"But in these distinct areas where there is a high level of catch by recreational fishers, it is an option we are prepared to consider."
No decision would be made until public consultation on the fishing parks was concluded, he said.
Mr Key downplayed the likelihood of a strict reporting regime.
He noted that recreational fishers' total take was increasing. But reporting every fish caught would be logistically difficult, he said.
"I don't think at this point there's a plan to say 'tell us exactly how many snapper you've caught on a particular day when you're fishing'."
A voluntary reporting system, however, could work "in theory".
Meddling with recreational fishing is a hugely sensitive area for the Government. The ministry was forced to back down on proposed changes to snapper bag limits in 2013 after a huge public backlash, which led Mr Key to say that New Zealanders cared more about snapper than controversial spying changes which were being considered at the time.
LegaSea spokesman Richard Baker, who represents recreational fishers, said any reporting requirement would be a step towards licensing and would provoke another large backlash. He believed that it would also be unnecessary step, because the National Institute of Water and Atmospheric Research (Niwa) already carried out in-depth modelling of the recreational take.
Dr Smith said some fishing groups had backed the proposal, which would help manage the fishing grounds.
Commercial fisheries are already required to report their catch weights to the ministry, and must install technology which measures their catch.
The sector called for changes to the monitoring of recreational fishers' catch earlier this year.
Seafood New Zealand said in January that "it is time to address accurate reporting on the size of the recreational catch", including charter operators who were "largely unsupervised".