Tracking sharks and rays in continental estuaries of Central America: Using eDNA to inform conservation in the Eastern Tropical Pacific

The Eastern Tropical Pacific (ETP), a highly productive and biodiversity-rich region stretching from Baja California in Mexico to the Gulf of Guayaquil in Ecuador and encompassing islands like the Galápagos, provides vital habitats and migratory corridors for a diverse array of marine megafauna, including threatened and endangered species of sharks and rays. The ETP Marine Corridor (CMAR), a regional collaborative effort between the governments of Colombia, Costa Rica, Ecuador, and Panama, was established in 2004 to protect migratory routes and habitats by linking existing Marine Protected Areas (MPAs) into a cohesive network, expanding existing MPAs and addressing overfishing and illegal fishing. CMAR is a model for transnational conservation efforts, but significant challenges remain in ensuring the long-term protection of elasmobranchs that rely on habitats that remain overfished for part or most of their life cycle. Estuaries and mangrove fringed bays on the coast of Central America are critical breeding and nursery habitats for many shark and ray species, yet remain outside of the CMAR framework and are vulnerable to anthropogenic impacts. Our team is leveraging environmental DNA (eDNA) detections to track seasonal patterns of habitat use by migratory and resident shark and ray species in 16 estuaries of the Pacific of Panama and Costa Rica where traditional censusing methods would be cost-prohibitive and logistically challenging to conduct at that scale. We are using a two-pronged approach to address science gaps and inform policy. First, we are targeting whole elasmobranch assemblages in water and a sediment eDNA time-series to characterize spatial and temporal turnovers and identify key hotspots for elasmobranch diversity. Second, we are using highly sensitive species-specific assays to detect the occurrence of critically endangered elusive species. Results indicate that the distribution of sharks and rays is heterogenous in space, with a few estuaries playing a disproportionately important role in the life histories of multiple species. We detected the presence of the critically endangered largetooth sawfish in an estuary where there are no previous confirmed sightings, highlighting the value of eDNA for rapid assessment of rare and elusive species. Together, our results provide a strong scientific foundation to expand management and protection to key continental coastal habitats within the CMAR framework.