Beyond Hard Parts: Metabarcoding Advances Dietary Resolution in Threatened Amazonian Elasmobranchs

Elasmobranchs are highly vulnerable and are considered one of the most threatened vertebrates worldwide. Insights into diet can improve conservation measures. The bias of traditional morphological methods towards taxa with distinctive hard parts makes metabarcoding analysis a complementary tool to assess diet composition. Here, we analysed the diet of three threatened elasmobranchs ( Carcharhinus oxyrhynchus , Pristis pristis and Pseudobatus percellens ) from the southern Amazon coastal region using specimens from bycatch with a multimarker metabarcoding approach targeting COXI , 12S rRNA and 16S rRNA. The COXI recovered the greatest variety of OTUs, whereas the 12S rRNA identified the highest number of fish OTUs and the 16S rRNA was less representative. For the analysed individuals, P. percellens exhibited a broad diet spanning shrimp, demersal fish and estuarine species, while P. pristis had only three fish species as prey and C. oxyrhynchus presented four prey OTUs, all associated with fish. Our results revealed clear dietary signals and were consistent with the expected capacity of each marker to recover different chordate and invertebrate groups. The studied stomach contents exhibited a predominantly piscivorous diet for the C. oxyrhynchus and P. pristis samples and a more generalist‐opportunistic diet for the P. percellens samples. Although based on few samples from a single region and limited reference databases, our analysis still provides meaningful dietary insights for these threatened species. Overall, our findings provide additional information on the diet of these endangered elasmobranchs in this biodiversity hotspot and highlight the importance of molecular analyses in dietary studies, improving the resolution of trophic relationships and disentangling the role of elasmobranchs in aquatic ecosystems.