Advances in techniques used to identify sharks and rays do not prevent trade or increase risk of extinction: study

The most advanced molecular techniques contribute significantly to the identification of endangered sharks, rays and rays, collectively known as elasmobranchs, and are therefore fundamental to the enforcement of laws and regulations governing the fin and meat trade of these animals.

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

In fact, some elasmobranch species are more threatened than before: 83% of the 64 species detected in commerce are considered at risk of extinction, and the degree of risk has increased for 33 of them over the last 15 years. recent years, depending on the risk of extinction. 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 global biodiversity.

“Trade in endangered elasmobranch species is banned in Brazil, but their meat is sold as “cação” or other names by grocers, street markets and fishmongers, so consumers do not don't know exactly what they're buying,” said Marcela Alvarenga, first author of the article. She holds a Ph.D. candidate at the University of Porto in Portugal and researcher at the National Center for Molecular Identification of Fish of 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 exhibited in its entirety, the head and fins are generally absent, necessary for the morphological determination of the species. The most precise identification method therefore consists of sequencing the DNA to identify one or more genes.

“DNA sequencing is expensive. Even if you have the equipment and trained personnel, the reagents are mostly imported, so more cost-effective techniques have been developed in recent years. They can identify the “DNA degraded in fins that were left to dry in the sun for days before being exported to Asia, for example,” said Rodrigo Domingues, co-author of the paper and researcher at the Oceanographic Institute from the University of São Paulo (IO-USP).

Domingues cited the international trade in shark fins, whose high value, particularly in China, has made sharks targets for predatory fishing vessels. As the fins must be attached to the body during unloading, there is an abundant supply of shark meat, which nevertheless fetches increasingly high prices. Brazil also imports shark meat from other countries.

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

Unlike other species of rays, guitarfish, which come in three genera, command high prices. One species, Pseudobatos horkelii, is classified by the IUCN as critically endangered. Even shark meat can cost more than other fish in some fish markets in Rio de Janeiro, for example.

Overfishing of sharks and rays is made worse by the fact that they are often accidentally caught in the nets of fishing expeditions aiming to catch more valuable species.

Techniques advance, protection retreats

The authors analyzed 35 peer-reviewed articles on the topic, published between January 2008 and June 2023. Until 2014, most articles discussed the development of molecular tools for more cost-effective and rapid identification of species of elasmobranchs.

As of 2018, the predominant techniques have been DNA-based sequencing tools directly applied to sharks and rays. In these documents, species were identified from traded body parts and fins seized by law enforcement agents.

This progress has not translated into a reduction in the degree of extinction risk. In fact, the only such species was the Brazilian cownose skate (Rhinoptera brasiliensis), which the IUCN downgraded from Endangered to Vulnerable, while 33 of the 64 species mentioned in the documents were reclassified, including 17 species not previously classified as threatened, and seven species. whose risk of extinction has increased by more than one category.

Fourteen species previously classified as data deficient have 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 more quickly than other elasmobranchs, and we thought they were not as threatened as other shark species. Previous studies warned that they were overexploited and could be considered endangered of disappearance, but unfortunately the warnings were not heeded and we are now seeing the result,” said Alvarenga.

“Our study shows very clearly the importance of using these molecular techniques to monitor catches and bycatch for law enforcement purposes. Unfortunately, this type of research is spotty, with a doctoral thesis out there or a master's thesis here, when it should be systematic,” Domingues said.

The good news is that when police inspections are strictly conducted, as in the case of federal oversight of the fish processing industry, cash substitution and fraud are less common, according to another co-author of the paper. article, Antonio Solé-Cava, who directs CEMIMP-UFRJ.

“This is seen in the fish sold in supermarkets, which is controlled by the Department of Animal Products Inspection (DIPOA, a branch of the Ministry of Agriculture, Livestock and Supply (MAPA)), as opposed to street markets, fishmongers and restaurants”, which is not the case. In supermarket fish there is no substitution or fraud. Both are very common in the rest,” Solé-Cava said, referring to a study published by his group.

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

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