A worker unloads a fresh catch of tuna for export to the US and Japan at Muara Baru, Jakarta's fish port on May 26, 2010. (Romeo Gacad/AFP/Getty Images)

The seafood on your dinner plate is starting to look a little fishy.

A new study that examined illegal and unreported marine harvests brought into the United States found that some fish shouldn’t be on U.S. tables. Up to 32 percent of imported wild shrimp, crab, salmon, pollock, tuna and other catch is poached, according to the study.

Scientists are concerned about illegal fishing 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 accounts for up to 31 percent of the world’s catch, but this study is the first to examine how much of it slips past the better-
inspected ports of the United States.

“That was really a surprise to us,” said Tony J. Pitcher, a professor of fisheries at the University of British Columbia and co-
author of the study, published this month in the journal Marine Policy.

“We thought a well-governed country like the U.S., 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.

U.S. inspectors are 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 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 fish — much of it harvested within the country. Tuna, pollock, crab and cod are Americans’ wild-caught favorites.

But fishing vessels and seafood processors rely on a shell game to deliver illegal and unreported catch to U.S. ports. Ships fish at different spots on the high seas often for months at a time, using “transition vessels” to taxi the catch to market while they keep trolling for fish.

Documentation of where the fish is caught is lax, the study found. 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 at the plants with those that were caught legally.

“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 group in Bethesda, Md.

“I’m thinking the implications could be pretty severe,” Bigford said. Americans assume that 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 fish are processed is sometimes puzzling. For example, prawns caught off of Scotland are often sent to China for processing and 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 small amounts in the country.

Scientists sought out information regarding illegal and unreported catches in 30 countries, looking at various species and where they are caught. They then determined the top countries and species, and examined the weight of the catches.

Based on earlier and similar studies, researchers determined that nearly half of wild-caught seafood imports to the United States could be scrutinized as possible illegal catch.

During 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. Katrina Nakamura, an adjunct professor at the University of British Columbia and one of the authors, said that researchers reached out to people in the seafood industry and conservation organizations that track illegal fishing.

“I spent a few solid weeks just myself weeding through the shrimp to try to separate wild and farmed imports,” Nakamura said. “It’s the first time something like this has been done at the product level.”

The seafood industry, which stands to lose money if it loses the public’s trust, frowns on such reports.

“We had many challenges from people who care a lot about scientific rigor all the way through” to assure that their methods were sound, because the topic is so sensitive, Nakamura said. “In that sense, it was a process of true scientific discovery.”