Mammals

The species is usually seen alone or in small groups of two to three individuals, although aggregations of up to 60 may form in areas where food is plentiful. Blue whales are migratory, with most individuals spending the summer feeding in high-latitude regions and returning to warmer waters in the winter for mating and calving. Since the seasons are reversed in the two hemispheres, the northern and southern populations migrate to areas of low latitude at different times of the year and thus remain separate. Some individuals are thought to remain at low latitudes year round in certain parts of the Indian and Pacific Oceans. The species is thought to feed almost exclusively on small, shrimp-like crustaceans (euphausiids), commonly called krill. To feed, the animals take in large amounts of water and krill and then force the water out through their baleen plates, leaving food trapped on the inner fibres of the baleen. Most feeding takes place at depths of less than 100 m, with dives typically lasting between 10 and 20 minutes. In the summer feeding areas the whales may consume as many as 40 million krill each day, a total weight of 3,600 kg. During the rest of the year the whales do not feed, and appear to live off stored fat. Females give birth every 2-3 years during the winter, in the warmer, low latitude waters. A single calf (rarely twins) is usually born after a gestation period of around 10-12 months. Calves are 7 m long at birth, and weigh around 2,000 kg. They grow rapidly, gaining 90 kg per day until they are weaned after 7-8 months, when they are about 15 m long. Sexual maturity is reached at 5-10 years. Blue whales are thought to live around 80-90 years, although some individuals are estimated to have lived for up to 110 years. The species has virtually no natural predators, although calves may be vulnerable to killer whales or large sharks.

Inhabits the open ocean in both cold and temperate waters. Often found along the continental shelf edge and near polar ice.

It is thought that fewer than 5,000 individuals remain.

Pre-whaling numbers have been estimated at 200,000. Some populations in the Northern Hemisphere appear to be increasing.

Classified as Endangered (EN A1abd) on the 2006 IUCN Red List of Threatened Species. The subspecies have been classified as follows: B. m. musculus: (North Atlantic stock) Vulnerable (VU D1). This population is believed to number no more than 1,500 individuals. B. m. musculus: (North Pacific stock) Low Risk/conservation dependent (LR/cd). This population was estimated at about 2,000 in the early 1990s, with evidence suggesting an increase off the coast of California. B. m. intermedia (southern blue whale): Endangered (EN D). There could be as few as 250 individuals surviving. B. m. brevicauda (pygmy blue whale): Listed as Data Deficient (DD) because of uncertainty about its taxonomic status.

Blue whales were not initially targeted by early whalers because of their enormous size and speed, and the fact that they are so difficult to locate. However, technological advances towards the end of the nineteenth century made capture possible. The whaling industry began to focus on blue whales after 1900, and by the 1960s so many had been killed that the species was pushed to the edge of extinction. More than 360,000 blue whales were taken by whaling fleets in the Southern Hemisphere from 1904 to 1967, when they were given legal protection. More than 8,000 pygmy blue whales were killed but not reported at the time by Soviet whaling fleets in the 1960s and 1970s. Although commercial whaling of the species is now banned, the population is now so small that any further mortalities may severely impact on the survival of the species. The species is still subject to a number of threats, including noise and chemical pollution. The blue whale’s almost total dependence on krill means that it could be vulnerable to major changes in ocean productivity caused by factors such as climate change. There is concern over Japan’s continued hunting of whales for “scientific purposes” as blue whale meat sometimes turns up for sale in markets in Japan.

Commercial whaling of the species has been banned since 1966, and all international trade in the species is prohibited as a result of its listing on Appendix I of CITES (the Convention on International Trade in Endangered Species) and Appendix I of the Convention on Migratory Species (CMS or the Bonn Convention). The species occurs in a number of protected areas throughout its range aimed at protecting the whole ecosystem, and there are whale sanctuaries in the Antarctic, Indian and Southern Oceans. Blue whales are covered by a number of international agreements and several countries have implemented research and conservation programmes for the species. These include identifying areas of critical habitat, investigating species abundance and distribution, and mitigating the threats to the species. The IWC is the co-ordinating body for whale research and conservation.

Blue whales require continued protection and close monitoring into the foreseeable future. Knowledge of blue whales is severely limited by their lack of accessibility for research. Further research into the ecology and threats facing this species is required. International cooperation needed to save this species. Areas of critical habitat should be identified and protected, and the immediate threats must be addressed. Recovery strategies should focus on managing human activities (including fisheries, vessel traffic, whale watching, and activities that cause cetacean habitat degradation and loss) to mitigate negative impacts on the species. International co-operation is essential to the successful recovery of the blue whale. Brazil and Argentina have proposed to establish a sanctuary in the South Atlantic, and New Zealand and Australia hope to create a new South Pacific Sanctuary. Both sanctuaries would provide protection for the southern populations of blue whales, along with many other species. In order to be created, these sanctuaries must be voted for by a majority of the member nations of the IWC.

Ocean Alliance - Whale Conservation Institute (WCI)
This institute was established in order to protect whales and their ocean environment through scientific research and education.

Whale and Dolphin Conservation Society (WDCS)
The WDCS is the global voice for the protection of whales, dolphins and their environment.

UK Biodiversity Action Plan: Grouped Plan for Baleen Whales
This UK collaborative effort aims to monitor, assess and develop a strategic plan to ensure the long term survival of the blue whale.

ARKive. (Oct 2006).

Cetacean Specialist Group. 1996. Balaenoptera musculus. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. Downloaded on 25 July 2006.

Clapham, P. J., Young, S. B. and Brownell, R. L. Jr. 1999. Baleen whales: conservation issues and the status of the most endangered populations. Mammal Review 29(1): 35-60.

International Whaling Commission (IWC)

Nowak, R. M. 1999. Walker’s Mammals of the World. Sixth edition. The Johns Hopkins University Press. Baltimore and London.

Reeves, R. R., Smith, B. D., Crespo, E. A. and di Sciara, G. N. (Compilers). 2003. Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World’s Cetaceans. IUCN/SSC Cetacean Specialist Group. IUCN: Gland, Switzerland.

Whale and Dolphin Conservation Society (WDCS)

Distribution map based on data provided by the IUCN Global Mammal Assessment.