Commercial fishing would be banned from the inner Hauraki gulf and the entire Marlborough Sounds if National creates new recreational fishing parks for those areas.
Prime Minister John Key announced the creation of the new parks while at Westhaven Marina in Auckland this afternoon.
The parks, which will be a new concept created by a reform of current legislation, will cover the inner Hauraki Gulf and the entire Marlborough Sounds.
Mr Key said compensation would likely be paid to affected commercial fishers, which could cost up to $20 million.
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He denied the move was a bid to get fishers on side after a controversial change in bag limits.
The proposed Hauraki park would cover the inner gulf and Omaha Bay and exclude all commercial activity.
The Marlborough Sounds park would also exclude fin-fishing.
If re-elected, National will publish a discussion paper in November.
Further work would be needed to understand how the commercial fishing bans might impact numbers elsewhere.
Conservation spokesman Dr Nick Smith said he would expect any impact to be minimal.
"This is a first for New Zealand ... these areas will be reserved predominantly for recreational fishing and will enhance the opportunity for Kiwi families to catch fish."