Blue whales may become regulars in the Hauraki Gulf, as researchers say an uptick in sightings for the second year in a row could represent a change in behaviour for the world's largest animals.

On the last day of the school holidays, guests aboard whale-spotting boats were treated to a sighting of six pygmy blue whales.

With a bumper week of eleven sightings, as Brad Kirner general manager for Auckland Whale And Dolphin Safari told the Herald, "something has definitely changed."

"In the 17 years prior we've had just five sightings." However, with thirty sightings last year followed by another record winter, the sightings suggest that the blue whales may be here to stay.

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Blue whales seen this weekend in the Hauraki Gulf. Photo / Supplied, Auckland Whale & Dolphin Safari
Blue whales seen this weekend in the Hauraki Gulf. Photo / Supplied, Auckland Whale & Dolphin Safari

The species seen are a subspecies called pygmy blue whale. However, in spite of a diminutive name, they grow just up to 30 metres and can weigh up to 99 tons.

"They're the second largest animal on the planet," says Kirner "The only thing bigger than a pygmy blue whale is a northern blue whale [Balaenoptera musculus]."

Researchers tracking the animals suggest they are migrating to the Hauraki gulf via the South Taranaki Bight, with sightings between July and August.

Researchers and whale watchers hope it might represent a regular "blue whale season" for the Gulf.

This week AUT researchers raised concern of the impact of tourism on whale behaviour in nursery grounds near Tonga. "It's a wonderful experience for the tourist, but it does have the potential to disturb what is a really important part of the lifecycle of whales," Prof.
Mark Oram told RNZ. Humpback nursery areas in Tonga could soon be no-go zones for local tour operators.

For now, in New Zealand waters, whale-watch ventures are part of national conservation efforts and bumper blue whale sightings can only help boost interest from tourists.

See There She Blows: The Herald's Guide to Responsible Whale Watching in Tuesday's Travel magazine