Even a small increase in dolphin-watching tourism in Auckland's Hauraki Gulf could be detrimental to the common dolphin population, says a Massey University researcher.
Karen Stockin, research officer with the university's coastal-marine research group, said her research since 2002 showed the presence of tour boats caused the marine mammals to spend significantly less time foraging.
She found the time dolphins spent foraging was reduced by about 12 per cent in the presence of a tour boat.
The probability of resting dolphins remaining in rest behaviour after a tour boat visit was also reduced.
Ms Stockin said such impacts associated with foraging were potentially detrimental for the population of common dolphins in the gulf.
"Foraging and resting bouts are significantly disrupted by boat interactions to a level that raises concern regarding the sustainability of this impact."
Ms Stockin said it was also a concern that the common dolphin population moved up to the Bay of Islands, where there were attempts to expand marine mammal tour operations to species other than the bottlenose dolphins in the area.
Tourism impacts identified for common dolphins in the Hauraki Gulf were similar to those previously reported for bottlenose dolphins in the Bay of Islands, she said.
"They are as susceptible if not more susceptible."
Ms Stockin said even a 5 per cent increase in tourism in the gulf could lead to a significant alteration of the overall behaviour of the common dolphin population and jeopardise the sustainability of the industry.
In her doctoral research Ms Stockin observed the impact of the one dolphin-watching operator in the Hauraki Gulf at the time.
"Despite low-level tourism in this region, the use of experienced skippers and full compliance with the marine mammal regulations, significant impacts were still reported for this species."
A second dolphin tour operator had since been granted a permit to take tourists into the gulf for marine mammal watching but its effects were yet to be determined.
William Goodfellow, managing director of Auckland Dolphin and Whale Safari, said the company endorsed Ms Stockin's research.
The company was the first to get a permit to run dolphin and whale watching tourism in the gulf and had operated since 2000.
He said that if tourism activity in the gulf increased by "not too much", there could be cause for concern.