WASHINGTON - By the end of this year, the world is projected to reach an unheralded but historic milestone: Half of the fish and shellfish we consume will be raised by humans, rather than caught in the wild.
Reaching this tipping point is reshaping everything from our oceans to the livelihoods and diets of people across the globe. It has also prompted a new round of scientific and political scrutiny, as researchers and public officials examine how aquaculture is affecting the world's environment and seafood supply.
"Hunting and gathering has reached its maximum," said Ronald Hardy, who directs the University of Idaho's Aquaculture Research Institute and co-authored a study on the subject in the Proceedings of the National Academy of Sciences. "We've got to grow more."
The drive to bring fish "from egg to plate," as Hardy puts it, has the potential to answer a growing demand for seafood worldwide, as well as reduce some of the imports that compose more than 80 percent of the fish and shellfish Americans eat annually.
But without technological advances to improve efficiency, it could threaten to wipe out the forage fish that lie at the bottom of the ocean's food chain and contaminate parts of the sea.
And consumers will have to accept that they are eating a different kind of fish than the ones that swim wild: ones that might have eaten unused poultry trimmings, been vaccinated, consumed antibiotics or been selected for certain genetic traits.
Although there is still debate about farming's share of the world fish supply - the United Nations' Food and Agriculture Organization estimates it stood at 44.3 percent in 2007, whereas the PNAS study says it will reach over half in a matter of months - no one questions that aquaculture has grown exponentially as the world's wild catch has flattened out. In 1970, farmed fish accounted for only 6.3 percent of global seafood supply.
This trend reflects global urbanization - studies show that as more people move to cities, they are consuming more seafood - but it is changing the world's seascape as well.
Vessels now venture to the Antarctic Ocean to catch the tiny krill that have sustained penguins and seals there for millennia, and slender poles strung with farmed oysters and seaweed jut out of Japan's once-pristine Matsushima Bay.
Nature Conservancy senior scientist Mike Beck said some Chinese bays are so crammed with net pens that they are no longer navigable.
Moreover, fishermen such as Shannon Moore, who catches salmon in Washington state's Puget Sound, worries about how farmed fish's parasites are affecting wild stocks. "These young wild critters are pretty small, and they can ill afford to have these hitchhikers on them," Moore said, referring to parasites that plague juveniles migrating near Canadian fish farms.
But aquaculture's proponents suggest that farming represents the best chance of giving people a chance to make a living off the sea. Sebastian Belle, executive director of the Maine Aquaculture Association, noted that three-quarters of his group's members are either current or former commercial fishermen, and although the average age of Mainers with a fishing lease permit is 57, the average for those with a fish-farm permit is 33. "It's really the next generation of watermen," Belle said.
Jane Lubchenco, who used to write about aquaculture's environmental impacts as an academic before taking the helm of the National Oceanic and Atmospheric Administration, announced this month her agency will come up with a national policy to address fish farming.
"It's important that aquaculture be done in a way that's sustainable," she said in an interview.
The question of how best to develop future fish farms has set off a flurry of activity and experiments, as scientists and entrepreneurs try to resolve the environmental challenges fish farming poses.
The biggest one involves a fundamental quandary: One needs to feed many small fish to bigger fish to produce ones consumers crave.
"We've got to come up with an alternative that breaks the connection between aquaculture and wild fishing of forage fish," said Stanford University professor Rosamond Naylor, the PNAS study's lead author.
China a leader
America now ranks as a minor player in global aquaculture: It accounts for 5 percent of the nation's seafood supply, but the $1.2 billion in annual production is 1.5 percent of the world's total. In 2006, China supplied 62 percent of the world's farmed fish and shellfish, according to the United Nations' Food and Agriculture Organization.