Droplet digital PCR data for environmental DNA surveys of Boa imperator in St. Croix, U.S. Virgin Islands, December 2023 and July 2024

Invasive Central American boas (Boa imperator) have established a reproducing population on the western side of St. Croix, U.S. Virgin Islands, as shown by increasing physical capture rates. However, their prevalence throughout the island is largely unknown. The large snakes threaten endemic and endangered species through competition and predation, jeopardizing island biodiversity. Environmental DNA (eDNA) was used as a detection tool to investigate occurrence and focal areas for management efforts in the Salt River Bay National Historical Park and Ecological Preserve (SARI). We collected tissue samples and 13 × 60 mL water samples from a captive boa enclosure on St. Croix to validate a previously developed assay. Then we completed a pilot and main sampling effort. The pilot event, conducted in December 2023, resulted in the collection of 7 × 60 mL water samples per site from SARI (5 sites) and in established areas within western forests (1 site). The main sampling event in July 2024 collected 15 × 60 mL water samples per site within SARI (11 sites) and western forests (4 sites). Samples were filtered individually and consolidated in groups resulting in seven replicates for the pilot and five replicates for the main event for each site, totaling 118 environmental samples. eDNA was isolated using a modified phenol-chloroform isolation method to remove PCR inhibitors, and target eDNA was amplified using droplet digital PCR technology. Water samples from the captive boa amplified target eDNA in 12 of 13 samples. Low concentrations of eDNA (below the 95% limit of detection) were amplified in 4 of 5 sites in established areas and in 8 of 14 sites within the National Park.