No abstract

1. Elasmobranchs are apex predators that play a crucial role in marine ecosystems by regulating the dynamics of food webs, as well as connecting different trophic levels across habitats.2. The large-scale removal of elasmobranchs impacts the energy transfer in trophic interactions. The pressure of unsustainable fisheries is considerable, as most elasmobranchs have reproductive strategies that render them unable to recover their demographic status after depletion.3. In Brazil, elasmobranchs are broadly commercialized under the generalist common name of 'cação' (namely, shark meat). This allows threatened species to be commercialized and makes the tracking of different species difficult.4. DNA barcoding of the Cytochrome c oxidase subunit 1 (COI) gene was applied to identify the different species sold as 'cação' along the coastline of Brazil. Fiftyseven samples from 33 cities in 15 coastal states of Brazil were purchased and analysed.5. Bioinformatic analyses revealed the presence of 17 species that were sold as 'cação'. Among them, Prionace glauca (blue shark) was the most abundant. Other species, listed as Endangered under the IUCN Red List of Threatened Species, were also uncovered as being in the shark meat trade, such as Sphyrna lewini (scalloped hammerhead), Isurus paucus (longfin mako shark), and Squatina guggenheim (angular angel shark).6. These findings have reinforced the necessity to correctly label the commercialized species. Public actions towards species-specific management plans must be applied, as well as monitoring the supervised allied educational programmes.

Elasmobranchs are threatened and eDNA metabarcoding is a powerful tool that can help efforts to better understand and conserve them. Nevertheless, the inter‐calibration between optimal methodological practices and its implementation in resource‐limited situations is still an issue. Based on promising results from recent studies, the authors applied a cost‐effective protocol with parameters that could be easily replicated by any conservationist. Nonetheless, the results with fewer elasmobranchs detected than expected reveal that endorsed primers and sampling strategies still require further optimization, especially for applications in resource‐limited conservation programmes.

In order to monitor the effects of anthropogenic pressures in ecosystems, molecular techniques can be used to characterize species composition. Among molecular markers capable of identifying species, the cytochrome c oxidase I ( COI ) is the most used. However, new possibilities of biodiversity profiling have become possible, in which molecular fragments of medium and short-length can now be analyzed in metabarcoding studies. Here, a survey of fishes from the Saint Peter and Saint Paul Archipelago was barcoded using the COI marker, which allowed the identification of 21 species. This paved the way to further investigate the fish biodiversity of the archipelago, transitioning from barcoding to metabarcoding analysis. As preparatory steps for future metabarcoding studies, the first extensive COI library of fishes listed for these islands was constructed and includes new data generated in this survey as well as previously available data, resulting in a final database with 9,183 sequences from 169 species and 63 families of fish. A new primer specifically designed for those fishes was tested in silico to amplify a region of 262 bp. The new approach should guarantee a reliable surveillance of the archipelago and can be used to generate policies that will enhance the archipelago’s protection.

Human impacts have been eroding marine ecosystems in such a way that biodiversity patterns are changing. Therefore, policies and science-based solutions are indispensable for monitoring threats to the most impacted species. In such effort, the analysis of elasmobranchs' environmental traces via eDNA metabarcoding represent a candidate tool for effective monitoring and conservation that is often advocated to be cost-effective and easily replicated. Here, we tested a realistic approach to monitor future changes through elasmobranchs' metabarcoding with published primers, in which, elasmobranch diversity from the coastal waters of the Fernando de Noronha Archipelago (Brazil) was studied here. We detected a total of three elasmobranch species, namely Hypanus berthalutzae, Ginglymostoma cirratum, and Prionace glauca among numerous other fish species. Even though the technique proved to be a useful tool, some practical constraints were identified, and primarily caused by currently published environmental primers. In order to ensure the broad application of the method, we pointed out feasible adjustments to the problematic parameters based on our survey and other elasmobranch metabarcoding studies. The current drawbacks of the approach need to be considered by managers, conservation actors, and researchers, who are considering this methodology in order to avoid unrealistic promises for the cost incurred.