Believed to be a stowaway on a U.S. military transport near the end of World War II, the brown tree snake (Boiga irregularis) was accidentally introduced to Guam, that previously had no native species of snake. It nearly eliminated the native bird population. The problem was exacerbated because the reptile has no natural predators on the island. The brown tree snake, known locally as the kulebla, is native to northern and eastern coasts of Australia, Papua New Guinea, and the Solomon Islands. While slightly venomous, the snake is relatively harmless to human beings. Although some studies have suggested a high density of these serpents on Guam, residents rarely see the nocturnal creatures. The United States Department of Agriculture has trained detector dogs to keep the snakes out of the island's cargo flow. The United States Geological Survey also has dogs capable of detecting snakes in forested environments around the region's islands.

Answer this question, if possible (if impossible, reply "unanswerable"): What has the U.S Department of Agriculture done to help watch for the snakes?
has trained detector dogs to keep the snakes out of the island's cargo flow