is the best punishment."