Introducing quotas for catching whales that could be bought and sold could reduce the number of the marine mammals killed each year, it was suggested today.

Writing in the journal Nature, academics from the US said a market of quotas that could be traded would allow environmental groups to "purchase whales" to save them and let whalers profit from the animals without killing them.

Christopher Costello and Steven Gaines, of the University of California, Santa Barbara, and Leah R Gerber of Arizona State University, have proposed the method of putting a "price tag" on whales in the face of the ongoing battle over whaling, which continues despite a global ban.

The researchers said that although a global moratorium began in 1986, the number of whales being caught has more than doubled since the early 1990s to almost 2,000 each year.

In 2010, a 10-year "peace plan" drawn up by the International Whaling Commission proposed limited quotas for those countries which continue to hunt the mammals despite the ban.

The plan would have seen Iceland and Norway, which hunt commercially, and Japan, which exploits a loophole allowing it to catch whales under an exemption for "scientific" whaling, agree to catch limits set by the commission and based on scientific advice.

The bid to introduce quotas - which the IWC said would save several thousands of whales - failed, but the US academics said a trading market could benefit whales and whalers.

In their comment piece, they suggested quotas could be allocated, at sustainable levels, to all member nations of the IWC, who would have the choice of using them or retiring them.

The majority of the quotas could be divided between whaling and non-whaling nations based on historical whaling patterns, with the remainder auctioned and the proceeds going to whale conservation.

The scientists said calculations based on market prices and whaling costs put the profit per whale at around 13,000 US dollars (£8,500) for a minke and 85,000 US dollars (£55,000) for an endangered fin whale.

As a result, prices for whale quotas should be within the reach of conservation groups and even some individuals.

The millions of pounds spent by conservation organisations on fighting whaling could be used to "purchase whales" by buying the quota, with the same or better effect.

It could reduce the number of whales caught - possibly even to zero - and suitably compensate whalers, the scientists said.

In a comment piece in Nature, they wrote: "A fervent anti-whaler will be quick to argue that you cannot and should not put a price on the life of a whale; a species should be protected irrespective of its economic value.

"But unless all nations can by convinced or forced to adopt this view, whaling will continue.

"It is precisely because of the lack of a real price tag in the face of different values that anti-whaling operations have had such limited success."

The academics acknowledged that policing a whale quota market would not be simple, but they said: "By placing an appropriate price tag on the life of a whale, a whale conservation market provides an immediate and tangible way to save them."

Chris Butler-Stroud, chief executive of the Whale and Dolphin Conservation Society, warned that quotas were never scientific and were always subject to political wrangling.

"The more countries and companies that have a financial interest in whales and whaling would mean that, just like fisheries, quotas would be subject to being driven up," he said.

"The mining of the world's whale populations in the last two centuries will not suddenly become sustainable because the last collective responsibilities have been thrown out for the freedom of the market."

And he said: "Much opposition to whaling is not about numbers but is down to ethical and welfare considerations.

"There is no humane way to kill a whale at sea and the hunting process can never be an exact exercise, and so for many countries (and most of the public) the move to the concept of property rights and their trade is unacceptable in the conservation and protection of whales and dolphins."

He also said the current moratorium and capital costs kept many countries out of whaling, but countries such as China and South Korea have indicated they would start if quotas were allocated.

"The property rights model would move cetaceans from being under the stewardship of all nations to be the property of whoever has the ability to access them lethally or the money to 'put off their deaths'," he added.