Blue whale
Channel: công phạm thành
Date: 09/07/2017

The blue whale has a long tapering body that appears stretched in comparison with the stockier build of other whales.[24] The head is flat, U-shaped and has a prominent ridge running from the blowhole to the top of the upper lip.[24] The front part of the mouth is thick with baleen plates; around 300 plates, each around one metre (3 ft) long,[24] hang from the upper jaw, running 0.5 m (20 in) back into the mouth. Between 70 and 118 grooves (called ventral pleats) run along the throat parallel to the body length. These pleats assist with evacuating water from the mouth after lunge feeding (see feeding below).

The dorsal fin is small;[24] its height averages about 28 centimetres (11 in), and usually ranges between 20 cm (8 in) and 40 cm (16 in), though it can be as small as 8 cm (3.1 in) or as large as 70 cm (28 in).[25] It is visible only briefly during the dive sequence. Located around three-quarters of the way along the length of the body, it varies in shape from one individual to another; some only have a barely perceptible lump, but others may have prominent and falcate (sickle-shaped) dorsals. When surfacing to breathe, the blue whale raises its shoulder and blowhole out of the water to a greater extent than other large whales, such as the fin or sei whales. Observers can use this trait to differentiate between species at sea. Some blue whales in the North Atlantic and North Pacific raise their tail fluke when diving. When breathing, the whale emits a vertical single-column spout, typically 9 metres (30 ft) high, but reaching up to 12 metres (39 ft). Its lung capacity is 5,000 litres (1,300 US gal). Blue whales have twin blowholes shielded by a large splashguard.[24]

The flippers are 3–4 metres (10–13 ft) long. The upper sides are grey with a thin white border; the lower sides are white. The head and tail fluke are generally uniformly grey. The whale's upper parts, and sometimes the flippers, are usually mottled. The degree of mottling varies substantially from individual to individual. Some may have a uniform slate-grey color, but others demonstrate a considerable variation of dark blues, greys and blacks, all tightly mottled.[3]

Blue whales can reach speeds of 50 kilometres per hour (31 mph) over short bursts, usually when interacting with other whales, but 20 kilometres per hour (12 mph) is a more typical traveling speed.[3] Satellite telemetry of Australian pygmy blue whales migrating to Indonesia has shown that they cover between 0.09 and 455.8 kilometers (0.056 and 283.2 miles) per day.[26] When feeding, they slow down to 5 kilometres per hour (3.1 mph).

Blue whales typically swim at a depth of about 13 meters (42.5 feet) when migrating in order to eliminate drag from surface waves. The deepest confirmed dive is 506 meters (1,660 feet).[27]

Blue whales most commonly live alone or with one other individual. It is not known how long traveling pairs stay together. In locations where there is a high concentration of food, as many as 50 blue whales have been seen scattered over a small area. They do not form the large, close-knit groups seen in other baleen species.