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Fish stocks across the world are declining faster than feared, with the smallest fisheries faring worst, a comprehensive study shows – but there is still time to turn the situation around.

More than half of fisheries worldwide face shrinking stocks, with most of these in worse condition than previously thought, leading to yearly economic losses of $50bn.

This more worrying picture emerged from the most wide-ranging and detailed analysis to date, led by scientists at the University of California Santa Barbara and published online by the journal Science. It applied stock patterns from the few hundred big fisheries for which abundant data are available to analyse thousands of fisheries which have never been formally assessed and about which much less is known.

Prior studies produced skewed results by omitting these ‘data-poor’ or ‘unassessed’ fisheries – which account for 80 per cent of the global catch – and only focusing on the few hundred largest, ‘data-rich’ stocks.

These earlier investigations tended to overestimate the global fish population since the most severe decline is found at smaller fisheries, where management is generally less scrupulous.

The latest study showed that data-poor fisheries operate with an average of 64 per cent of the fish required to yield the largest sustainable catch, much less than data-rich fisheries where the average fish population was 94 per cent of this optimum.

Research also found that among unassessed fisheries, the smaller operations were generally in worse condition than their larger counterparts, regardless of region.

The biggest implication of our research is that you can have your fish and eat them too

Professor Christopher Costello

“The impact on food security is most significant for local-level fisheries in poorer countries, but this isn’t just a developing world problem,” said ecologist Sarah Lester. “Small, unassessed fisheries in the US and Europe are often in as bad a shape as those in the developing world.”

Professor Christopher Costello, the study leader, said that if fisheries continue on the current trajectory, their stocks will almost universally continue to decline.

But the investigation also discovered that some fisheries have rebounded under strong management – giving hope that widespread recovery is still possible.

Professor Costello said: “The biggest implication of our research is that you can have your fish and eat them too. There are economic and conservational benefits to be had from better fishery management – you get more fish in the sea and get to harvest more from those stocks.”

Scientists predicted an eventual 40 per cent boost to catches at data-poor fisheries worldwide, and even a doubling for some regions, provided strong management techniques are applied.

Professor Steven Gaines added that better access to stock information, and the ability to forecast the positive effects of stronger management, makes it more likely that fishermen will endure the short-term losses from limiting catch sizes until fishery populations return to optimum levels.

“The good news here is that it’s not too late,” said Prof Costello. “These fisheries can rebound. But the longer we wait, the harder and more costly it will be to bring these fisheries back. In another ten years, the window of opportunity may have closed.”