Efforts have been made to protect Guam's coral reef habitats from pollution, eroded silt and overfishing, problems that have led to decreased fish populations. This has both ecological and economic value, as Guam is a significant vacation spot for scuba divers. In recent years, the Department of Agriculture, Division of Aquatic and Wildlife Resources has established several new marine preserves where fish populations are monitored by biologists. These are located at Pati Point, Piti Bomb Holes, Sasa Bay, Achang Reef Flat, and Tumon Bay. Before adopting U.S. Environmental Protection Agency standards, portions of Tumon Bay were dredged by the hotel chains to provide a better experience for hotel guests. Tumon Bay has since been made into a preserve. A federal Guam National Wildlife Refuge in northern Guam protects the decimated sea turtle population in addition to a small colony of Mariana fruit bats.