A new and compelling argument for reducing fish harvests - the profit motive - could persuade world fishers to endure the short-term pain of lower catches for the long-term gain of higher returns for their labor, according to ANU experts in a paper published in the journal Science.

The authors demonstrate that when stocks are allowed to recover, profits take a sharp turn upward.

"It has always been assumed that maximizing fishing profits will lead to stock depletion and possibly even extinction of some commercial species," says co-author Quentin Grafton, research director at the Crawford School of Economics and Government at ANU.

"But our results prove that the highest profits are made when fish numbers are allowed to rise beyond levels traditionally considered optimal.  In other words, bigger stocks mean bigger bucks."

"The simple reason is 'the stock effect': when fish are more plentiful and thus easier to catch, fishers don't have to spend as much on fuel and other costs to fill their nets - profits are higher. The U.N. Food and Agriculture Organization (FAO) deems an estimated 25 per cent of world fish stocks depleted - stocks with strength below levels that produce "maximum sustainable yield." 

According to Grafton and co-authors Dr Tom Kompas at ANU and Professor Ray Hilborn from the University of Washington, if stocks were assessed against the levels that maximize profit, many more fisheries would be considered over-exploited.

Their work also shows that higher costs (such as fuel), lower output prices for fish and smaller discount rates all increase the optimal economic stock size relative to the stock size that maximizes the sustainable yield.

"Conservation promotes both larger fish stocks and higher profits," said Dr Kompas, director of the International and Development Economics Program at the Crawford School. 

"This is a win-win for the world's fisheries and for the global marine environment."

"The debate is no longer whether it is economically advantageous to reduce current harvests - it is - but how fast stocks should be rebuilt.