Using environmental DNA to identify priority areas for sawfish conservation in Costa Rica, Central America

Environmental DNA (eDNA) analysis is becoming a valuable conservation tool for detecting rare and threatened species in a variety of aquatic environments, but studies in freshwater and estuarine habitats with high levels of suspended sediment are still limited. This study used a large-scale eDNA survey to test for the presence of the Critically Endangered largetooth and smalltooth sawfishes Pristis pristis and P. pectinata in Costa Rica. Specifically, we used species-specific TaqMan quantitative PCR assays to test for the presence of both sawfish species in freshwater, estuarine, and marine habitats through a nationwide survey using standardized field and laboratory protocols developed by the Global Sawfish Search Project (James Cook University, Australia). A total of 558 samples were collected from 18 sites, 93 stations, and 6 geographic regions; 486 samples were used to test for P. pristis , 55 samples were used to test for P. pectinata , and 93 were included as negative controls. P. pristis was detected in 16 samples collected from the northern and north Caribbean regions of Costa Rica; however, there were no detections of P. pectinata . Our eDNA survey provides the first indirect evidence for the presence of P. pristis in fast-flowing freshwater habitats with high levels of suspended sediment in Costa Rica. Based on our findings, the San Juan-Colorado River basin, a natural border between Costa Rica and Nicaragua, is a key region in Central America to guide future conservation efforts for the recovery of P. pristis .