Researchers identify way to prevent sea urchin fraud

Sea urchins are a sought-after delicacy but the price they go for on the market depends on their geographic origin. Almost inevitably, a thriving trade in falsifying their origins to defraud customers has sprung up.

The luxury food – known as uni in Japan which accounts for around 90 per cent of the commercial harvest – has become increasingly popular in recent years thanks to its rich flavour and texture, and can sell for princely sums.

Top brands retail for hundreds of dollars for a couple of hundred grams, reflecting the fact that sea urchins are one of the few remaining seafoods that relies exclusively on hand harvesting and is hard to ship long distances without loss of quality. The edible part of the urchin – its gonads – are increasingly used as an ingredient in sushi.

Sadly, prime sea urchin beds in Japan, the US and other areas have become depleted by over-fishing and the loss of kelp habitats that are essential to yield abundant and high-quality harvests. And with demand across North America, Asia, Australia, and Europe showing no signs of abating, unscrupulous sellers are now mislabelling gonads from less sought-after regions in search of illicit profits.

Researchers in China – another big producer and consumer of sea urchins – have investigated the use of stable isotope ratios to identify the origin of Mesocentrotus nudus urchins harvested from the North Yellow Sea, and conclude that the technique could be used to trace their geographical origins.

The team from the Ocean University of China in Qingdao used five different sampling locations in their study, including one in Xiaoping dao, which has a registered trademark and is famous for its prime sea urchin products.

They looked at the ratios of carbon 13, nitrogen 15 and oxygen 18 in gonad samples and found that they gave inconclusive results as to origin. However, applying the same technique to the spines of the urchins allowed samples from five geographic locations to be differentiated with 93 per cent accuracy.

"Provenance of seafood is a concern for regulators, producers, retailers, and consumers," write the authors in the journal Aquaculture.

While sea urchin gonads are often sold separately from their shells, they note that for local brands, sea urchins are commonly sold in whole-alive or half-shell chilled, which makes identifying geographic origins through spines feasible.

"The findings of this study can add significantly to development of reliable and accurate methods that could be used by regulators, producers, retailers etc. to determine the geographical origin of sea urchins to satisfy certification requirements, and to prevent fraud," they conclude.

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