Humpback whale (Megaptera novaeangliae)

Humpback whales, or just ”humpbacks”, are a highly migratory species that is found in all the world’s oceans, and are one of the most easily recognized and best known of the large whales. They are stout for their length compared to other members of the family Balenopteridae (the rorquals) and they have a rounder head that is covered in large bumps.

Humpback whale

Humpback whale. Photo: tromsofoto.net

Humpbacks are one of the most easily recognized and best known of the large whales. They are stout for their length compared to other members of the family Balenopteridae (the rorquals) and they have a rounder head that is covered in dermal tubercles (large nodules/bumps). They have remarkably long flippers that are scalloped on their anterior side and are almost always white on the ventral surfaces. The dorsal fin of humpbacks is low and highly variable in shape. Their overall colouration is black, but many individuals have white markings on the throat and abdomen that can extend onto the head and even down the sides on some animals. Average length is around 14 m and females are somewhat bigger than males. Humpbacks flukes are large and deeply notched in the centre and they almost always show their flukes when leaving the surface. The ventral colouration of the flukes is distinctive and the pattern of white markings is specific to an individual. Calves are born weighing about two tonnes and are four to five metres long. They often exhibit exuberant surface behaviour (breaching, lobtailing, flipper-slapping, lunging, fluking and spy-hopping/bringing their eyes out of the water). The blow is distinctive because it is almost as wide as it is high (up to three metres).

Distribution

Humpbacks are a highly migratory species that is found in all the world’s oceans. They spend the winter months in tropical calving grounds, and the spring, summer and autumn at mid or high latitudes. Northern Hemisphere populations move north in summer and south for the winter. Although whales from a broad area congregate on a single wintering ground in the West Indies, each seems to be very faithful to its distinct summer location somewhere between the Gulf of Maine and the high arctic regions in Norway, as far north as Svalbard.

Ecology

There are estimated to be 18-20,000 humpback whales in the North Pacific and approximately 12,000 in the North Atlantic and approximately 50,000 in the Southern Ocean. Global estimates are not available. Humpback whales are loosely social and are often found in small, unstable groups. They are highly migratory, moving between warm water breeding areas and highly productive, cold-water foraging grounds on a seasonal schedule. They are typically found in coastal or shelf waters. During the winter months male humpbacks sing to attract females and all members of a population have common elements in their songs that shift simultaneously through time. The humpback whale’s song is probably its best-known character. This species is very vocal, making a wide variety of sounds including moans, groans, cries, squeals, chirps and clicks in addition to the elaborate mating songs which incorporate a variety of types of sounds. Humpback whales are known for their spectacular aerial behaviours. They also perform several unusual modes of feeding including a form of cooperative feeding using bubble-nets. Humpback whales are not particularly deep divers; they dive for an average of seven minutes, but dives up to 30 minutes have been documented. Humpback whales have a broad diet, feeding on krill and other schooling invertebrates as well as a wide variety of small schooling fishes including herring, capelin, sand lance, and mackerel.

Killer whales commonly attack humpbacks, although fatal attacks seem to be primarily confined to young animals.

Life history and reproduction

Female humpbacks come into breeding condition in the winter and mate on the wintering grounds. The gestation period is about 11 months, which means that most calves are born in midwinter the following year. Calves remain with their mothers for about a year, so accompany her on the first summer migration following their births. Mating is very competitive among males and a lot of aggressive behaviour takes place in the defence of access to females. Sexual maturity is reached at about five years of age and females usually give birth every second year thereafter. Humpback whales are thought to live approximately 50 years. 

Management status and monitoring

Humpback whales were very heavily exploited during centuries of commercial whaling. It is thought that most populations were reduced by about 90%. Despite the extreme reductions in numbers, humpbacks seem to be making a strong recovery following protection. Aboriginal people hunt humpback whales in small numbers, but greater mortality levels occur due to entanglement with fishing gear and collisions with ships. This species is protected in Svalbard. Humpbacks have shown a strong recovery following the cessation of commercial whaling and they are sightings in Svalbard are increasing, particularly on the west coast of Spitsbergen and in the Hinlopen and Olga Straits. In 2012 a white humpback was observed; this was the first official registration of a leukistic individual in the northern hemisphere (and in the Atlantic Ocean).

MOSJ indicators (Environmental Monitoring of Svalbard and Jan Mayen):

Awaiting results from MOSJ…