Blue Whale

B

Vocal Sounds

Blue whales produce loud, low-frequency, moanlike calls that can travel over thousands of kilometers underwater. Most of these sounds are below the range of human hearing but can exceed 180 decibels—the loudest sound made by any animal and louder than the noise of a jet aircraft taking off. Blue whales likely use these calls to communicate, enabling the members of a group to remain in contact across a vast expanse of ocean. Males also produce special calls that may help them find mates.

Like other baleen whales, blue whales are not thought to use high-pitched sounds to echolocate prey the way toothed whales do. However, some scientists think blue whales may navigate using the underwater echoes from their low-pitched calls, which could reveal the shapes of land forms and other features on the seafloor.

V

Diet and Feeding

Blue whales feed by lunging open-mouthed into dense groups of small sea creatures such as krill, zooplankton, or fish. As water and food rush into the whale's mouth, more than 60 throat pleats expand so that the whale’s throat, or gular pouch, forms a huge bag that extends from the front of the whale’s snout to its navel. The whale then partially closes its mouth, leaving a small gap, and forces water past 270 to 390 pairs of wide, black, fringed baleen plates that hang from the roof of the mouth. The plates act as a sieve, catching food inside the fringes. Blue whales often lunge through their prey side by side, apparently using each other to block the escape of their prey.

Blue whales commonly feed in Arctic and Antarctic waters during the summer, when krill is plentiful and found in large swarms. Blue whales may also feed on krill or plankton where there are upwellings of cold currents. The whales can live off stored blubber when they migrate into warmer regions where krill is less available.

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The only natural predators on blue whales are killer whales. Pods of killer whales have been seen attacking blue whales, although how common or how successful such attacks are is not known.

VI

Reproduction

Blue whales generally reach sexual maturity between the ages of eight and ten years. Mating occurs in the summer season, but not much is known about courtship behavior. Male and female blue whale pairs have been seen together for periods of up to three weeks. If a third whale approaches the pair, the whales may engage in vigorous splashing displays.

Mature females may give birth once every two or three years. The gestation period lasts about 11 months. A single young is usually born the following spring; twins are rare. The females migrate to warm regions to give birth. The young nurse for seven or eight months, gaining as much as 90 kg (200 lb) per day.

VII

Conservation Status

Blue whales were not targeted by the whaling industry until the late 1800s after faster steam-powered ships were developed. The peak slaughter of blue whales occurred in the 1930s when explosive harpoons and factory ships that could process enormous whale carcasses became available. Blue whales were heavily hunted for oil, baleen, meat, and other products from the 1930s to the 1960s. The largest numbers of blue whales were taken in the Southern Ocean around Antarctica.

This intensive hunting of blue whales nearly caused the extinction of the species, which may have had a population before whaling of more than 200,000. The International Whaling Commission imposed a ban on killing blue whales in 1966. Blue whales are now protected and may be gradually returning in several areas of their range. Since 1985, blue whales feeding in Monterey Bay, California, have become a familiar sight in late summer. Scientists estimate a global population of blue whales of up to 15,000.

The blue whale is classified as an endangered species. It is protected under the United States Endangered Species Act and the Marine Mammal Protection Act (MMPA). The blue whale is listed as endangered on the World Conservation Union (IUCN) Red List. It is also listed as threatened with extinction on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which prohibits international trade in specimens for commercial purposes.

Reduced populations of krill could affect blue whales as well as other marine animals that depend on the tiny crustaceans as a primary food source. In the Antarctic, krill feed on algae released by melting sea ice in summer. Shrinking sea ice from global warming means less algae as food for krill. By some estimates, krill populations in the Antarctic may have dropped by 80 percent since the 1970s. In addition, the fishing industry has developed new technologies designed for the large-scale harvesting of krill. If humans take significant amounts of krill from the Antarctic and other regions, blue whales may have difficulty finding food.

Other threats to blue whales include collisions with ships and effects of pollutants in the marine food chain, which may interfere with the animals’ reproduction and immune systems.

Scientific classification: The blue whale belongs to the family Balaenopteridae of the suborder Mysticeti, order Cetacea. It is classified as Balaenoptera musculus. The Northern Hemisphere subspecies is classified as Balaenoptera musculus musculus and the large Southern Hemisphere subspecies as Balaenoptera musculus intermedia. The pygmy blue whale is classified as Balaenoptera musculus brevicauda.

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