2025 Midwest Fish & Wildlife Conference

AUTHORS: Sasha Tetzlaff, US Army ERDC-CERL; Aron Katz, US Army ERDC-CERL; Mark Johnson, US Army ERDC-CERL; Jinelle Sperry, US Army ERDC-CERL

ABSTRACT: Detecting environmental DNA (eDNA) of numerous organisms from the same samples has been revolutionized by metabarcoding. However, utilizing the vast amounts of data generated from metabarcoding to predict occupancy probabilities for co-occurring salmonids and their parasites is currently rare. Using established vertebrate and invert metabarcoding assays on replicate stream water samples collected on Fort McCoy, Wisconsin, we assessed ecological correlates of occurrence for eDNA of native brook trout (Salvelinus fontinalis), its major ectoparasite (gill lice, Salmincola edwardsii), and non-native brown trout (Salmo trutta). Gill lice DNA occupancy was positively associated with brook trout biomass determined via electrofishing conducted near eDNA sampling sites, suggesting gill lice occupancy is dependent on host density. Leveraging site-specific molecular operational taxonomic units identified from metabarcoding, DNA occupancy of trout and gill lice was often positively predicted by species richness of aquatic insect orders trout commonly feed on, which are also environmental quality indicators. Thus, high-quality habitats that environmentally sensitive salmonids and their primary prey rely on may promote higher fish occupancy rates, further facilitating the spread of fish parasites. We suggest our methodological framework could be broadly implemented to enhance understanding of factors impacting distributions of co-occurring salmonids and their parasites to support management and conservation efforts.