Whale populations may have been 10 times larger than suspected before commercial fishing began, genetic studies have found - frustrating nations hoping to lift a 17-year ban on hunting the large marine mammals.

A study led by Professor Stephen Palumbi of Stanford University in California used population genetics to estimate the true size of whale populations prior to intensive fishing in the 19th century. The results are published today in the journal, Science.

The findings could radically change the point at which whaling can recommence under existing International Whaling Commission regulations. Currently, the commission - the London-based body which regulates international whaling - allows for the resumption of whaling when populations reach a little more than half of their historic numbers.

But historical estimates are based on unreliable whaling records kept by ships and dating back to the mid 19th century, said Palumbi: "Whaling logbooks provide clues but may be incomplete, intentionally under-reported or fail to consider hunting loss."

So what was the size of the whale populations before whaling began? Until now, it had been impossible to estimate, because no records existed that could be used - even if they were reliable. So Palumbi and Joseph Roman, a graduate student at the department of evolutionary biology at Harvard University in Boston, turned to genetics.

"The genetics of populations has within it information about the past," Palumbi said. "If you can read the amount of genetic information - the difference in DNA from one individual whale to another - and calibrate that, then you can estimate the historic size of the population."

Small populations tend to weed out all of its genetic differences through inbreeding - not so a large ones, he said: "A large population by contrast should have a lot more genetic variation. Our study shows that humpback whales today actually have about 10 times more genetic variation than would be expected from the whaling logbook estimates. That tells us that, sometime in the past, the population of humpbacks was pretty big."

In their study, the duo analysed three species of whales: humpback, fin and minke. These were decimated in the mid 19th and early 20th centuries by large-scale hunting, driven by a demand for whale products for candles, soaps, whips, corsets and meat.

To simplify the task they studied only whales in the North Atlantic. They found that there were once probably around 240,000 whales in the North Atlantic - about 10 times the previously estimated high of 20,000 based on whaling records.

The worldwide humpback population could have been as high as 1.5 million - or more than 10 times the International Whaling Commission's global historical estimate of 100,000. The figures means that under the commission's rules, it may be a long time before commercial whaling can recommence.

The commission, which represents commercial whaling groups, has as its main goal the recommencement of whaling as soon as whale populations are back to safe levels, said Palumbi.

In 1986, the commission declared a worldwide moratorium on commercial whaling, observed by all 51 member nations - except Norway and Japan, which have broken with the organisation. Under its rules, a majority of members could lift the moratorium and allow other countries to hunt whales in regions where the population has reached 54% of its original population.

Several countries would like to restart commercial whaling; the new research suggests when populations may be large enough to allow whaling to resume.

"We know for example there are about 10,000 humpback whales in the North Atlantic," said Palumbi. "If, as the whaling records suggest, there were about 20,000 before whaling began, then the [commission] could allow whaling sometime in the next decade.

"But if the historical population was really 240,000 as the genetic studies suggest, then we wouldn't be able to start whaling for another 70 to 100 years," he added.

As an alternative to promoting commercial whaling interests, the whaling body could work towards the development of commercial whale watching - an industry that generates more than US$1 billion worldwide, according to a June 2003 report by the conservation group, World Wide Fund for Nature.