"We can't afford to give everyone a contract. So others [rugby and league] come in and pick out what they think is the cream ... We want to encourage these guys to stay and we do our due diligence. We are watching these guys right down to 14 or 15," Kirwan said.
Transfer fees were in vogue in the amateur days and early on in professionalism, but are not commonly enforced now in an open market.
Auckland Rugby Union high performance manager Ant Strachan said they were a grey area, but had been discussed by some unions.
"They are a bit of a minefield. They do still exist in some respects. A player might entertain thoughts of going to another union within his contract period, but that is generally a loan arrangement."
Strachan confirmed that Tupou, who played for the Blues Under-18s last season, is of interest to the union and franchise but is not contracted.
"We're loath to jump into a school and throw a contract at a guy just yet but he knows we're interested in him," he said.
The departures from the Blues of Gareth Anscombe, Pauliasi Manu and Malakai Fekitoa would not come under any transfer fee scenario. Anscombe and Manu were delisted (an outlawed practice) by the Blues while Fekitoa went south where the Highlanders rolled out the welcome mat. All three are contracted to Auckland for this year's ITM Cup.
?Nullifying the Sharks' kicking game and muscling up in the contact areas are going to be the priorities for Kirwan and the Blues ahead of Friday's clash with the table-topping team at North Shore's QBE Stadium.
"Jake White is obviously a great coach and he knows what he needs to do to win. We have to show a lot of energy and especially sort out their kicking game," Kirwan said.
Lolagi Visinia is likely to fill in at fullback for the Blues for the injured Charles Piutau.