Almost half of fish sold in markets across Ecuador’s highland cities has been identified as shark meat, according to a new genetic study exposing widespread seafood mislabelling and raising fresh concerns for threatened species conservation.

Researchers analysed 97 fresh fish samples purchased between June and September 2023 from markets in Ambato, Cuenca, Ibarra and Quito in the highlands, and from Guayaquil and Manta along the coast. All samples were sold under generic names such as “corvina” – a term commonly used in Ecuador for white-fleshed fish like weakfish or brotula.

Using molecular techniques targeting the nuclear ribosomal ITS2 region – or, in layman’s term the short, highly variable segment of DNA that acts as a “molecular barcode” to identify species of plants, fungi, and animals – scientists screened each sample for shark DNA.

The results were stark, finding that 47.42% of all samples tested positive for shark meat.

Strikingly, every positive sample came from highland cities. None of the samples collected in the coastal cities of Guayaquil or Manta contained shark DNA, suggesting – scientists behind the study suppose – regional differences in seafood substitution patterns.

Four shark species were identified in the mislabeled products: the Endangered pelagic thresher shark (Alopias pelagicus), the Vulnerable silky shark (Carcharhinus falciformis), the Vulnerable smooth hammerhead shark (Sphyrna zygaena), and the Near Threatened blue shark (Prionace glauca).

The study was led by Juan José Guadalupe, an assistant professor at the Universidad San Francisco de Quito in Ecuador. Published this week in Frontiers the team has expressed their concerns over the findings. Not least because several of the species identified are globally threatened while others are subject to fishing restrictions in Ecuador. 

Although Ecuador does not officially recognise a directed shark fishery, a legal loophole allows the sale of sharks caught as bycatch – a mechanism that has facilitated the landing of hundreds of thousands of individuals annually, primarily for the international fin trade.

The findings come against a backdrop of dramatic global declines in shark and ray populations. According to the International Union for Conservation of Nature (IUCN), roughly one-third of assessed elasmobranch species are threatened with extinction, with global abundance having declined by more than 70% since 1970.

Sharks play a critical ecological role as apex and mesopredators, regulating prey populations and stabilising marine food webs. Their decline can trigger cascading effects across coral reefs, seagrass meadows and pelagic ecosystems. Yet, despite their ecological importance – and despite national protections for several species – enforcement gaps and mislabelling continue to undermine conservation efforts.

Because shark meat is typically sold as skinless fillets, morphological identification is nearly impossible once the animal has been processed. To overcome this, researchers used species-specific PCR amplification of the ITS2 genetic marker – a cost-effective and validated method for detecting shark DNA in market products.

If a sample belonged to a non-shark species, no amplification occurred. Positive samples were identified based on fragment size, allowing assignment to shark families including Carcharhinidae, Sphyrnidae and Alopiidae.

The study was designed as an exploratory survey rather than a nationwide prevalence estimate. However, the high proportion of shark-positive samples in highland cities points to systemic mislabelling rather than isolated substitution events.

Seafood fraud is not only a conservation issue but also a consumer rights concern. Fish in the surveyed markets were typically sold unpackaged and without species-specific labelling, reflecting common purchasing conditions in Ecuador’s traditional markets.

Selling threatened shark species under generic fish names obscures supply chains, weakens fisheries management, and prevents consumers from making informed choices. It may also facilitate the continued exploitation of species protected under national regulations and international agreements.

As a result of the findings, the researchers are calling for the implementation of a national food traceability system, routine genetic monitoring of market products, the stronger enforcement of existing shark protections, and public education campaigns on seafood transparency.

As global shark populations continue to decline, what appears on a market stall may represent far more than a substitution but another link in the chain of overexploitation.

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