A Hawkes Bay fisherman who caught a monster Marlin has a bigger fight on his hands to get his $48,000 prize after being told he had failed a lie detector test.

Dean Young caught the 136.6kg Marlin on his dad's boat, Super Scheme, which won him the top prize at the Mega Fish competition, run by the Hawke's Bay Sports Fishing Club, over Waitangi Weekend.

Mr Young, a 47-year-old former police detective, hauled in the 136.6kg fish on the first day, winning the tournament for the biggest marlin over 125kg.

He said he was stoked to win the top prize - a brand new Isuzu ute valued at $48,000 offered up by the Bayswater car dealership in Napier - which he planned to sell so the proceeds could be split between the boat's four crew.

That was until the event promoter David Baty from OddsOn Promotions told Mr Young he had to undergo a lie detector test before being awarded any prize.

Six weeks after the fishing competition, Mr Young was flown to Auckland to undergo the polygraph test - administered by private investigator Craig Gubbins from Personal Verification.

Mr Baty paid Mr Gubbins to carry out the test at the OddsOn Promotion offices in Mt Wellington on March 17.

Mr Gubbins has been contacted by Newstalk ZB/NZME but has refused to comment on the test or the results due to privacy agreements.

Later that day, Mr Young was informed he had failed the test and wouldn't get his hands on any prize money or the ute.

He said it was a total mystery to him why he had to undergo a lie detector test. He had never heard of one ever being used in a fishing competition in New Zealand.

Four main questions were asked of him during the test which was repeated three times. He was asked whether he was the contestant who caught the Marlin, if they were fishing within the tournament boundary and whether he or any other person had tampered with the marlin causing the weight to exceed the eligibility limit set by organisers.

However Mr Young said his crew did everything by the book including keeping the Marlin in a chiller for three days after it was weighed for it to be examined. However no one from OddsOn Promotions came to assess the fish.

The club's weigh master examined the rod and reel, and measured and recorded lengths of ropes, gaffs and lures used to catch the fish, and the scales used to weigh it were all callibrated. Mr Young also has footage from a Go-Pro video of him pulling in the fish and the GPS coordinates from the boat's fish finder recording exactly it was caught.

Dean Young with his 136kg marlin for which he is not allowed to claim his prize after failing a lie detector test. Photo/ Annette Hilton

He believed they had all the evidence needed to prove the catch was legitimate and that they adhered to the competition conditions.

Hawke's Bay Sports Fishing Club president Alex Smith said the club had dealt with OddsOn Promotions for a previous competition, so approached Mr Baty for prize insurance for the Mega Fish Competition.

The club paid Mr Baty $6152 for prize insurance in three fish categories, including the Marlin.

Mr Smith said Mr Baty stated that because the club had won top prizes with large fish in the past, it would be hard for him to get insurance cover.

The club's contract with OddsOn Promotions stated a winning angler may need to undergo a polygraph test, which the club agreed to.

Mr Smith said the club followed International Game Fishing Association rules for using an official weigh masters, certified scales, and all the requirements involving lines, rods and reels.

The club backed Mr Young and his crew 100 per cent. The boat's crew were all past club presidents, vice presidents, club captains and weigh masters.

The fishing club had sent Mr Baty the Go-Pro footage, photographs, screen shot of the boat's GPS coordinates, signed affidavits from all the boat's crew and other independent witness statements. The evidence was pretty conclusive and the club would consider court action if necessary, Mr Smith said.

A club member for 30 years, he had never seen an angler required to do a polygraph test.

Mr Young said Mr Baty had now giving the material to expert consultants and suspended payment until the investigation is complete. Mr Baty also wanted to inspect the angler and boat owners' equipment used to catch the marlin.

In a statement, Mr Baty said he had a long standing relationship with the Hawke's Bay Sports Fishing Club, and had paid out tens of thousands of dollars in claims.

For this particular tournament, they included a polygraph clause that the winner had to pass to complete the claim process.

The result of the polygraph test had resulted in a request for further information from the club. The matter was under investigation.

Massey University law professor Chris Gallavin said it was unconscionable to require somebody to consent to a polygraph test and the courts would look for genuine, free and voluntary submission to a polygraph test.

The evidence could be inadmissible if people had been hoodwinked or put under undue pressure to undergo a test.

Prof Gallavin was unaware of any criminal or civil cases in the New Zealand court system where polygraph results had been admitted as evidence.