The Auckland-Waikato Fish & Game Region was first to bring in the three-shot rule which requires hunters to plug their shotgun magazines to a maximum of three shots.
Other regions (not including Northland) have also introduced restrictions, while Wellington and Nelson Marlborough are banning magazine extensions.
Fish & Game communications manager Don Rood said the rule is another tool to help reduce pressure on game bird populations and provide more opportunity for other hunters.
"We have to strike a balance between providing hunters with enough ducks every season while conserving populations for following seasons," he said.
"We strive to achieve this with appropriate bag limits and season lengths. The three-shot rule is another tool to help sustainability.
