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Blue Whale (Balaenoptera musculus)

Status | Species Description | Habitat | Distribution | Population Trends | Threats | Conservation Efforts | Regulatory Overview | Taxonomy | Key Documents | More Info

Status

ESA Endangered - throughout its range
MMPA Depleted - throughout its range
CITES Appendix I - throughout its range

Species Description

Weight:
up to 330,000 pounds (150,000 kg)
Length:
up to nearly 110 feet (33 m), depending on location (blue whales are largest in the Antarctic)
Appearance:
long body with mottled gray color pattern that appears light blue when seen through the water
Lifespan:
unknown, but sexually mature around 5-15 years
Diet:
primarily krill
Behavior:
births and mating mostly take place in the winter

Blue whales are baleen whales and are found worldwide. Blue whales in the Northern Hemisphere are generally smaller than those in the Southern Hemisphere. In the North Atlantic and North Pacific, they can grow up to about 90 feet (27 m), but, in the Antarctic, they can reach a up to about 110 feet (33 m) and can weigh more than 330,000 pounds (150,000 kg). Like other baleen whales, female blue whales are somewhat larger than males.

Blue whales have 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 (hence, the "blue" whale) when seen through the water.

The primary and preferred diet of blue whales is krill (euphausiids).

In the North Atlantic, blue whales feed on two main euphausiid species (Thysanoessa inermis and Meganyctiphanes norvegica). In addition, T. raschii has 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 pacifica and secondarily on Thysanoessa spinifera.

While other prey species, including fish and copepods, may be part of the blue whale diet, these are not likely to contribute significantly.

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.

Habitat

Blue whales are found worldwide, from sub-polar to sub-tropical latitudes. Poleward movements in spring allow the whales to take advantage of high zooplankton production in summer. Although blue whales are found in coastal waters, they are thought to occur generally more offshore than other whales.

Distribution

Blue whales are found in all oceans and are separated into populations by ocean basin in the North Atlantic, North Pacific, and Southern Hemisphere.

They migrate seasonally between summer and winter, but some evidence suggests that individuals remain in certain areas year-round. Information about distribution and movement varies with location, and migratory routes are not well known. In general, distribution is driven largely by food requirements--they occur in waters where krill is concentrated.

In the North Atlantic Ocean, their range extends from the subtropics to the Greenland Sea. Blue whales are most frequently sighted in the waters off eastern Canada, with the majority of recent records from the Gulf of St. Lawrence, where they are present throughout most of the year. They are most common during the summer and fall feeding seasons and typically leave by early winter. Although they are rare in the shelf waters of the eastern U.S., blue whales are occasionally seen off Cape Cod, MA. It is believed this region may represent the current southern limit of the blue whales' feeding range. In addition, some evidence suggests that blue whales occur infrequently in the Gulf of Mexico and the Caribbean. Blue whales in the North Atlantic probably exist in two distinct populations.

In the North Pacific Ocean, blue whales range from Kamchatka to southern Japan in the west and from the Gulf of Alaska and California south to Costa Rica in the east. They occur primarily south of the Aleutian Islands and the Bering Sea.

Blue whales in the North Pacific probably exist in two sub-populations:

The Eastern stock is believed to spend winters off of Mexico and central America, and feed during summer off the U. S. West Coast and, to a lesser extent, in the Gulf of Alaska and central North Pacific waters.

The Central stock appears to feed in summer in the southwest of Kamchatka, south of the Aleutians, and in the Gulf of Alaska (Stafford, 2003 and Watkins et al., 2000). In winter, they migrate to lower latitudes in the western Pacific and, less frequently, in the central Pacific, including Hawaii (Stafford et al., 2001).

Blue whales accompanied by young calves have been observed often in the Gulf of California from December through March, and, thus, at least some calves may be born in or near the Gulf of California (Sears, 1990); this area is probably an important calving and nursing area for the species.

In the northern Indian Ocean, there is a "resident" population. Blue whale sightings have been reported from the Gulf of Aden, Persian Gulf, Arabian Sea, and across the Bay of Bengal to Burma and the Strait of Malacca. The migratory movements of these whales are unknown.

In the Southern Hemisphere, distributions of two subspecies (B. m. intermedia and B. m. brevicauda) seem to be segregated. B. m. intermedia occurs mainly in relatively high latitudes south of the "Antarctic Convergence" and close to the ice edge. B. m. brevicada is typically distributed north of the Antarctic Convergence.

Population Trends

Blue whales were significantly depleted by commercial whaling activities worldwide.
  Southern Hemisphere North Pacific North Atlantic
Pre-whaling ~175,000 4,900 1,300
Current ~2,000 ~2,500 ~500

Table 1. Global abundance estimates for blue whales by ocean basin (IWC, 2007).

The latest U.S. stock assessments of blue whales include data for various stocks, including areas of the Pacific and Atlantic Oceans.

