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Three years ago, a team of marine scientists looked at the global problem of overfishing and came to the grim conclusion that by 2048, populations of all the fish that people around the world eat will have collapsed.

Now, some of those same scientists have joined others to compile a new, more hopeful assessment: Overfishing remains a critical problem, but in some parts of the world, conservation efforts appear to be paying off.

The results suggest that broader use of a small kit of management tools could put global fisheries back on a path to sustainability.

“This is a watershed,” says marine ecologist Boris Worm, one of the lead scientists on the new study and leader of the team that came to the more-pessimistic conclusion in 2006. The new study “shows clearly what can be done not only to avoid further fisheries collapse but to actually rebuild fish stocks” and their ecosystems. Moreover, it represents a baseline scientists and managers can use to gauge progress, he says.

There could be policy implications as well. Past studies have triggered intense disagreements between marine ecologists, who tend to view things from a conservation standpoint, and fisheries scientists, who focus on sustainable exploitation.

“The fact that such a diverse group of folks have gotten together will be a signal to policymakers that they should be taking action,” says Rebecca Goldburg, director for marine science at the Pew Environment Group.

The study has its origins in a National Public Radio call-in show, “On Point.” The guests: Dr. Worm and perhaps the leading critic of the 2006 study, University of Washington fisheries scientist Ray Hilborn.

As the program progressed, Worm recalls, the two scientists discovered they were not that far apart on many issues. Over time, they agreed to collaborate on another study that drew on expertise from both camps. In the end, 21 experts from around the world contributed to the new study, which appears in tomorrow’s issue of the journal Science.

The team looked at research covering 10 of the most intensively studied marine ecosystems – which tend to be associated with fisheries in the developed world. The catch compared with the available biomass is declining in five areas. In seven, this “exploitation rate” is at or below what’s needed to ensure a sustainable catch rate for each ecosystem.

Among the fisheries regions making progress: the US Northeast, Iceland, Alaska and California, New Zealand, and southeastern Australia. New Zealand and Alaska in particular have not waited until fish start disappearing before adopting measures to ensure sustainable catches.

The team identifies a range of tools managers can use, including catch quotas, ocean zoning, setting up no-catch zones in key breeding grounds, and changes in fishing gear.

Even in poor countries, small changes can have a large effect, notes Tim McClanahan, with the Wildlife Conservation Society in Kenya.

Fisherman there realized their nets were catching too many small fish, along with the large ones they prized. By shifting to nets with mesh large enough to let the smaller fish escape, and by closing some areas to fishing, they found that over time, they were catching more large fish. The small fry finally had a chance to grow up.

Still, Mr. McClanahan, says, developing countries face significant challenges in trying to manager their fisheries. Fleets from industrial countries buy fishing rights from developing-country governments and in effect clear-cut the undersea forest.

No one underestimates the political challenges that these measures present. To keep harvests low enough to put stocks on a path to recovery, then to ensure that a fishery is economically as well as ecologically sustainable, means economic hardship in the short run for many people who make their livelihood from the day’s catch.

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