The owner of the Oyang 75, a Korean fishing vessel, has been fined more than $10,000 for dumping harmful substances into the sea.
Southern Storm Fishing Ltd was sentenced in Christchurch District Court for failing to notify the Maritime Authority of two discharges.
In August 2011 inspectors discovered a concealed piping arrangement on board the ship which allowed unfiltered bilge effluent, containing oil, to be emptied into the sea when a hidden switch was turned on.
Southern Storm Fishing made a late guilty plea to the charges.
The fine followed another case late last year in which four of the vessel's crew were found guilty of dumping about $1 million worth of quota fish.