Lower ship speed limit in Hauraki Gulf reduces whale deaths

Almost 80 per cent of ships in the harbour have dropped their speeds from 14.2 to 10 knots. Photo / Brett Phibbs

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."

On average, two Bryde's whales were killed by ships in the Hauraki Gulf each year, but in the past year only one dead whale had been found.

Mr Tregidga said the challenge now would be for interested groups, including Ports of Auckland, the Department of Conservation and shipping companies, to ensure that decline continues.

"There has been some reluctance in the early stages, and we [the Hauraki Gulf Forum] understand that, but they understood that this was critical to [the whale's] survival and have come on board," he said.

Ports of Auckland Head of Communications Matt Ball said that while news of less whale deaths was encouraging, it could be five years before the 10-knot policy's success could be evaluated.

"Industry bodies have been fantastic about talking to their members about going too fast, but we're not breaking out the champagne just yet."

The current speed limit is voluntary so that ships can travel faster when under time pressure, but Mr Tredidga said a compulsory speed limit could still be enforced.

"It has never been off the table, it's just the least preferred option.

"It's still a possibility but not our practice. The only way we could do [compulsory limits] is through the Resource Management Act."

Ball said shipping industries felt responsible for the welfare of sea animals and hoped they would not be forced to adopt costly mandatory speed limits.