Fish & Game officers fear non-game birds are being illegally targeted by hunters afer dead seagulls were found floating in the Waihou River in the Hauraki Plains.
The discovery was made by officers keeping tabs on hunters during the opening weekend of the game bird season.
Auckland/Waikato game bird manager David Klee said a foggy start to the day was no excuse.
"Targets must be identified beyond any reasonable doubt. We will take a hard line over any such offending, with no such excuses accepted."
Fish & game officers spoke to more than 150 hunters across the Plains area, seizing shotguns and a large quantity of banned lead shot.