The monument is exceptional for its diversity and abundance of marine mammals, including at least 10 dolphin species, seven large whale species, and six medium whale species. There are several species that are very rare, including the endangered North Atlantic right whale, sperm whale, sei whale, and fin whale. The monument is also home to three species of beaked whales, which are known to be some of the best divers on the planet, with a recorded maximum dive depth of almost two miles (9,000 feet) in the submarine canyons!
During aerial surveys, researchers have observed several marine mammals feeding, some accompanied by calves, indicating that this area is likely important as feeding and nursery habitat for many species of whales and dolphins. Marine mammal migration has also been noted to occur through the monument. Researchers consider the monument area to be a marine mammal hotspot.