Blue Whale

Scientific name: Balaenoptera musculus
Mi’kmaq name:

Description

The Blue Whale is the largest animal known to have ever existed on the planet. It is a rorqual whale, a group of whales characterized by pleated grooves in the skin of the neck that allow the throat to expand during the intake of huge amounts of water during feeding. Blue Whales have between 60 and 88 of these throat grooves running from the throat to mid-body. Their tapered, elongated bodies are widest at the level of the eye, with the head accounting for about one-quarter of the total length. The dorsal fin is relatively small, and the pectoral flippers are pointed. Overall, Blue Whales are a mottled blend of dark and light shades of grey. The pattern of the mottling can vary considerably, but it is unique to each individual, and remains stable over time. It can therefore be used to identify individuals and track their movements and behaviour. The biggest Blue Whale ever recorded was 29.5 m long. Females are generally larger than males. Calves measure about 7 m at birth and weigh about 2 tons.

Distribution and Population

Blue Whales are found in all the oceans of the world. Three subspecies are recognized. The Blue Whale that occurs in Canada is commonly known as the Northern Hemisphere subspecies. Two geographically separated populations exist in Canadian waters: one in the North Atlantic and the other in the North Pacific. The Atlantic population of Blue Whales frequents waters off eastern Canada. During spring, summer, and fall, these whales occur along the north shore of the Gulf of St. Lawrence and off eastern Nova Scotia. In summer they also occur off the south coast of the island of Newfoundland and in the Davis Strait, between Baffin Island and Greenland. They usually migrate south for the winter, but in years of light ice cover, some whales may remain in the St. Lawrence for much of the winter. We do not know how many Blue Whales there are in the Atlantic population, but between 20 and 105 Blue Whales are seen annually in the Gulf of St. Lawrence in photo identification studies. A total of 382 individuals have been catalogued in the Gulf since 1979. About 40% of these return regularly, while the remainder appear to be occasional visitors that typically range outside the Gulf of St. Lawrence.

Habitat

Blue Whales range widely, inhabiting both coastal waters and the open ocean. Individuals belonging to the Atlantic population are frequently observed in estuaries and shallow coastal zones where the mixing of waters ensures high productivity of krill (small shrimp-like crustaceans about 2 cm long), the whales’ main food.

Biology

Blue Whales migrate in small herds, spending the summer in food-rich areas close to the edge of the polar ice, and the winter in temperate waters. They feed almost exclusively on krill and one whale may eat as much as 4 tons per day. Blue Whales feed by gulping large quantities of krill, allowing both the water and crustaceans to enter the mouth. The water pressure causes the throat grooves to expand, allowing the whale to hold huge volumes of water in its mouth. The whale then uses its tongue and the muscles at the bottom of the mouth to push the water out through the baleen. Krill and other planktonic organisms become trapped in the fringes of the baleen plates, and the whale then swallows them. After breathing from 6 to 20 times at the water’s surface over a 1- to 5-minute period, Blue Whales generally dive for 5 to 15 minutes. Dives of 20 minutes are not uncommon, and rare dives of up to 36 minutes have been recorded in the St. Lawrence. Male and female Blue Whales reach sexual maturity at between 5 and 15 years of age, females when they measure from 21 to 23 m long and males at a length of 20 to 21 m. Mating and the birth of young take place during the fall and winter in the warmer southern waters. Females give birth, usually to a single calf, every two or three years after a gestation period of 10 to 11 months. It has been estimated that Blue Whales live from 70 to 80 years. They can swim at speeds of up to 36 km/hr, but typically cruise at 2 to 8 km/hr when they are feeding or travelling. In addition to being the largest animals on earth, Blue Whales are also the loudest: at up to 186 decibels their calls are louder than a jet (which reaches only 140 decibels). The calls, which vary among populations, have been described in some detail, but their function remains unclear. Current indications are that only the males make these long, loud calls

Threats

Past commercial whaling of Blue Whales is the main factor responsible for the decline in the animals’ population. At least 11 000 Blue Whales were harvested in the North Atlantic before 1960. Approximately 1500 of these were harvested in eastern Canadian waters from 1898 to 1951. Since the end of commercial whaling, human threats have included collisions with ships, disturbance from increasing whale-watching activity, entanglement in fishing gear, and pollution (especially oil pollution).

Courtesty of Species at Risk Public Registry, Government of Canada
Website:
www.sararegistry.gc.ca