Maximum length of 30 metres.

Blue-grey, mottled in appearance. Skin of some individuals has yellow-brown patches caused by diatoms.

Tail flukes are sometimes raised prior to final dive,

Very broad tail, size can be up to 1/4 of body length. Straight or slightly concave bottom edge with a slight notch in the middle.

Tall, slender and vertical blow, upwards of 9 metres in height.

Very broad, flattened, U-shaped head.

Dorsal fin is variable in shape from triangular to curved toward the back and rounded at the tip.

Dorsal fin 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.

Blue whales feed on zooplankton, most commonly a variety of euphasiid (krill) species, as well as some copepods. 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.

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.

Blue whales can be found in both coastal and pelagic waters, although sightings are rare in B.C.  The rarity of sightings suggests their numbers are currently very low (significantly less than 250 mature individuals).

Blue whales appear to be migratory, spending summer month in higher latitudes and winter in lower latitudes. 

Blue whales can be confused with fin and sei whales: the dorsal fin of a blue whale appears tiny relative to their body size and is set further back than the dorsal fin of a sei or fin whale. Blue whales are often paler than other species with distinctive mottled patterns. Blue whales will sometimes display their tail flukes when diving, a behaviour that is very rarely seen in fin and sei whales.

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.

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). The blue whale is designated as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).