In this photo taken Saturday, April 7, 2012, the seiner Pacific Fisher passes the seiner Pilar Bay as crews pump herring aboard the fishing tender Bainbridge, in Salisbury Sound in Sitka, Alaska. (James Poulson/AP)

The vast majority of the world’s fisheries are declining but could recover if properly managed, according to a paper published Thursday in the journal Science.

The statistical analysis marks the first time researchers have assessed the globe’s roughly 10,000 fishing areas, more than 80 percent of which are unregulated. The group of five American scientists who wrote the paper found that small unmanaged fisheries were in much worse shape than regulated ones. Large unmanaged fisheries, on the other hand, performed roughly as well as their regulated counterparts.

Christopher Costello, the lead author and an economist with the Bren School of Environmental Science and Management at the University of California at Santa Barbara, said “one of the bright spots” for the small fisheries “is even though they’re in bad shape and in decline, they’re not yet collapsed.”

“If we turn things around now, we can recover them in a matter of years, not decades, and that has big implications for conservation and food security,” Costello said in a phone interview.

About 20 percent of the world’s fisheries are monitored regularly and regulated; the vast majority around the world operate without any oversight. According to the new study, 64 percent of these unassessed fishing areas “could provide increased sustainable harvest” if they came under scientific management. That, it said, could boost global fish abundance by 56 percent, which could yield more fish for human consumption.

“When fish populations are healthy, they produce more young,” said co-author Steven Gaines, dean at the Bren School. “It may seem paradoxical, but we can get more fish on our plates by leaving more in the water.”

To determine how unassessed fisheries are faring, the team combined a statistical model based on the catch history of individual species, along with information on how fast a species grows and reproduces.

Boris Worm, a marine biologist at Dalhousie University in Nova Scotia, called the analysis a “landmark study that allows us to assess the global state of fisheries in a much deeper way.”

Worm noted the trajectories of managed and unassessed fisheries began to diverge in 1995, when richer countries began to tackle overfishing within their maritime borders.

“The picture that emerges for the world’s fisheries is quite mixed: Many large fisheries that have scientists working on them, are in reasonable shape. Many of the smaller fisheries that have so far been ‘under the radar,’ are doing poorly,” he said in an e-mail. He added that although this presents a problem for developing countries, “fortunately, these problems are quite solvable, as recent, innovative community-based projects have shown in places like Kenya, Chile or Indonesia.”

University of Washington fisheries scientist Trevor Branch noted that large unassessed fisheries make up 99 percent of the world’s unregulated catch and that they are meeting their targets. The researchers “overstate the magnitude” of the information that is lacking about the unmanaged fishing areas, he said in an e-mail, because the U.N. Food and Agriculture Organization already evaluates the status of 445 fisheries that account for 80 percent of the world’s fish catch.

Ray Hilborn, a co-author who is also a University of Washington fisheries scientist, said in an e-mail that although large unregulated fisheries are meeting their target catches, “the trend appears to be downward and this needs to be reversed.”

Small fisheries do not play a major role in the global economy, Hilborn added, but they may be “locally significant” as a source of food for communities in the developing world.

Michael Arbuckle, a senior fisheries specialist at the World Bank, estimated in a recent interview that 240 million people are employed in fisheries worldwide and that these fisheries account for 16 percent of the world’s protein consumption.

The study suggests that many of the world’s fisheries of tuna, such as central West Pacific skipjack and South Pacific albacore tuna, are in relatively good shape, while many snapper fisheries — in places as disparate as Thailand and Latin America — are doing badly. And most of the world’s shark populations, which are targeted in small-scale fisheries, are depleted.

Costello said the findings confirm the observations researchers have made in the field while examining small-scale fisheries in the developing world. “When you stick your head underwater in those places, you realize the fish are gone.”

The study, which is part of a broader fisheries study issued this week by the consulting firm California Environmental Associates, suggests that a range of management tools could help restore depleted fisheries. These include individual fishing quotas, in which fishing operations own a tradable share of the overall catch, and territorial rights fisheries, where a community owns a fishing area and can limit fishing by outsiders.

Brett Jenks, chief executive of the Arlington County-based conservation group RARE, said in an e-mail the new research shows why a combination of rights-based management and protected areas can yield major benefits. RARE has established 40 sites in Asia and Latin America that combine these strategies: An analysis by the University of the Philippines found fish stocks in 12 fisheries in the Philippines were “growing by 40 percent on average in just one year.”

“This anecdote is a clear way of demonstrating Costello and Gaines’s theory in action; fisheries can be incredibly productive if we just give them a break,” Jenks wrote.

Amanda Leland, vice president for oceans at the advocacy group Environmental Defense Fund, said the United States, New Zealand and other industrialized nations have demonstrated that giving individuals a private financial stake in a fishery, known as “catch shares” in the United States, have helped rebuild fisheries by giving fishermen a financial investment in the health of the fishery.

“The data shows there’s a solution to this problem that can be applied broadly,” Leland said. “It’s a rewards system that works.”