Weak eDNA detection of signal crayfish (Pacifastacus leniusculus) despite no physical specimen capture in Alexandria, MN

Signal crayfish (Pacifastacus leniusculus), a highly invasive species in many parts of the world, were first confirmed in Lake Winona, Minnesota, in fall 2023 after being caught by a local bait harvester. In 2024, we conducted an extensive monitoring effort to assess their presence and potential spread to nearby lakes. Over several months, we deployed multiple trapping methods but did not capture any signal crayfish. In parallel, we collected 142 water samples from Lake Winona and 15 surrounding lakes for environmental DNA (eDNA) analysis. eDNA assays detected very low levels of signal crayfish DNA in four samples: two from Lake Winona (the original detection site), one from Lake Henry, and one from Lake Carlos. Three detections were supported by only a single positive technical replicate and one by two, indicating extremely weak amplification. Taken together, trapping and eDNA results suggest either a very low-density population of signal crayfish or alternative sources of eDNA. This dataset documents the monitoring effort and findings by two datasets: (1) eDNA results and (2) trapping effort and results.