BLUE WHALE (Balaenoptera musculus)
- to a maximum length of 30 metres
- blue-grey, mottled in appearance
- skin of some individuals has yellow-brown patches caused by diatoms
- variable in shape from triangular to curved toward the back and rounded at the tip
- looks very small relative to overall body length - 1/3 metre in height, positioned so far back that it is not seen until after the head has submerged and whale is about to dive, long after the blow is seen
- tall, slender and vertical, upwards of 9 metres in height
- sometimes raised prior to final dive, very broad with a straight or slightly concave bottom edge with a slight notch in the middle
- very broad tail, size can be up to 1/4 of body length
Group size / social behaviour
- very broad, flattened, U-shaped head
Can be confused with
- sei and fin whales – especially from a distance due to the extremely tall blows of all of these species. However, the distinctive blue-grey coloration and vast size of blue whales distinguishes them from all other whales.
Blue whales are a cosmopolitan species with a wide-spread distribution in most of the world’s oceans. They can be found in both coastal and pelagic waters. Due to commercial whaling, their global population has been significantly reduced; at present it is unclear how many blue whales remain in the ocean due to their large range and dispersal, as well as low sampling efforts. In Canada, blue whales are present on the Pacific and Atlantic coasts. Through studying distinctive calls it is believe that there are at least two distinct populations within the north Pacific; one occupies the western and central north Pacific, while the other occupies the eastern north Pacific.
Blue whales appear to be migratory, spending summer month in higher latitudes and winter in lower. Some tropical areas, however, have shown certain whales present year round, indicating possible non-migratory blue whales. The whales that frequent the waters off British Columbia are most likely the same whales that feed off California in the summer/fall and spend the winter months in Mexico and Central America. They are capable of covering long distances in short periods of time; one animal was documented travelling from the Queen Charlotte Islands to the Santa Barbara Channel, a distance of 2500km in 28 days or less. Researchers are able to identify individual blue whales by the pigmentation and mottling patterns on their flanks. Much of this photo-identification has taken place in California, a hotspot for blue whale sightings. In 2007, researchers from Fisheries and Oceans Canada spotted 5 different blue whales off of Haida Gwaii in British Columbia.
Blue whales feed on zooplankton, most commonly a variety of euphasiid (krill) species, as well as some copepods. Blue whales are a ‘rorqual’- meaning they have pleats along their throat. This allows them to expand their throat while feeding, and then expel salt water through their baleen, which acts as a food sieve. To feed, blue whales lunge through swarms of krill, sometimes on their side or back. This may be observed above water, but most surface-feeding probably happens at night, when krill concentrations rise in the water column. Due to their enormous size blue whales must eat several tons of zooplankton a day. This large energetic demand may mean their range and recovery is constrained by food availability. Climate change and other oceanographic shifts may greatly affect zooplankton and, therefore, the blue whale. The majority of feeding happens in high latitude water, usually in productive upwellings along the continental shelf break.
No breeding grounds for the blue whale are known in the world, but it is believed that reproduction happens in the winter in tropical/sub-tropical waters. For example, females and calves are often spotted in the Gulf of California, Mexico. Females have a gestation of 10-12 months and will nurse for 6-7 months. Most likely, the calves are weaned in the summer on the feeding grounds. Females and males reach sexual maturity between 5 and 15 years of age, and a female has a birthing interval of 2-3 years.
The vocalization of a blue whale may be the loudest sound made by an animal. Most of their calls are low frequency and infrasonic; the human ear does not hear them. These types of calls can travel huge distances (100s-1000s of kilometers) and are well-suited for an animal that has such a large dispersal, enabling communication between animals very far apart. Acoustics are increasingly being used to understand the range of the blue whale and to some degree, their abundance. Off British Columbia, blue whale calls are most consistently heard between October and February.
It is unclear exactly how many blue whales would have been present in the north Pacific prior to whaling. However, it is estimated that 9500 blue whales were taken from north Pacific by commercial whalers. In BC, at least 650 blue whales were killed between 1900 and 1967. Blue whales may be preyed upon by killer whales, though this is thought to be an unusual occurrence in most of their range.
STATUS IN CANADA
The blue whale is designated as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).
COSEWIC’s assessment of the Pacific population of the blue whale is as follows:
Blue Whales off the coast of British Columbia are likely part of a population based in the northeastern Pacific. The population was reduced by whaling. The rarity of sightings (visual and acoustic) suggests their numbers are currently very low (significantly less than 250 mature individuals). Threats for blue whales along the coast of British Columbia are unknown, but may include ship strikes, pollution, entanglement in fishing gear, and long-term changes in climate (which could affect the abundance of their zooplankton prey).