A critically endangered Bryde's whale has washed up dead on Motuihe Island in the Hauraki Gulf.
Project Jonah chief executive Kimberly Muncaster said it was too soon to tell how the whale had died, but conservation staff were investigating whether it had been struck by a ship.
"Unfortunately with this species, they are prone to being hit by ships, particularly in the Hauraki Gulf. We have a resident population that live in the Hauraki Gulf and there have been a number of incidents over the last few years involving ship strike.''
The Department of Conservation (Doc) agreed that ship strike poses the greatest threat to Bryde's whales in the Hauraki Gulf.
Doc staff were securing the animal so a necropsy could be carried out within the next couple of days.
Ms Muncaster said the death of the critically endangered whale was "incredibly sad''.
New Zealand is one of the few places in the world with a resident population of the Bryde's whale. Fewer than 200 frequent the Hauraki Gulf, where their population is centred.
There have been 41 confirmed Bryde's whale deaths in the Hauraki Gulf in the last 16 years. Of the 18 which were examined, 15 were likely to have died from ship strike.
The latest death comes after a Bryde's whale, seen floating in the gulf in February, was found to have been hit by a vessel.
Doc Auckland area biodiversity manager Phil Brown said at the time that he was concerned by the number of Bryde's whales being struck.
He said a lower speed limit for commercial ships passing through the Hauraki Gulf Marine Park could help to protect them.
University of Auckland researchers are currently looking into why Bryde's whales are so vulnerable to ship strike.
Preliminary analysis has found the whales spend most of their time less than 10 metres below the surface, which puts them within the strike depth of many vessels.
Visit www.projectjonah.org.nz to find out more about Project Jonah.