Boat trips offering passengers a chance to swim with dolphins in the Bay of Islands have been axed amid fears for the future of the local dolphin population.

The number of bottlenose dolphins in the Bay has plummeted from 270 in 1999 to a current estimate of 31, a decrease of almost 90 per cent, the Herald reports. 

The new rules for commercial operators also limit dolphin watching tours to afternoons only and cut the interaction time from 30 minutes per cruise to 20.

In 2016 a Massey University report found the Bay's bottlenose dolphins were ''being loved into extinction'' because the marine mammals were interacting with humans so much they had little time left for feeding, nursing their young or sleeping.

The study also found three-quarters of dolphin calves died before adulthood, the highest mortality rate observed anywhere in the world.

Department of Conservation ranger Cat Peters says this is for the good of the species.

She told Mike Yardley the population hasn't necessarily declined from death and it's possible the species is leaving the area.

"If we can improve the conditions that the dolphins are encountering in the local area, there's every opportunity that they might come back to the Bay of Islands."