Fish and Game says up to 20 compliance orders have been handed out to South Island duckshooters caught hunting illegally.
The duckshooting season started on Saturday morning.
Fish and Game's South Island communications adviser, Andrew Currie, said on Saturday that between 12 and 20 compliance orders had already been given to hunters who did not have licences.
He said some were landowners, but they still needed a licence because they were hunting on neighbouring land.
The hunters' guns were confiscated, along with any birds they had shot; the guns will be returned when they present valid licences to Fish and Game.
Mr Currie says three compliance orders were also issued in the eastern North Island because hunters there had caught too many ducks.
He says Fish and Game has been monitoring bird numbers, and it looks as though there are more mallards now than in the past few years, and the number of paradise shelducks is also healthy.