The blue whale is the largest of all the whales; indeed it is the largest extent animal on the planet. The body of the blue whale is long and slender, and is mottled a bluish-gray. When viewed through the water surface they may appear dappled or uniformly light blue. There is light to extensive mottling on the sides, back, and belly, generally in the form of dark spots on a lighter surface, but sometimes the reverse. A prominent chevron, with the vertex behind the blowholes, marks the transition of coloration between the head and the body. Diatom films on the skin may be seen as an orangish-brown or yellow tinge, a characteristic that gave rise to the alternative name "sulphur-bottom" whale.
The rostrum is broad, flat, and “U” shaped, with a ridge running from the impressive “splashguard” around the blowhole to the tip of the snout. Blue whales have long, slim flippers and a triangular or sickle shaped dorsal fin that is small (less than 33 cm) proportional to the rest of the body. The dorsal fin, located far back on the animal, is often not visible until the animal begins a dive. The broad flukes have a relatively straight trailing edge and a prominent notch. Blue whales have 60 to 68 ventral grooves that extend at least to the naval, and possess 270 to 395 baleen plates per row.
Three subspecies are recognized. In the Southern Hemisphere and northern Indian Ocean, a subspecies called the pygmy blue whale (B. m. brevicauda), which is shorter and has a relatively larger head, has been described. If a good view is obtained, it is possible to distinguish pygmy blue whales from other blue whales at sea. The shape of the body has been described as ‘tadpole-shaped’ (showing a relatively wider head) for the pygmy subspecies, and ‘torpedo-shaped’ (a relatively narrower head) for the standard subspecies. These differences are subtle and require a great deal of experience to reliably distinguish. Some researchers believe that pygmy blue whales also have a tendency to surface without showing the dorsal fin or keel (unlike the standard blue whale, which usually does). However, this is probably not very reliable.
Most adults of the Northern Hemisphere subspecies (B. m. musculus) are 23-27 m long, with females growing larger than males. The Antarctic blue whale (B. m. intermedia) is larger, and generally measures up to 29 m, although a specimen over 33 m was once taken by whalers. The pygmy subspecies (B. m. brevicauda) is the smallest, with a maximum length of only about 24 m. Newborns are about 7 m long. Adults can weigh up to 190 tons, but most adults are 80-150 tons.
Can be Confused With
Blue whales might be confused with fin (B. physalus) or sei whales (B. borealis), but they are much larger than these cogeners. The blue whale can be distinguished from the fin whale because the fin whale’s mouth is asymmetrically colored (the right side is white; the left, gray). Blue whales can be distinguished from sei whales by a shorter dorsal fin, placed further back on the body.
Blue whales are cosmopolitan in range. Populations migrate seasonally, moving poleward in spring to exploit the high productivity of the cold waters and traveling into the subtropics in fall to reduce energy expenditures, avoid ice entrapment, and reproduce in warmer waters. When feeding in cold waters, blue whale distribution is largely determined by food availability. Individuals do not stay in one area for very long, traveling solitarily or in pairs, and are found in both coastal and pelagic environments.
B. m. brevicauda — Antarctica/Southern Ocean, eastern Atlantic Ocean, Indo-West Pacific, sub-Antarctic Southern Indian Ocean and southwest Pacific Ocean
B. m. indica — Indo-West Pacific, Gulf of Aden east to the Bay of Bengal
B. m. intermedia — Antarctica/Southern Ocean, eastern Pacific, eastern Atlantic Ocean, Indo-Pacific Ocean, western Atlantic Ocean
B. m. musculus &mdash eastern Atlantic Ocean, western Atlantic Ocean
Ecology and Behavior
Blue whales are generalists in terms of habitat
Blue whales are long lived, with a lifespan estimated at 30 to 90 years. The age of sexual maturity is uncertain, but estimated to be five to fifteen years for both sexes. Reproductive activity takes place during winter, in the warmer waters of their range, and females breed every two to three years. The specific breeding grounds are not known with any accuracy. Gestation lasts ten to twelve months. Newborns measure seven meters and are nursed six to seven months.
Blue whales are usually seen alone or in pairs. However, scattered aggregations of a dozen or more may develop on prime feeding grounds. Although shorter dives are most common, dives of up to 30 min, generally interspersed with long series of shorter surfacings (at 15-20 sec intervals), have been recorded. Fluking-up is not uncommon, although not all blue whales are "flukers." Remarkably, some blue whales have been observed breaching.
Feeding and Prey
Blue whales feed almost exclusively on crustaceans, particularly euphausiids (krill). Blue whales may ingest two to four tons of food per day. Blue whales are known to feed on the surface and at depth, and in some places have been recorded exploiting deep scattering layers in which plankton are concentrated. They feed by lunging at prey.
Prey species include:
Southern Ocean population: Euphausia superba
North Pacific population: Thysanoessa inermis, T. longipes, T. spinifera, Nematoscelis megalops, Euphausia pacifica, Thysonoessa raschii, Pleuroncodes planipes, Nyctiphanes simplex
The global population of blue whales prior to whaling may have been as high as 300,000. It was not until powerful boats and deck-mounted harpoon cannons were developed that blue whales could be hunted by whalers. From the turn of the twentieth century until the mid-1960’s blue whales were intensively hunted throughout the world’s oceans. During the 1930-1931 hunting season, over 30,000 blue whales were killed worldwide, the highest annual hunt on record.
By 1966, blue whales were protected in all waters by the International Convention for the Regulation of Whaling. Despite protection, the population remains substantially below pre-whaling levels. The IUCN lists three geographically distinct populations: Southern Ocean (endangered, population estimated at 400-1400), North Atlantic (vulnerable, population estimated at up to 4000), and North Pacific (lower risk, population estimated at up to 4000) but considers the pygmy blue whale as “Data Deficient”, in that too little is known about the population to judge its conservation status. In the United States, blue whales are listed as an endangered species and are also protected by the Marine Mammal Protection Act. Some illegal hunting has been documented since 1966, but presently this is not a major threat. Other conservation concerns include entanglement in fishing gear, collisions with ships, and possible threats from low-frequency acoustic research currently underway.
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