Angling and trolling for eDNA: A novel and effective approach for passive eDNA capture in natural waters

The conventional water filtration approach for collecting environmental DNA (eDNA) has critical limitations. The collection of eDNA via passive eDNA samplers (PEDS) has been proposed as an alternative to the water filtration method. Here, we developed a novel and rapid eDNA sampling approach and evaluated the extent to which this method enhances eDNA sampling efficiency. We drove boats along transects across nine large natural lakes and deployed PEDS either by briefly submerging them at each sampling location ("angling") or towing them in the water ("trolling"). One liter of water was also collected at each location and processed via the filtration method. Fish biodiversity was determined by metabarcoding analysis of eDNA extracts. Despite a short total submersion time (42-66 min of "angling") and substantially fewer samples (PEDS: 3-6 samples; filtration: 21-33 samples per lake), PEDS generally detected more fish species in each lake as well as per sample compared with filtration. Detection probabilities for fish species were significantly higher for PEDS compared with the filtration method. PEDS are also superior to the filtration method since sampling requires less equipment, labor, time, and costs. Our innovative sampling strategy is thus effective and could be used for the eDNA biomonitoring of large water systems.