There are many species of whales and dolphins found in the Islands Unit of the Monument. Some of these species are year-round residents of the Mariana archipelago, while others are seasonal visitors or merely transit through the area. Three local whale species are protected under the Endangered Species Act: the sperm whale, the humpback whale, and the sei whale. Other cetaceans include: short-finned pilot whales, pygmy killer whales, Bryde’s whales, Cuvier’s beaked whales, melon-headed whales, pygmy sperm whales, dwarf sperm whales, spinner dolphins (Stenella longirostris), bottlenose dolphins, pantropical spotted dolphins, striped dolphins, Risso’s dolphins, and rough-toothed dolphins. All of the marine mammals are protected under the Marine Mammal Protection Act.