Although the policy has attracted scant attention outside the community of those who fish in America and the officials who regulate them, it marks an important shift in a pursuit that has helped define the country since its founding.

Unlike most recent environmental policy debates, which have divided neatly along party lines, this one is about a policy that was forged under President George W. Bush and finalized with President Barack Obama's backing.

"It's something that's arguably first in the world," said Eric Schwaab, the National Oceanic and Atmospheric Administration's assistant administrator for fisheries. "It's a huge accomplishment for the country."

Five years ago, Bush signed a reauthorization of the Magnuson-Stevens Act, which dates to the mid-1970s and governs all fishing in U.S. waters. A bipartisan coalition of lawmakers joined environmental groups, some fishing interests and scientists to insert language in the law requiring each fishery to have annual catch limits in place by the end of 2011 to end overfishing.

Although NOAA didn't meet the law's Dec. 31 deadline -- it has finalized 40 of the 46 fishery management plans that cover all federally managed stocks -- officials said they are confident that they will have annual catch limits in place by the time the 2012 fishing year begins for all species. (The timing varies depending on the fish, with some seasons starting May 1 or later.) Some fish, such as mahi-mahi and the prize game fish wahoo in the southeast Atlantic, will have catch limits for the first time.

Until recently, the nation's regional management councils, which write the rules for the 528 fish stocks under the federal government's jurisdiction, regularly flouted scientific advice and authorized more fishing than could be sustained, according to scientists.

Joshua Reichert, managing director of the Pew Environment Group, said the law's ban on overfishing forced fishery managers to impose limits that some commercial and recreational fishermen had resisted for years.

"This simple but enormously powerful provision had eluded lawmakers for years and is probably the most important conservation statute ever enacted into America's fisheries law," Reichert said.

And unlike many environmental regulations, which are written and enforced by Washington officials, the fishing limits were established by regional councils representing a mix of local interests.

"Because the final decisions were left on the local level, you have a higher assurance of success," said James Connaughton, who helped prepare the reauthorization bill while chairing the White House Council on Environmental Quality. "If it had been imposed in Washington, we'd still be stuck in 10 years of litigation."

But the changes have not come without a fight, and an array of critics are seeking to undo them. Some commercial and recreational operators, along with their congressional allies, argue that regulators lack the scientific data to justify the restrictions. And they suggest that the ambitious goals the law prescribes, including a mandate to rebuild any depleted fish stock within a decade, are arbitrary and rigid.

Rep. Frank Pallone, D-N.J., who has sponsored legislation with Rep. Walter Jones, R-N.C., to relax some of the new requirements, said his constituents are increasingly concerned that fishing will be curtailed without sufficient justification. "As more of these limits go into effect, they get more upset," Pallone said in an interview. "I don't think it's fair to put in place a system that's not scientific and rationally based."

Counting all the fish in the sea is an imperfect science to begin with, and even federal officials acknowledge that they lack the data they'd like for most species. Because of budget limitations, NOAA conducts stock assessments of commercial species only every few years, using independent trawl surveys, official landing data, ecological data and interviews with operators, among other sources.

Its data on recreational fishing are even spottier. NOAA has created an expanded dockside survey and will use new methodology to analyze the results, but officials say they have not made wide use of this approach before this year. After an annual catch limit is set for a recreational fishery, managers can adopt several measures, such as limiting the season or the size of fish that can be taken, to prevent fishermen from exceeding the overall threshold.

Steven Gaines, dean of the Bren School of Environmental Science and Management at the University of California at Santa Barbara, said researchers are developing more effective tools to estimate fish populations, by looking at the size of the fish and how fish are faring inside and outside marine reserves. "It's really transforming the opportunity for us to assess where the fisheries are at the moment and take corrective action early on to correct overfishing," he said.

Even when NOAA receives fresh data, the agency often comes under fire for finding a population is doing better or worse than expected.