M A R I N E M A M M A L S O F T H E W O R L D50

Blue Whale

adult Pygmy blue Whale, 22 m

adult nominate race, 27 m

adult Pygmy blue Whale, dorsal view, 22 m

adult nominate race, dorsal view, 27 m

smaller and proportionately more compact than true blue whales

mottling ends, making head appear dark (all blue whales)

U-shaped, elongated and rather broad rostrum

proportionately large flippers with distinct kink to leading edge (all blue whales)

proportionately elongated with slender rear body

deep tailstock

Tall, columnar blow; massive shoulder/splashguard emerge; in prepararing for deep dive, body rolls, tiny dorsal fin briefly emerges, and tailstock is strongly arached; flukes occasionally lifted.

built, with narrower heads and more prominent, less set-back dorsal fins, stronger dorsal/ventral contrast, and very different dive sequences/behaviour.

Pygmy Blue Whale (brevicauda) breaks the surface with the rostrum/splashguard and shoulders; blow dis-persed by wind.

tiny nub-like (variable) dorsal fin (all blue whales)

greyish/mottled body: can appear pale grey, purple-grey or blue-grey (all blue whales)

darker underbody (all blue whales) the largest whale with

massive elongated rear bodyshorter and more rounded rostrum relatively short and

slender tailstock

massive shoulder and splashguard (all blue whales)

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VariaTionAge/sex Perhaps estimable by size. Physical notes 20–33.6 m and 80–150 (exceptionally 190) tons (the largest whale); ™ slightly larger than ¢. Newborn 6–7 m and 2.5–4 tons. Taxonomy Varies in size and coloration, both individually and geographically. Status of the various forms highly controversial and information to permit at-sea identification lacking. However, at least Pygmy Blue Whale B. m. brevicauda, of S Hemisphere, may merit specific recognition. Other forms include B. m. intermedia (Southern Blue Whale) in S Hemisphere (north to 22ºS off S America and

R O R Q U A L S W I T H S T R E A M L I N E D B O D I E S

Pygmy Blue Whale (brevicauda) is relatively compact in structure and length.

6ºS off W Africa, though winter/breeding range almost unknown), B. m. indica (Indian Ocean Blue Whale) in N Indian Ocean, and nominate B. m. musculus (Northern Blue Whale) in N Hemisphere. B. m. indica seems morphologically and genetically close to, or even the same as, brevicauda (the name indica has priority). The N Indian Ocean whales, however, have a limited range and seem to undertake a rather unique migration. Hybrids: Blue × Fin recorded in N Atlantic (with fertile offspring), and possibly Blue × Humpback in S Pacific.

DiSTribuTion & PoPulaTionSeparate populations in N Pacific, N Atlantic, Indian and Southern Oceans; mainly in cold waters (sometimes near polar ice) and open ocean, but also inshore, at edge of continental shelf, where feeds and possibly breeds. Migrates between summer feeding areas and warmer

seas where winters and breeds. Population Perhaps fewer than 10,000, of which c.5,000 in S Indian Ocean and 710–1,255 in Antarctic waters, whilst in N Hemisphere largest numbers in NE Pacific, where c.3,000 (of which c.2,000 summer off California); c.400 in NE Atlantic, off Iceland and in adjacent waters, and 350+ in NW Atlantic.

ecologyUsually encountered alone or in twos. Migrates in groups of 2–3, rarely more; loose aggregations of up to 50 on feeding grounds,

Blue Whale (nominate) in smooth mid-body roll. Pale/greyish-mottled coloration and diagnostic miniature dorsal fin set well back.

Below: Fluking Blue Whale. Note underside pattern (cf. Fin Whale).

Pygmy Blue Whale (brevicauda) has a pale-mottled body and tiny dorsal fin set well back.