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

Abstract

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 (Pristis pristis) and Smalltooth (P. pectinata) sawfishes in Costa Rica. Specifically, we used species-specific TaqMan quantitative PCR (qPCR) 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 six 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. Pristis 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.