The development of early monitoring tools to detect aquatic invasive species: eDNA assay development and the case of the armored catfish Hypostomus robinii

Introductions of invasive non-native species (and their subsequent impacts) are recognized as a major threat to native flora and fauna. This is especially true in island ecosystems such as the tropical island of Martinique. In 2018, one such aquatic invasive species, the suckermouth catfish Hypostomusrobinii (Loricariidae), was reported for the first time in two of the islands rivers. H. robinii is a popular freshwater aquarium fish and native to tropical and sub-tropical South America. Since its initial discovery, a growing number of populations have been found, suggesting a larger distribution of this species through Martinique's hydrographic network. Here, we developed a novel survey technique (utilizing environmental DNA) and conducted a widespread survey across the island to assess the distribution of this invasive species. We were able to detect H. robinii in 22% of sites surveyed (18 out of 83) via our eDNA-based assay. The presence of these fish was confirmed using traditional trapping at 14 of these sites. Additionally, we used occupancy modeling to investigate the impact of different environmental covariates on the detection efficiency of the novel assay and the potential impacts of false positives and negatives. We highlight a decrease in the detection probability when water volume filtered increases. That said, the eDNA-based method proves a useful tool for the detection of this invasive fish species and monitoring its spread for management purposes.