Sniffer dogs were used to check predator-free islands off Northland's coast after a boat broke a mooring and drifted onto rocks, sparking a conservation scare.
A 6.5m boat, formerly used as a commercial crayfishing vessel, drifted from Flat Island near Great Barrier Island and beached in Boulder Bay on Whatupuke Island - in the Hen and Chicken Islands.
Department of Conservation ranger Marie Jordan said there were concerns there may have been rats on the boat that might have survived the journey and got onto the island.
The islands are a no-go zone without a department permit.
DoC officials went to the island last Thursday to help the owner, who had tracked down his boat.