A voucher-based survey of arachnids from salmonid fish (Oncorhynchus spp.) gut contents

This investigation identifies arachnid prey of juvenile salmonid fishes (Oncorhynchus spp.) in a coastal stream in Marin County, California. Using morphological identification and DNA sequencing of the metazoan barcode gene (cytochrome c oxidase subunit I), arachnids recovered from salmon gut lavage samples were identified. The non-invasive specimen-specific sequencing approach allows for an association of the specimen with sequence data, something often lacking in metabarcoding or eDNA studies. To identify potential source habitats, the guilds of the spiders and mites studied were classified. No samples were contaminated, and genus-level identifications were achieved in all spiders, with species-level identifications in 38% of spiders. These findings provide insight into the arachnid prey within aquatic ecosystems, aiding our understanding of allochthonous contributions to freshwater environments and their fish predators. These contributions have implications for ecosystem dynamics, nutrient cycling, contaminant accumulation, and conservation broadly.