BATOseq-PE: A public batoid DNA library with the first molecular insights into the cryptic diversity, genetic health, and management of Peruvian marine rays

The ocean floor off the coast of Peru is a bustling, high-pressure marketplace for life, where the cold, nutrient-rich waters of the Humboldt Current support a dense and diverse community of rays. These flat, cartilaginous fish, ranging from the massive manta rays that glide near the surface to the small, bottom-dwelling skates, are vital to the marine ecosystem. Yet, for decades, our understanding of who lives there and how they are related has been clouded by a lack of clear identification. Traditional methods of telling species apart rely on physical features like the shape of a fin or the pattern of spots, but these traits can be misleading, especially when the animals are caught, processed, or when distinct species look nearly identical. To cut through this confusion, scientists have turned to DNA barcoding, a technique that reads a specific, short segment of genetic code found in every living thing. This genetic snippet acts like a unique fingerprint, allowing researchers to identify a species with certainty, even from a small piece of tissue or a processed fillet in a market. Without this molecular clarity, it is impossible to know if a fishery is sustainable, if a population is shrinking, or if a rare species is being caught by mistake.

A team of researchers has now taken a massive step forward in securing the future of these animals by creating the first public, open-access library of genetic codes for Peruvian marine rays. Called BATOseq-PE, this project involved collecting tissue samples from 75 individual rays found in local fishing ports and markets across the country. The team worked with specimens that had already been caught, ensuring no live animals were harmed, and extracted DNA to sequence the genetic barcodes for 14 different species. They also used advanced computer tools to assemble a complete genetic blueprint, known as a mitogenome, for a rare skate called Notoraja martinezi, a species that had never before had its full genetic sequence made public. By adding these new sequences to global databases, the researchers have effectively doubled the amount of public genetic data available for rays in this region, turning a patchwork of private records into a shared resource that anyone can use to identify these animals.

The power of this new library became immediately apparent when the researchers began to look closer at the genetic differences between the animals. They discovered that what was thought to be a single species of ray, the Rostroraja velezi, actually contains two distinct genetic lineages living side by side in the same waters. One group matches the original description of the species, while the other represents a hidden, or cryptic, lineage that has been evolving separately. This finding suggests that the true diversity of rays in Peru is higher than previously recorded, and that some species may be more complex than their physical appearance suggests. Furthermore, the study revealed that for several other species, including the devil rays and eagle rays, the genetic variation within the population is alarmingly low. In some cases, every single individual tested carried the exact same genetic code, a sign that the population has likely suffered a severe decline or a "bottleneck" where only a few survivors remained to rebuild the numbers.

This lack of genetic diversity is a critical warning sign for conservation. The researchers combined their genetic findings with data on how many rays are being caught and where they are found to create a new tool for prioritizing protection. They found that the species under the heaviest fishing pressure are often the same ones showing the lowest genetic health. For example, the Peruvian diamond stingray and the Pacific eagle ray showed almost no genetic variation, indicating that intense fishing has stripped away the unique genetic lineages that help a population survive changes in the environment. The study also highlighted that many species, particularly those found in deep water or those that are rarely caught, have no genetic data at all, leaving them invisible to conservation efforts. By mapping these gaps, the team has identified which species need immediate attention and which require urgent sampling to prevent them from disappearing without anyone knowing they were there.

The implications of this work extend far beyond a list of new genetic codes. The researchers found that the fishing industry in Peru is heavily reliant on a few key groups of rays, and the data shows that these populations are being pushed to their limits. While some species are protected by law, loopholes in regulations allow others to be caught and sold, often without clear identification. The new genetic library provides the scientific foundation needed to close these loopholes, allowing authorities to verify exactly what is being landed and to enforce rules based on accurate species identification. The study also suggests that some rays, like the devil rays, may travel long distances across the ocean, connecting populations in Peru with those in Mexico and Ecuador. This means that protecting these animals requires international cooperation, as a fish caught in one country may belong to a stock that was born in another.

Ultimately, this research transforms how we see the rays of the Eastern South Pacific. It moves the conversation from guessing based on appearance to knowing based on evidence. The creation of the BATOseq-PE library is not just a technical achievement; it is a practical tool for survival. By making these genetic fingerprints public, the researchers have given fisheries managers, conservationists, and scientists the ability to track the health of these populations with precision. The findings paint a picture of a marine ecosystem that is both rich in hidden diversity and fragile under the weight of human activity. The path forward is clear: use the genetic data to guide fishing limits, protect the most vulnerable lineages, and ensure that the unique evolutionary history of these ancient creatures is not erased before it is fully understood.