Research has shown 14 endangered Bryde's whales found dead in Auckland's Hauraki Gulf in recent years were killed by boats.
An autopsy on a 12-metre Bryde's whale found dead on Friday revealed massive injuries along half its body, said Massey University veterinary pathologist Stuart Hunter.
"It was clear that the whale had severe trauma, running all the way from the rib cage to near the tail of the whale, so it was most likely to be a large vessel that caused these lethal injuries," he said.
One of New Zealand's most endangered species, Bryde's whales are found in the Hauraki Gulf all year round, with ship strike posing the greatest threat to their life.
Auckland University marine scientist Rochelle Constantine has started tagging the creatures to investigate why they are so vulnerable, and found most swim quite close to the surface.
"We have deployed five tags so far and preliminary analysis shows that the whales are spending the majority of their time less than 10 metres below the surface," Dr Constantine said.
"This puts them within the strike depth of many vessels using the gulf."
The researcher urged captains of large ships to be more vigilant in watching out for the huge mammals.
"All vessels using the Hauraki Gulf pose a threat to whales so it is important that everyone using these waters is watching out for these large residents in Auckland's backyard," she said.