While there is no current estimate for the number of blue whales in eastern North Atlantic waters, some data have been collected for blue whales in certain areas. In 1997, 32 individuals were photo-identified in Icelandic waters. Additional studies have suggested that the population in Iceland and neighboring waters may be in the high hundreds (Gunnlaugsson and Sigurjónsson, 1990) or even greater than 1,000 (Christensen et al., 1992). Sightings data off the west and southwest coasts of Iceland suggest the population has been increasing at about 5% per year since the late 1960s (Sigurjónsson and Gunnlaugsson, 1990).

Threats

The primary threats currently facing blue whales are:pic

Additional threats that could potentially affect these populations include:

Historically:

Mortality and serious injury caused by ship strikes can be a threat to blue whales. The average number of blue whale mortalities in California attributed to ship strikes averaged 0.2 per year from 1998-2002. In September 2007, three blue whale deaths were confirmed to be caused by ship strikes in the Santa Barbara Channel off Southern California; these deaths were part of a larger Unusual Mortality Event.

In the western North Atlantic, at least 9% of whales in the Gulf of St. Lawrence have injuries or scars attributed to contact with ships (Sears et al., 1990). This area has a relatively high risk of ship strikes, because the St. Lawrence Seaway has heavy ship traffic during the time of year when blue whales are relatively abundant.

Though there is a lack of observed fisheries interactions in recent years, incidental take in fisheries threaten blue whales for two reasons. First, past records of entanglements suggest that interaction with fishing gear may affect blue whales. Second, entanglement rates may be underestimated because blue whales may break through or carry away fishing gear, perhaps suffering unrecorded subsequent mortalities or serious injuries. It is also likely that stranding data underestimate the number of whales killed by fishing gear, because most whales do not drift far enough to strand on beaches or to be detected floating nearshore. Direct observation of mortality is rare, but at least two documented cases of dead blue whales are apparently from the effects of entanglement in fishing gear (one in 1987 off Stellwagen Bank and the other in the 1990s in the Gulf of St. Lawrence).

Anthropogenic noise, habitat degradation, and vessel disturbance are additional concerns. However, there is little evidence available to describe or quantify the impacts of these threats on blue whales. For example, while anthropogenic noise may threaten other cetaceans, little is known about whether, or how, vessel noise affects blue whales.

Habitat degradation (for example, chemical pollution) has occurred in some areas of the North Atlantic (like the St. Lawrence River), but the impacts of this degradation are understudied have not been proven to affect blue whales (O'Shea and Brownell, 1994). Vessel disturbance (like whale-watching boats) may affect blue whales, but there is no direct evidence to demonstrate that persistent close approaches by tour boats has a negative effect on them.

Whaling was a threat to blue whales. From the 1890s-1966, blue whales were hunted in all the world's oceans, and their populations were significantly reduced. At least 9,500 blue whales were taken by commercial whalers throughout the North Pacific from 1910-1965 (Ohsumi and Wada, 1972) and at least 11,000 were taken in the North Atlantic from the 1890s-1960s (Sigurjónsson and Gunnlaugsson, 1990).

In 1966, the IWC banned commercial whaling for blue whales and no whaling (neither aboriginal subsistence nor commercial) occurs now. However, illegal whaling for blue whales has been documented or is likely to have occurred. A small number of illegal kills of blue whales have been documented in the Northern Atlantic off Canada and Spain, and in the eastern North Atlantic. Blue whales were also killed in the Southern Hemisphere by the Soviet Union after 1966 (Zemsky et al., 1995a, 1995b). Some illegal whaling by the USSR also occurred in the North Pacific (Yablokov, 1994), and it is likely that blue whales were among the species taken by these operations, but the extent is not known. Norwegian whaling operations target only minke whales, and the commercial whaling stations in Iceland, Spain, and the Portugese islands of the Azores and Madeira remain officially closed. Therefore, whaling activities, unless they are resumed, are not regarded as a threat to blue whale populations.

Conservation Efforts

Conservation actions for the blue whale are ongoing and include:

In 1998, NMFS published a Blue Whale Recovery Plan [pdf]. The Plan details the comprehensive and long-term conservation efforts for blue whales. In April 2012, we announced that we intend to update the recovery plan for the blue whale and requested comments and information from the public.

Regulatory Overview

The blue whale is listed as endangered throughout its range under the ESA, and, thus, is listed as "depleted" throughout its range under the MMPA. Internationally, blue whales received complete legal protection from commercial whaling in 1966 under the International Convention for the Regulation of Whaling.

Taxonomy

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Balaenopteridae
Genus: Balaenoptera
Species: musculus

Key Documents

(All documents are in PDF format.)
Title Federal Register Date
Notice of Intent To Update a Recovery Plan for the Blue Whale and Prepare a Recovery Plan for the North Pacific Right Whale 77 FR 22760 04/17/2012
Recovery Plan n/a 07/1998
ESA Listing Rule 35 FR 18319 12/02/1970
Stock Assessment Reports n/a various

More Information

References

 

Updated: February 10, 2016