A voluntary lower speed limit through the Hauraki Gulf has helped reduce the number of whale fatalities in the popular shipping route.
The Hauraki Gulf Forum said the voluntary ten-knot speed limit for ships travelling in the Gulf introduced in September 2013 aimed to reduce deaths among the area's semi-resident population of about 50 endangered Bryde's whales.
Almost 80 per cent of ships in the harbour have dropped their speeds from 14.2 to 10 knots.
It's a decrease that Hauraki Gulf Forum Chair John Tregidga said made all the difference to Bryde's whales, which spend most their time within the top ten metres of the water's surface.
"There's an 80 per cent chance that whales struck by ships travelling at 14 knots will be killed, but at ten knots that drops to 25 per cent."