As of 2021, the International Union for Conservation of Nature (IUCN) recognizes 15 mysticete species (while not yet officially recognizing Rice's whale as a species, it still gives it a conservation status as a distinct population segment). Two species—the North Atlantic right whale (with only around 366 individuals left) and Rice's whale (with less than 100 individuals left)—are considered critically endangered. Three more are classified as endangered (the North Pacific right whale, the blue whale, and the sei whale), one as vulnerable (the fin whale), one as near-threatened (Antarctic minke whale), and one as data deficient (Omura's whale). Species that live in polar habitats are vulnerable to the effects of ongoing climate change, particularly declines in sea ice, as well as ocean acidification.