A new study has revealed shipping noise in the Hauraki Gulf is causing major communication problems for some whales and fish.
The University of Auckland study used recordings from microphones suspended above the sea floor over nine months.
It found noise from ships overlapped 20 percent of vocalisations from fish and whales.
"Every time a vessel passed within 10km of a listening station, it reduced communication space for bigeyes [fish] by up to 61.5 percent and by up to 87.4 percent for Bryde's whales.
"Research has shown bigeyes can communicate over distances of up to 31m, so a passing ship will reduce this to less than 12m."
Associate professor and study author Craig Radford said that drop in communication space was a significant concern.
"The bigeye fish ... use sound to maintain their school structure, which then enables them to optimise their foraging behaviour.
"Whales use it to communicate between males and females ... so a lot of animals now have shown that sound plays a key role in a lot of different life stages."
Mr Radford said the worst affected area was at Jellicoe Channel, which is the most regularly used shipping lane into the ports of Auckland.
But he said a voluntary 10 knot speed restriction by ships within the Hauraki Gulf Marine Park area had a positive impact on underwater noise levels.
"When the ship's doing 10 knots the communication space ... is bigger than what it was previously.
"This is an unknown side-effect that has occurred from reducing the shipping speed in the Gulf to reduce whale strike."
Forest and Bird marine spokesman Anton van Helden said while it was great the speed reduction was having an impact, the Hauraki Gulf was still a noisy place for fish and marine animals.
"Very large noises can create immediate detrimental effects to animals by causing deafness and injury, but these persistent noises in the environment are cumulative.
"So there's lots of noise sources and new sources of noise going in all the time and the animals are having to deal with it."
The study focused on commercial shipping but notes that more than 130,000 recreational boats also use the Hauraki Gulf, with that number expected to rise 40 percent in the next 20 years.
The University of Auckland will be carrying out further research to see what impact that has on fish and marine mammal communication.