* 63 percent of world fisheries need to be rebuilt
* Catch limits, other restrictions key to recovery
* Climate change, ocean acidification could have impact
WASHINGTON, July 30 (Reuters) - The world's commercial fisheries, pressured by overfishing and threatened with possible collapse by mid-century, could be rebuilt with careful management, researchers reported on Thursday.
In fact, a fisheries expert who in 2006 predicted total global collapse of fish and seafood populations by 2048 is more optimistic of recovery, based on a wide-ranging two-year study by scientists in North and South America, Africa, Australia and New Zealand.
Still, 63 percent of fish stocks worldwide need to be rebuilt, the researchers said.
"I am somewhat more hopeful that we will be in a better state ... than what we originally predicted, simply because I see that we have the management tools that are proven to work," said Boris Worm of Dalhousie University in Halifax, Nova Scotia, Canada. He is a co-author of a paper in the journal Science and also an author of the pessimistic 2006 report.
These tools include: restrictions on gear like nets so that smaller, younger fish can escape; limits on the total allowable catch; closing some areas to fishing; certifying fisheries as sustainable; offering shares of the total allowable catch to each person who fishes in a specified area.
Worm's optimism was provisional, however, because the current research only looked at about one-quarter of the world's marine ecosystems, mostly in the developed world where data is plentiful and management can be monitored and enforced.
Of the 10 major ecosystems they studied, the scientists found five marine areas have cut the average percentage of fish they take, relative to estimates of the total number of fish. Two other ecosystems were never overexploited, leaving three areas overexploited.
HELPING FISHERIES SURVIVE
One key to helping fisheries survive is to revamp a long-used standard called maximum sustainable yield, which means figuring out the highest number of fish that can be caught in an area without hurting the species' ability to reproduce.
The researchers recommended setting fishing limits below the estimated maximum sustainable yield. Maximum sustainable yield should be an absolute upper limit, they said, rather than a target that is frequently exceeded.
Ray Hilborn, a co-author from the University of Washington in Seattle, noted in a telephone briefing that fisheries are also likely to feel pressure from climate change and ocean acidification, which is exacerbated by emissions of the greenhouse gas carbon dioxide.
Hilborn said places with a strong regulations to protect fisheries will probably be in good shape by 2048, but areas that lack this kind of institutional framework could be "quite overfished" by that time.
Tim McClanahan of the Wildlife Conservation Society told reporters that efforts in the developed world to curtail overfishing could mean more overfishing in the developing world, especially in Africa.
The fisheries in the study are: Iceland Shelf, Northeast U.S. Shelf, North Sea, Newfoundland-Labrador Shelf, Celtic-Biscay Shelf, Baltic Sea, Southern Australia Shelf, Eastern Bering Sea, California Current, New Zealand Shelf. (Editing by Doina Chiacu)
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