Tickets for next year's NgāiTakoto 90 Mile Beach Snapper Bonanza go on sale to this year's competitors on Monday, and will go on general sale on July 1.
Spokesman John Stewart said the dates had been brought forward several months in fairness to those who missed out this year because the 1000 tickets available sold out in December.
This year's competitors were again being given the first opportunity, in part so they could keep their competitor's number if they wished to do so.
"It wouldn't be fair that some people who have fished the contest for the last 20 years could miss out again if everyone from this year buys tickets for 2021," he said.
"A lot of people have traditionally bought tickets as Christmas gifts, but weren't able to last year because of the early sellout."
Competitors from this year whose emails were on the competition's database had been advised, and notice had also been given on the competition's Facebook page. The organisers were also hoping that competitors would spread the word.
"We had a lot of disgruntled people who missed out this year, and we're doing this to be fair to them," Stewart added.
"If we stuck to the old system some people who have competed for years might never get back in."
It was also unfair on those who missed out that some people bought tickets but didn't turn up, solely to keep their competitors' numbers for a future competition.
And more changes were likely in the future.
"Eventtually we are going to have to stop giving the previous year's competitors this opportunity to jump the queue," Stewart said.
"It worked well when we weren't selling all 1000 tickets, but now that we are, and expect to continue doing so, it cuts too many people out.
"What other event does anyone know of where past competitors have the chance to get in before anyone else?"