Scientists from the University of Pretoria's Mammal Research Institute spotted 845 right whales during a seven-day aerial survey of South Africa's south coast last month, 169 or 20 percent more than last year.

"We are very happy we're getting this rate of increase... People are very pessimistic about whales in general. There are more (now) than there have been for 150 years," Peter Best, a scientist with the institute, told Reuters.

Right whales each have a distinctive pattern of wart-like callosities on their heads, by which they are identified.

Found in the southern hemisphere's sub-tropical and sub-Antarctic waters, they faced extinction in the 1930s due to large-scale whaling.

In fact, they were so-named because whalers regarded them as the "right" whale to kill because they moved slowly and obligingly floated to the surface when killed by harpoons.

By the 1930s uncontrolled whaling by American, British and French whalers had reduced the southern right population off South Africa's coast to between 100 and 200.

They have been protected since 1935 and are now believed to number in the thousands. About 3,000 are estimated to be found off South Africa during the calving season.

Its cousin, the northern right whale, has not fared so well and is believed to number only around 300.

The northern right's woes stem from the fact that its annual migration route between the Caribbean and the rich feeding waters off Nova Scotia is also a busy shipping lane. Many die in collisions with ships.