Humans have been moving animals and plants around the globe intentionally and unintentionally with consequences of introductions affecting ecosystems and native wildlife populations. In the Caribbean, the Small Indian Mongoose (Urva auropunctata (Hodgson, 1836)) seems ubiquitous. We compiled a regional database of 507 islands, discovering that more than 77.7% of Caribbean landmass is occupied by mongoose. Three quarters of these nations engage in mongoose control programs to protect native reptiles and birds, including Sandy Point National Wildlife Refuge in St. Croix, U.S. Virgin Islands. We evaluated the population structure of the mongoose during a capture, mark, and recapture population study spanning 15 years. Consistent mongoose control to protect nesting sea turtles occurred at the refuge in the last four years of the study. We found a 28% (12.2–50.1%) decrease in mongoose population size at the end of the removal years. We suggest that predator suppression tools can successfully reduce mongoose populations where vulnerable species exist. Assessing invasive predator demography before and during programmatic interventions is an important component of conservation problem-solving for invasive predators, even those that are found across landscapes.