Advances in techniques used to identify sharks and rays have not prevented trade and increase in extinction risk

An analysis of scientific papers published in a 15-year period on molecular methods to identify elasmobranch species shows that better detection of illegal trade has not enhanced protection.

By André Julião  |  Agência FAPESP – The most advanced molecular techniques contribute significantly to the identification of endangered sharks, rays and skates, collectively known as elasmobranchs, and are therefore fundamental to the enforcement of the laws and regulations governing trade in fins and meat from these animals.

An article published in the journal Biological Conservation reports a study by Brazilian scientists showing that 15 years of research on these techniques have not reduced the extent to which the species concerned are threatened.

In fact, some elasmobranch species are more endangered than before: 83% of the 64 species detected in trade are considered at risk of extinction, and the degree of risk has increased for 33 of these in the last 15 years, according to the extinction risk categories used in the Red List of Threatened Species maintained by the International Union for Conservation of Nature (IUCN). The Red List is widely considered a critical indicator of the health of the world’s biodiversity.  

“Trade in endangered elasmobranch species is banned in Brazil, but their meat is sold as ‘cação’ or under other names by grocers, street markets and fishmongers, so consumers don’t know exactly what they’re buying,” said Marcela Alvarenga, first author of the article. She is a PhD candidate at the University of Porto in Portugal and a researcher with the National Center for Molecular Identification of Fish at the Federal University of Rio de Janeiro (CENIMP-UFRJ) in Brazil.

In most cases, it is impossible to identify the species on sale in stores as fillets or cutlets. When the animal is displayed in its entirety, the head and fins are usually missing, and these are necessary to determine the species morphologically. The most accurate identification method therefore entails DNA sequencing to identify one or more genes.

“DNA sequencing is expensive. Even if you have the equipment and trained staff, the reagents are mostly imported, so more cost-effective techniques have been developed in recent years. They can identify degraded DNA in fins that have been left to dry in the sun for days before being exported to Asia, for example,” said Rodrigo Domingues, a co-author of the article. He is a researcher at the University of São Paulo Oceanographic Institute (IO-USP) and principal investigator for a project supported by FAPESP under the aegis of its Research Program on Biodiversity Characterization, Conservation, Restoration and Sustainable Use (BIOTA-FAPESP).

Domingues referred to the international trade in shark fins, whose high value, especially in China, has made sharks targets for predatory fishing vessels. Because the fins must be attached to their bodies at offloading, there is an abundant supply of shark meat, which is nevertheless fetching steadily higher prices. Brazil also imports shark meat from other countries.

The law requires that sharks be landed whole in Brazil, which was one of the first countries to outlaw finning, the gruesome practice of cutting off a live shark’s fins and throwing the rest of the animal back into the sea, where it dies a slow and painful death.

Unlike other ray species, the guitarfish, of which there are three genera, sell for high prices. One species, Pseudobatos horkelii, is listed by IUCN as Critically Endangered. Even shark meat may cost more than other fish in some of Rio de Janeiro’s fish markets, for example.

Fish on sale in a Rio de Janeiro street market. “Viola”, displayed on two signs, is one of the terms used to designate rays, partly due to the Portuguese-language name for Brazilian guitarfish, Pseudobatos horkelii (raia-viola), a Critically Endangered species according to IUCN. Elasmobranchs may also be mislabeled “cação” or as more valuable fish species (photo: Marcela Alvarenga)

Overfishing of sharks and rays is made worse by the fact that they are often entangled as bycatch in the nets of fishing expeditions that set out to catch more valuable species (more at: agencia.fapesp.br/31208).

Techniques advance, protection retreats

The authors analyzed 35 peer-reviewed articles on the subject published between January 2008 and June 2023. Until 2014, most of the articles discussed the development of molecular tools for more cost-effective and rapid identification of elasmobranch species. As of 2018, the predominant techniques were DNA-based sequencing tools directly applied to sharks and rays. In these papers, species were identified from traded body parts and fins seized by law enforcement agents.

These advances were not reflected in a reduction in the degree of extinction risk. In fact, the only such species was the Brazilian cownose ray (Rhinoptera brasiliensis), which IUCN downgraded from Endangered to Vulnerable, whereas 33 of the 64 species mentioned in the papers were upgraded, including 17 species not previously classified as threatened, and seven species whose extinction risk worsened by more than one category.

Fourteen species previously classified as Data Deficient had their extinction risk assessed, including two of the most traded species on the Brazilian coast: the Brazilian sharpnose shark (Rhizoprionodon lalandii) and the Caribbean sharpnose shark (R. porosus), both now classified as Vulnerable.

“Sharpnose sharks reproduce faster than other elasmobranchs, and we thought they weren’t as badly threatened as other shark species. Previous studies warned they were being overfished and could be considered endangered, but unfortunately the warnings weren’t heeded and we’re now seeing the result,” Alvarenga said.

“Our study very clearly shows the importance of using these molecular techniques to monitor the catch and bycatch with a view to law enforcement. Unfortunately, however, this kind of research is patchy, with a PhD dissertation there or a master’s thesis here, whereas it should be systematic,” Domingues said.

The good news is that when law enforcement inspections are strictly conducted, as in the case of federal oversight of the fish processing industry, species substitution and fraud are less frequent, according to another co-author of the article, Antonio Solé-Cava, who heads CEMIMP-UFRJ.

“This can be seen from the fish sold by supermarkets, which are checked by the Department of Animal Product Inspection [DIPOA, an arm of the Ministry of Agriculture, Livestock and Supply (MAPA)], as opposed to street markets, fishmongers and restaurants, which aren’t. In supermarket fish, there’s no substitution or fraud at all. Both are very common in the rest,” said Solé-Cava, referring to a study published by his group.

Besides availability of fish, marine biodiversity is also threatened by reduction and extinction of sharks and rays. As apex predators and mesopredators (midranking predators in marine food webs), they help regulate the ecosystem, removing weak or sick individuals (contributing to selection of the fittest) and controlling populations of several species, among other ecosystem services.

Because of their position in the trophic chain, they absorb large amounts of mercury, making their consumption hazardous. Constant monitoring can help scientists understand the degree to which species are threatened, contributing to assessment of market trends in these products and adjustment of the legislation to conserve fish species and protect human health by warning people not to consume certain species.

The article “Fifteen years of elasmobranch trade unveiled by DNA tools: Lessons for enhanced monitoring and conservation actions” is at: www.sciencedirect.com/science/article/abs/pii/S0006320724001046.