The humpback whale can grow to around
18m in length and weigh as much as 40,000 kg when fully grown. Females are generally slightly larger than males. Newborn calves are approximately 4.5 m long and weigh
680 kg. The body is stout and massive and the throat and chest are strongly furrowed,
allowing the mouth to expand to take in huge amounts of water during feeding. The body is dark grey or black and the underside
may be white or grey, while the pectoral fins are also often white. The humpback’s
pectoral fins are the longest of all cetaceans, measuring one third of the body length (and so could be up to 6 m long). Both the leading edge of the pectoral fins and the trailing edge of the tail flukes are bluntly serrated in an irregular fashion. Rounded tubercules are present on the upper and lower jaw, and there are between 270 – 400 baleen plates in the mouth that are used for filter feeding. The dorsal fin is located about two-thirds of the way along the back and can be somewhat variable in size and shape, from a vague ridge to notably falcate (upright and curved). The broad tail fluke has a distinct indentation in the centre. Patterns on the underside of the flukes are unique and can be used to identify individuals. When breathing at the surface, the blow is usually low, rounded and bushy in shape. As the whale commences its dive it often arches its back strongly - hence the name ‘humpback’.
Perhaps the most acrobatic of whales; humpbacks may leap almost completely out
of the water, also slapping their tails and pectoral fins on the water surface, possibly as a means of communication. In 2008 a large humpback whale was photographed
breaching clear of the water by a bird watching trip off the Scilly Isles.
© PGH Evans - Sea Watch Foundation
Humpback whales are pelagic when migrating, but otherwise are found over the
continental shelves. They also congregate near seamounts or reefs where upwelling
deep ocean currents bring nutrients to the surface and produce rich feeding areas.
Humpback whales migrate annually between their winter breeding grounds in the
tropics and summer feeding grounds in the polar regions, the longest known migration of any mammal. These round trips can cover more than 16,000 km. Little is
known of their reproductive biology, but the female gives birth to a single calf every
two or three years after a pregnancy of about 12 months. The calf is dependant upon the mother for one, or occasionally two, years. The whales reach sexual maturity at between 4 and 10 years and may live for 50 years or more.
Humpback whales do not appear to form long term, stable social groups and
outside the breeding season they are often solitary. Large competitive groups of males may occur during the breeding season. At other times animals may associate to feed cooperatively. Humpbacks feed on plankton and shoals of small fish, using their baleen plates to filter prey from the seawater in each 60,000 litre mouthful. Groups of humpback whales have been recorded working together to feed on shoals of herring where one animal will create a net of bubbles by exhaling continuously in a circle underneath a shoal of fish, forcing them towards the surface. The other whales then swim upwards through the bubble net together with mouths agape to the surface, enabling them to consume a significant quantity of food in one go. When feeding on less active prey they slowly skim the plankton layer.
Humpbacks produce a range of sounds, apparently for communication. Some sounds may be connected with feeding behaviour, whilst the males produce long, complex ‘songs’, possibly to attract females in the winter breeding season.
Whalers hunted humpbacks extensively during the 20th century for oil, meat and whalebone (baleen) and may have wiped out 90% of this species worldwide. Approximately 200,000 animals were killed in the southern hemisphere between 1904 and 1983. Some hunting is still carried out by isolated aboriginal fishing communities.
Ship strikes are uncommon, but entanglement in fishing gear is probably the biggest current threat to humpbacks. Very young or debilitated humpback whales may be attacked by orcas or large pelagic sharks.
In July 2010 a 7 m long juvenile humpback was seen circling the Stones Reef marker buoy in St Ives Bay, possibly after being separated from its mother. The same animal washed ashore dead near Lelant a few weeks later. A year later another young humpback was reported in St Ives bay, this time entangled in a trawl net. British Divers Marine Life Rescue (BDMLR) attempted to cut the whale free but without success, however apparently the same animal was seen a week later, the net was gone and the animal appeared to be feeding normally.