Size
The blue whale is the largest animal known ever to have existed.[44][45][46] Some studies have estimated that certain shastasaurid ichthyosaurs and the ancient whale Perucetus could have rivalled the blue whale in size, with Perucetus actually being heavier with a mean weight of 180 t (180 long tons; 200 short tons).[3][47] However, these estimates were based on fragmentary remains, and the proposed size for Perucetus was disputed by studies in 2024.[4] Other studies estimate that, on land, large sauropods like Bruhathkayosaurus (mean weight: 110–170 tons) and Maraapunisaurus (mean weight: 80–120 tons) might have rivalled the blue whale, with the former even exceeding the blue whale based on its most liberal estimates (240 tons). However, these estimates were based on even more fragmentary specimens that had disintegrated by the time estimates could be made.[5]
The International Whaling Commission (IWC) whaling database reports 88 individuals longer than 30 meters (98 ft), including one of 33 meters (108 ft).[48] The Discovery Committee reported lengths up to 31 meters (102 ft).[49] The longest scientifically measured individual blue whale was 30 meters (98 ft) from rostrum tip to tail notch.[50] Female blue whales are larger than males.[36][51] Hydrodynamic models suggest a blue whale could not exceed 33 metres (108 ft) because of metabolic and energy constraints.[52]
The average length of sexually mature female blue whales is 22.0 meters (72.1 ft) for Eastern North Pacific blue whales, 24 meters (79 ft) for central and western North Pacific blue whales, 21–24 meters (68–78 ft) for North Atlantic blue whales, 25.4–26.3 meters (83.4–86.3 ft) for Antarctic blue whales, 23.5 meters (77.1 ft) for Chilean blue whales, and 21.3 meters (69.9 ft) for pygmy blue whales.[48][53][54]
In the Northern Hemisphere, males weigh an average 100 metric tons (220,000 lb) and females 112 metric tons (247,000 lb). Eastern North Pacific blue whale males average 88.5 tonnes (195,000 lb) and females 100 tonnes (220,000 lb). Antarctic males average 112 tonnes (247,000 lb) and females 130 tonnes (290,000 lb). Pygmy blue whale males average 83.5 tonnes (184,000 lb) to 99 tonnes (218,000 lb).[55] The weight of the heart of a stranded North Atlantic blue whale was 180 kg (400 lb), the largest known in any animal.[56] The record-holder blue whale was recorded at 173 tonnes (190 short tons),[57] with estimates of up to 199 tonnes (220 short tons).[58]
In 2024, Motani and Pyenson calculated the body mass of blue whales at different lengths, compiling records of their sizes from previous academic literatures and using regression analyses and volumetric analyses. A 25 metres (82 ft) long individual was estimated to weigh approximately 101–119 tonnes (111–131 short tons), while a 30 metres (98 ft) long individual was estimated to weigh approximately 184–205 tonnes (203–226 short tons). Considering that the largest blue whale was indeed 33 metres (108 ft) long, they estimated that a blue whale of such length would have weighed approximately 252–273 tonnes (278–301 short tons).[4]
During the harvest of a female blue whale, Messrs. Irvin and Johnson collected a fetus that is now 70% preserved and used for educational purposes. The fetus was collected in 1922, so some shrinkage may have occurred, making visualization of some features fairly difficult. However, due to this collection researchers now know that the external anatomy of a blue whale fetus is approximately 133 mm. Along with during the developmental phases, the fetus is located where the embryonic and fetal phases converge. This fetus is the youngest gestational age of the specimen recorded.[59]