These two kayakers got more than they bargained for on a trip to spot sea turtles off the Hawaiian island of Maui - winding up in the path of an anxious female humpback whale, surging out of the water to protect her young.

The female adult flapped her fin at the passers-by to warn them off, before coming up out of the water as the kayakers quickly escaped. Neither was hurt.

Humpback whales are not aggressive, but adults can reach up to 16 metres in length and 36,000 kilos in weight.

About 60 per cent of the population of North Pacific humpback whales migrates to Hawaii every winter to mate and to give birth to calves conceived during last year's breeding season.

What makes the waters so welcoming is their relatively shallow depth. The maximum diving depth of a humpback is about 180 metres, and the plateau linking the Hawaiian islands doesn't get any deeper than that.

Researchers believe that the population has been rising at a rate of about 7 per cent per year for some time. Just two weeks ago, Maui’s annual Great Whale Count logged a record number of sightings. 150 participants counted 1,726 whales in a three-hour period, almost 400 more than the previous year.

Humpback whales have been internationally protected since the 1960s and shielded under United States federal law. Boat drivers are required to follow an "approach rule" forcing them to travel below 13 knots and to stay 100 yards away from the whales.

"Obviously this can't be helped if the whale comes up beneath or next to you," said Dr Quincy Gibson, Research Director at Pacific Whale Foundation, Maui's oldest and largest marine conservation organisation.

"We are not at the peak of the season yet. There will be a lot more whales here before the winter is over," said Dr Gibson. "We want to remind ocean users to operate with utmost care and at slow speeds in areas where whales are present."

Just a few thousand miles away, the future of many humpbacks hangs in the balance as Japan temporarily halts its controversial "scientific whaling" at the request of the International Whaling Commission.

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