Morphometric analysis of Chilean blue whales and implications for theirtaxonomy
Luis A. Pastene, Jorge Acevedo and Trevor A. Branch
International Whaling Commission
In the Southern Hemisphere, blue whales are currently divided into two subspecies, Antarctic blue whales (Balaenoptera musculus intermedia) and pygmy blue whales (B. m. brevicauda). Pygmy blue whales occur in the western and northern Indian Ocean, southern and southwestern Australia to Indonesia, New Zealand, and the Eastern Tropical Pacific to Chile. Their taxonomic status is in flux, with debate about whether northern Indian Ocean blue whales (pygmy) and Chilean blue whales each should be listed as separate subspecies. Length frequencies of sexually mature female blue whales from several regions of the Southern Hemisphere, call type, and genetics, have been used to propose that Chilean whales are a separate subspecies from pygmy blue whales throughout the Indian Ocean. This interpretation has been accepted by the Society for Marine Mammalogy’s List of Marine Mammal Species and Subspecies. Here, we provide crucial morphometric data to directly address this taxonomic question that were obtained in a biological survey during the 1965/66 Chilean whaling season by a Japanese whaling company. The data for this season consist of sex, total body length, length from tip of snout to center of eye, and length from notch of flukes to anus for 60 blue whales ranging from 21.2 to 24.9 m in total length. The data provide strong evidence that maximum body length, fluke-anus measurement, as well as the ratio of fluke-anus to total body length, are different among Antarctic, pygmy and Chilean blue whales, with the values of the Chilean blue whales being intermediate between pygmy and Antarctic blue whales. These results are similar to those obtained for the distribution of total body length of sexually mature females, and they are also consistent with the available genetic data and differences in song types among regions, and strongly support the suggestion that Chilean blue whales should be considered a separate subspecies.