New research from northern Tonga is showing that tourism is disturbing the natural behaviour of Humpback whales.

Photo: DAVID BROOKS / AFP

Humpbacks winter-over in Vava'u to give birth and mate before heading back to summer feeding grounds off Antarctica.

Auckland University of Technology's Mark Oram said Vava'u provides sheltered shallows where mothers and calves can bond and feed without interruption from amorous males looking to mate.

The coastal waters provide perfect conditions for tour operators that promote swimming with the whales.

There are now over 20 such companies and Professor Oram said data obtained by drone shows mothers are diving deeper to avoid boats, often separating themselves from calves.

He said rest times between tour operators are being ignored and the industry needs better oversight.

Professor Oram said they are working on recommendations to improve the situation.

"For example, we have some better data now on those sheltered bays that are preferred locations for mothers to give birth and spend their first few weeks with their calves. We may decide for example to set those up as sanctuary areas."

Mark Oram said these nursery areas would be no-go zones for whale-watch operators.