Identifying gaps in regulatory prevention measures for nonindigenous aquatic species in the United States

Nonindigenous aquatic species (NAS) present in trade can become costly invaders once introduced and established in a new environment.Preventing NAS introduction is considered the most effective strategy to avoid potential negative ecological, economic, and human health impacts associated with certain species.The United States government enacts regulatory prevention measures carried out by numerous federal agencies with designated authority over certain species, taxonomic groups, and pathways of introduction.We examined 18 case study species across eight taxonomic groups and eight pathways of introduction using a gap analysis approach to identify current gaps in regulatory prevention that may hinder the United States from achieving a more "ideal state" of management in which no NAS or pathways of introduction are unregulated.We found that outside of pathway regulations for ballast water and biofouling, the majority of amphibian, fish, reptile, crustacean, and mollusk species are subject to little to no regulation aside from a few specific species that are highly regulated.We also found large knowledge gaps surrounding the diversity of species and quantities of individual organisms introduced into the United States through the hitchhiking and cultural release pathways.We highlight that the current regulatory approach in the United States is a "blocklist" approach where a select list of species is disallowed as compared to an "allowlist" (approved list of species allowed only) or "conditional list" (between a "blocklist" and "allowlist") used by Australia and New Zealand.Increased documentation of the diversity and quantities of NAS entering the United States and a better understanding of the contribution of the hitchhiking and cultural release pathways to NAS introductions could help inform regulatory prevention.