There are 10 cetacean species found in the Southern Ocean; six baleen whales, and four toothed whales. The largest of these, the blue whale (Balaenoptera musculus), grows to 24 metres (79 ft) long weighing 84 tonnes. Many of these species are migratory, and travel to tropical waters during the Antarctic winter.[18] Killer Whales, which do not migrate, nonetheless regularly travel to warmer waters, possibly to relieve the stress the temperature has on their skin.[19]