Passengers aboard a boat in Auckland's Hauraki Gulf were treated to a rare sighting of a little-understood whale on a clear blue day earlier this week.

On Tuesday morning, 40 eager voyagers struck wildlife gold when a pygmy blue whale surfaced next to their tour boat.

Auckland Whale & Dolphin Safari marine research officer Catherine Lea said the boat was abuzz after those on board realised it was only the third time in seven years the almost-daily operation had seen this particular subspecies.

Although sightings of the pygmy blue were very unusual in the Hauraki area, the status of the subspecies' population was still a matter of debate.

"Regular" blue whales were considered endangered but the jury was still out on whether pygmy blue whales were also endangered - the result of significant data gaps, as described by The International Whaling Commission.

But research released this month by Leigh Torres and Dawn Barlow of Oregon State University provided further insight into the lives of these mystical ocean-dwellers.

Read the full article at www.stuff.co.nz