The salmon in your sushi may not be what you think it is. (Getty Images)

Researchers have uncovered that salmon products in Washington are frequently mislabeled as wild when they are actually farmed. This mislabeling is particularly costly for customers at sushi restaurants.

The issue of seafood mislabeling has been recognized for some time, prompting Washington state to pass a law in 2013 aimed at reducing fish fraud. Tracie Delgado, a biology professor at Seattle Pacific University, decided to investigate whether the situation had improved since the law's enactment.

"We had no idea what the results would be when we started this project and we were very surprised with the results," Delgado told Gizmodo. "Despite legislation in Washington state that makes mislabeling of salmon illegal, salmon mislabeling fraud is still a problem in Seattle."

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Delgado and her students analyzed the DNA of salmon samples from 67 grocery stores and 52 sushi restaurants in Seattle between fall 2022 and fall 2023. They found that 18% of these samples were mislabeled. The findings were published in the journal PLOS-One.

Mislabeling was more prevalent in restaurants than in grocery stores. About a third of restaurant samples were incorrectly labeled as wild salmon instead of farmed, compared to none in grocery stores. Additionally, some sushi samples marketed as one species of wild salmon were actually another species, a problem also found in grocery stores. The combined rate of mislabeling was 38% in restaurants and 11% in stores.

There's good news, no instances of farmed salmon being mislabeled as wild were found in grocery stores, suggesting that seafood identification laws in Washington have had some impact. However, the overall rate of salmon mislabeling in this study aligns with past estimates before the 2013 law, while other states have reported even higher rates. The costs of mislabeling at sushi restaurants are likely passed down to customers, who may pay more for "wild" salmon that is actually cheaper farmed salmon. This effect was not significant in grocery stores.

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Salmon mislabeling also has environmental implications. "Dishonest reporting of catch data and mislabeling of seafood complicates fisheries' conservation efforts because it prevents accurate tracking of supply chains and complicates effective fishery management efforts," Delgado said. "Therefore, fisheries managers may erroneously conclude that wild salmon stocks which are actually depleted are persisting at sustainably harvestable densities."

The researchers suggest more needs to be done to combat seafood fraud, such as encouraging restaurants to periodically test their fish. The National Oceanic and Atmospheric Administration has an inspection program for fishing boats, processing plants, and retailers, but participation is voluntary. Sushi customers can also take steps to reduce their chances of being defrauded.

"Customers can ask sushi restaurants if they have a quality control process that confirms salmon identification and if they have reliable vendors the sushi restaurant sources from," Delgado said. "Customers can also ask the sushi restaurants if they purchase the salmon whole and then fillet the salmon at the restaurant," or if the sourced salmon is already processed. "If the salmon is filleted fresh at the restaurant, then a good sushi chef would know the difference between a wild vs farmed salmon by looking at it," she explained.