Blue Whale

Blue Whale - Description

The blue whale, Balaenoptera Musculus, is a cosmopolitan species of baleen whale. Blue whales in the Northern Hemisphere are generally smaller than those in the Southern Ocean. Maximum body length in the North Atlantic was about 88.5 feet (27 m) and the largest blue whale reported from the North Pacific was about 88 feet (26.8 m). Adults in the Antarctic can reach a maximum body length of about 108 feet (33 m) and can weigh more than 330,000 pounds (150,000 kg).

As is true of other baleen whale species, female blue whales are somewhat larger than males. Blue whales are identified by the following characteristics: a long-body and comparatively slender shape; a broad, flat "rostrum" when viewed from above; a proportionately smaller dorsal fin than other baleen whales; and a mottled gray color pattern that appears light blue when seen through the water.

Blue Whale - Diet

The primary and preferred diet of blue whales is krill (euphausiids). In the North Atlantic, blue whales feed on two main euphausiid species: Thysanoëssa inermisand Meganyctiphanes norvegica. In addition, T. raschiiand M. norvegicahave been recorded as important food sources of blue whales in the Gulf of St. Lawrence. In the North Pacific, blue whales prey mainly on Euphausia pacificaand secondarily on T. spinifera. While other prey species, including fish and copepods, have been mentioned in the scientific literature, these are not likely to contribute significantly to the diet of blue whales.

Blue Whale - Behaviour

Blue whales do not have teeth. Hanging down from the upper jaw are Baleen plates which look like the frayed bristles of a giant hairbrush and are used to sieve food from seawater.

When a blue whale eats, the pleats or grooves on its throat and belly expand to allow it to gulp huge watery mouthfuls of tiny, shrimplike crustaceans called Krill. Water is then forced out between the baleen plates and the food caught on the hairy fringes is then swallowed.

Blue Whale - Habitat

Blue whales inhabit sub-polar to sub-tropical latitudes. Poleward movements in spring allow the whales to take advantage of high zooplankton production in summer. Movement towards the subtropics in the fall allows blue whales to reduce their energy expenditure while fasting, avoid ice entrapment in some areas, and engage in reproductive activities in warmer waters of lower latitudes. Although the species is often found in coastal waters, blue whales are thought to occur generally more offshore than northern right whales and humpback whales.

Blue Whale - Life History

Scientists have yet to discern many details regarding the life history of the blue whale. The best available science suggests the gestation period is approximately 10-12 months and that blue whale calves are nursed for about 6-7 months. Most reproductive activity, including births and mating, takes place during the winter. Weaning probably occurs on, or en route to, summer feeding areas. The average calving interval is probably two to three years. The age of sexual maturity is thought to be 5-15 years. There are no known differences in the reproductive biology of blue whales in the North Pacific and North Atlantic oceans.

Most of the larger whales have a very low reproductive rate: females only have a single calf every 2-4 years. With very small populations this low rate of reproduction means that it may take decades for some species to recover to their former population levels. Even under the best conditions, it will take over a hundred years for the right whale to recover. For some species of whales, the calves are born during the part of the animal cycle when the animals are in warmer waters, and the adults are not feeding.

Blue Whale - Special Features or Habits

Blue whales produce patterned sequences of powerful, low frequency calls, some of them as low as 9 Hz (Mellinger & Clark 2003), making them particularly suited to long-range underwater communication (Tyack & Clark 2000). Blue whales off Western Australia had most energy in the range 10-30Hz (McCauley et al. 2001), while sound source levels may reach up to 188 dB re 1?Pa at 1metre (Richardson et al. 1995). Higher frequency (up to 524Hz) blue whale sounds, thought to be those of pygmy blue whales, have been recorded off Western Australia (Ljungblad et al. 1997, McCauley et al. 2001). Blue whale calls have been recorded during the austral winter in the tropical Pacific and Indian Oceans (Stafford et al. 2004), but have also been recorded off the Antarctic Peninsula during winter (D.Thiele, pers. comm.), confirming variability of migration patterns in this species.

Blue Whale - Location or Region Found

Blue whales are found in oceans worldwide and are separated into populations by ocean basin in the North Atlantic, North Pacific, and Southern Hemisphere. They follow a seasonal migration pattern between summering and wintering areas, but some evidence suggests that individuals remain in certain areas year-round. The extent of knowledge concerning distribution and movement varies with area and migratory routes are not well known but, in general, distribution is driven largely by food requirements. For example, in the Gulf of St. Lawrence blue whales prefer deep waters where krill is concentrated.

Being an open ocean species they are not seen near the coast but mainly in the deeper waters off the continental shelves and ice edges.