Blue whale

Habitat: Generally deep waters (100 - 1000 m); some regions regularly closer to land at depths of 200 m or less.

Description: Largest and heaviest known mammal. Body is robust, head is large (up to 25% of total length) with broad snout. Colouration generally blueish grey, occurs in two main varieties; dark blueish grey, mottled with sparse paler patches, or paler with dark mottled patches. Sometimes mustard yellow on belly (from algae). Young animals usually paler. Baleen plates are black, fringed, relatively short (90 cm long, 50 cm wide), with 260 - 400 on each side of upper jaw. Flippers are long (up to 15% of total body length), slim, underside and tips white or pale grey-blue. 55-88 grooves in throat extend more than 1/2 down the body.

Size: Adult length between 24 - 26 m, females are larger. Southern hemisphere individuals may reach 33.6 m.

Weight: 80,000 to 150,000 kg.

Lifespan: Estimated at 30 years but may be as much as 80 - 90 years.

Distribution: Worldwide, mainly in warm temperate - subtropical waters during winter and cold temperate and polar seas in the winter. Small numbers occur in deep waters of Faroe - Shetland Channel and Rockall Trough, south to Bay of Biscay.  Probably winter and breed in tropical and subtropical seas, although some remain in high latitudes during winter. Early 20th century whaling records indicate presence around British Isles; small numbers regularly passed west of Great Britain and Ireland in deep waters off edge of continental shelf.

Diet and feeding: Feeds mainly in deep waters at 100 - 200 m but may also be seen feeding at surface, where it may lunge vigorously on sides or vertically. Feeds almost exclusively on planktonic crustaceans, mostly euphausiids (krill), although also takes copepods and, less frequently, amphipods, cephalopods, and (perhaps accidentally) small fish.

Breeding: Gestation 10 - 11 months. Lactation 6 - 8 months (weaning occurs when young reaches length of around 16 m). Calving interval 2 - 3 years. Sexual maturity reached at 5 - 15 years, but usually 8 - 10 years for both sexes.

Conservation status and population: Listed by IUCN as endangered. North Atlantic population probably numbers no more than 1,500 animals, mostly in the west.

Historically, populations worldwide have been severely depleted by whaling; during the peak of exploitation in the 1930 - 1931 season, 11,000 individuals were taken in the North Atlantic. Stocks slightly recovering in eastern North Pacific, and possibly in the North Atlantic. Contaminants such as PCBs may have impact on reproduction. Little information on accidental capture in fishing gear, but thought to be relatively unimportant. Collisions with ships occur. Sound disturbance from shipping and whale watching boats may have negative effect. Likely vulnerable to climate change due to dietary reliance on euphausiids.

Identification

Largest whale. Dorsal fin is very small and more than 2/3 along the back, only visible just prior to diving. Blow is dense, broad, up to 12 m. Flukes lifted only slightly before diving; they are predominantly grey, broad and triangular with slight median notch; some individuals have white patches on ventral side of tail. Relatively non-social; usually seen singly or in pairs, but large gatherings of >50 individuals may be seen around concentrations of food.

Vocalisations: Vocal throughout year, peaks midsummer into winter. Moans at 17 - 30 Hz last 15 - 38 s, sometimes with higher-pitched pulses. Clicks at 6 - 8 or 21 - 31 kHz. Low frequencies are very loud and are thought to allow communication over great distance, possibly even across ocean basins.