WASHINGTON — That seafood on your dinner plate is starting to look a little fishy.
A new study that examined illegal and unreported marine harvests brought to the United States from around the globe says it maybe shouldn’t be there at all. Up to 32 percent of imported wild shrimp, crab, salmon, pollock, tuna, and other catch was poached.
Illegal fishing is a major concern of scientists because the world’s oceans can barely sustain legal seafood harvests. Eighty-five percent of the world’s commercial seafood grounds ‘‘are fished up to their biological limits or beyond,’’ the study said.
Earlier studies have shown that illegal and underreported fishing comprises up to 31 percent of the world’s catch, but this study is the first to examine how much of it slips through the better-inspected ports of the United States.
‘‘That was really a surprise to us,’’ said Tony Pitcher, a professor of fisheries at the University of British Columbia who helped author the study, ‘‘Estimates of illegal and unreported fish in seafood imports to the USA,’’ published this month in the journal Marine Policy.
‘‘We thought a well-governed country like the US, with tighter controls, would be better,’’ Pitcher said. Inspectors in the United States, which imports 14 percent of the global total, are not required to ask for documentation that shows a bounty’s origin.
US inspectors are far more concerned with the freshness of seafood and its potential impact on human health. What gets by inspectors is valued in the study at $1.3 billion to $2.1 billion per year, a sum that only encourages more illegal and unreported fishing, Pitcher said.
‘‘It’s quite clear that most consumers don’t have an idea what’s coming into the supply,’’ he said. Americans ate about 2 million tons of seafood in 2011, second only to China. They spent more than $85 billion on seafood products — much of it harvested within the country — in stores, restaurants, or elsewhere. Tuna, pollock, crab, and cod are America’s favorite wild-caught seafoods.
But fishing vessels and seafood processors rely on a shell game to deliver illegal and unreported catches to US ports. Ships fish at different spots on the high seas, often for months at a time, using ‘‘transition vessels’’ to taxi their catches to market while they keep trolling for fish.
Documenting where the fish were caught is lax, the study’s authors said. Many of the fish, crab, shrimp, and other products are rushed to Chinese processing plants, where low-paid workers fillet salmon, clean the guts of tuna, and pull meat from crabs. Illegally caught fish are easily mixed with legally caught fish at those plants.
‘‘If so much of the overall harvest is under the radar, what about the by-catch,’’ the marine life caught in nets or on hooks, said Tom Bigford, policy director of the American Fisheries Society, a nonprofit in Bethesda, Md.
‘‘I’m thinking the implications could be pretty severe,’’ Bigford said. Americans assume seafood that makes it into the United States was legally caught, he said. ‘‘But the chain is so complicated that it’s hard for us to be positive.’’
How the world’s fish are processed can boggle the mind. For example, prawns caught off Scotland are often sent to China for processing and are then shipped back to Scotland because low-wage processors are cheaper, Pitcher said.
Pollock caught in Russia is frozen there, shipped to China, where it is thawed and processed, then frozen again for the trip back to Russia or elsewhere in the world, including the United States.
Most wild-caught imports to the United States come from 10 countries: China, Thailand, Indonesia, Ecuador, Canada, Vietnam, the Philippines, India, Mexico, and Chile.
For the study, researchers looked only at fish caught under flags outside the United States, although illegal and unreported fishing does occur in relatively low amounts in the country.
They sought out information regarding illegal and unreported catch in 30 countries, looking at various species and where they are caught. Once they gathered the information, they determined the top countries and species, and examined the weight of the catch.
Based on earlier and similar studies, they determined that nearly half of wild-caught seafood imports to the United States could be scrutinized as possible illegal catch. Over the two years of the study, researchers ‘‘spent months developing the framework,’’ relying on peer reviews to check their steps, checkpoints, and initial findings for scrutiny.