Blue whales have a long, bluish gray, tapered body; a flat U-shaped head; and a very small dorsal fin positioned far back on the body. The whales produce underwater sounds that can occur as singular calls or as phrases combined to form songs. Image credit: NOAA Fisheries.
Blue whales are the largest living mammal species. Their long, slender bodies can reach lengths of 30.5 m (100 ft) and weigh up to 160 tons. Feeding mostly on krill with the use of long baleen plates, these animals can consume as much as six tons of krill per day. Blue whales have been found in all ocean basins except the Arctic. Currently, there are four recognized subspecies of blue whales: B. musculus intermedia (Antarctic or Southern blue whale, Southern Ocean), B. musculus musculus (Northern blue whale, N. Atlantic, N. Pacific); B. musculus indica (Indian Ocean blue whale, Indian Ocean); and B. musculus brevicauda (“pygmy blue whale”, sub-Antarctic waters of the Indo-Pacific Ocean and SE Atlantic).
Blue whales produce stereotyped calls throughout the year. These calls have been described as pulses, grunts, groans, and moans, and are typically in the 15-40 Hz range, often below the threshold of human hearing. In addition to being some of the lowest frequency animal sounds produced, blue whale vocalizations are also recognized among the most intense. The source level of a vocalizing Antarctic blue whale has been estimated to be 189 underwater dB.
Side view of a blue whale, showing the mottled coloration pattern on its body and its small dorsal fin. Photo courtesy of Thomas Jefferson
Scientists use passive acoustic monitoring (PAM) to clarify distribution patterns and enhance conservation and management measures for these endangered whales. The blue whale acoustic repertoire has two main sound types: songs which consist of a variety of regularly repeated, relatively long units; and short, down-swept D calls that are produced irregularly. Song units, each lasting about 15-20 s, can be produced as singular calls or combined into phrases that, when repeated, form bouts of song. D calls are produced by both sexes and are thought to be used as “contact calls” between groups of two or more whales. There are distinct geographic variations in song types that help scientists distinguish separate populations. D calls, however, do not have obvious geographic variation.