Humpback Whales

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Family: Balaenoteridae
Species: Megaptera novaeangliae
Common Name: Humpback Whale

The scientific name is derived from both Latin and Greek. Greek “magas” foro large, “pteron” for wing or fin and, at up to 16ft (5m) in length the pectoral flippers of the Humpback whale are the longest appendages of any animal. The rest of the name derives from Latin “novus” for new and Middle English “angaliae” for England.

The common name derives from distinctive feature of the dorsal fin, which is reduced to a fleshy hump, or hook, that sits on a sort of platform on the back. The dorsal fin frequently has a step or hump which is accentuated when the whale arches its back to begin a dive.

Humpbacks belong to the large group of marine mammals called Cetaceans (see the science page on Melon Headed Whales for more information on this). This group is basically dived into two - those with teeth - Odontocetes, and those without teeth - Mysticetes or baleen whales, there is also an extinct group the Archaeoceti (known only from fossils). The Humpback Whale is a baleen whale; that is a filter feeder, straining plankton or tiny fish through baleen plates.

Appearance 

The Humpback is one of the most energetic and well known of the large whales. It is popular with whale watchers everywhere for its spectacular surface displays - breaching, lobtailing and flipper slapping. It is also one of the easiest whales to identify; from a distance by it’s long pectoral flippers, and close up by its knobby head and low stubby dorsal fin.

Humpbacks can attain a size of 16m or 52ft (females are usually larger than males) and can weigh up to 30 tons. They are black, blue-black or dark grey and usually have a partially white underside. The broad tail flukes have a ragged trailing edge and, like the pectoral fins, have black and white pigmentation. This pattern of pigmentation is as individual to each humpback whale as are our own fingerprints - no two are ever alike, and so it is a useful tool for distinguishing individuals.

Humpback whales have a broad, flat head, which is rounded at the front and constitutes about 1 third of the total body length. The most distinctive feature on the head is a series of knobs or protrubences, each about as big as a ping-pong ball, which cover the flat rostrum (the part of the head in front of the blowholes) and the lower jaw. These knobs are actually hair follicles and each one has a single, coarse hair up to 11/4 inches or 3cm long growing out of it. The presence of the hairs suggests that knobs have some kind of sensory function.

Humpback whales can also be identified by their ‘blow’, which is very distinctive - two columns of vapour emitted from the blow holes on the top of the head. The blow is typically about 2.5-3m tall, and forms a bushy plume that is usually wide in relation to its height

Humpbacks are seen singly, in pairs or in groups of up to 15 animals. Mothers and calves generally stay close during the first year, but during the mating season they may be joined by male escorts.

Distribution 

Humpback whales are widely distributed over all the oceans from the poles to the topics, but there are distinct seasonal changes in their distribution. As with birds, the change in season induces Baleen whales to migrate. Humpbacks spend the winter in high-latitude, cold-water feeding grounds and summer in low-latitude, warm-water breeding grounds. Of course whether they undertake a north-south or south-north migration depends on which hemisphere they are in.

In the southern hemisphere - which is where we have seen Humpback whales, they basically make a south-north migration between the cold-water feeding grounds of the summer (November to May) to the tropical breeding areas of winter (June to October). The humpbacks spend the summer in the krill-rich Southern Ocean surrounding Antarctica and then they migrate to the breeding areas in New Caledonia, Tonga and Polynesia (Dr Michael Poole pers.com.) for the winter. In fact, the greatest confirmed migration of any individual mammal is by a humpback whale -a record previously though to be held by the grey whale; one humpback was identified at feeding grounds near the Artic Peninsula and was seen again at it’s breeding grounds off the coast of Columbia five months later. The shortest swimming distance between these two locations is 5,176 miles (8,334km). Like other Baleen whales, Humpbacks fast throughout much of their migration, living on their blubber and fat for up to eight months of the year. In the case of a female making a migration the total weight loss may be as much as 50%.

Whales are thought to migrate because birth and early development in warm water is important for the calves, but also because the spread of ice across the Antarctic ocean leads to a paucity of food during the winter. Another idea is that baleen whales may breed away from Antarctic waters to avoid predation on their calves by Orcas, which do not migrate.

Humpbacks spend much of the year close to continental shores or oceanic islands (another reason why they are a favourite with whale watchers), where they breed and feed on shallow banks or continental slopes, but they migrate across the open ocean.

Humpbacks are reasonably slow swimmers, they can move at 6-12km per hour but during their migratory swims they rest and socialize frequently and swim at an average of about 1.6km (1 mile) per hour.




Behaviour 

Humpbacks are well known for their surface behaviour. Of all the whales they are the ones that breach most frequently, individual Humpbacks have been observed breaching more than a hundred times consecutively. Breaching is the term given to the leaping of Cetaceans. When breaching they appear to rise out of the water sideways, in slow motion, lifting either half or in some cases their entire body out of the water before crashing down on their back and sending up a huge plume of spray. Several explanations have been proposed as to why whales breach; to dislodged parasites from their skin (because they swim slowly Humpbacks provide a comfortable home for barnacles or whale lice (cyamid crustaceans), to warn away intruders (whether it be humans or other males during the breeding season) or simply out of ‘joie de vivre’. It is a visible and audible form of communication and may also be a sign of distress, for example a calf that was separated from its mother was observed breaching for at least two hours.

Other surface behaviour of Humpbacks includes headrises and spyhopping. Headrises are where the whale’s head breaks the water briefly while swimming and spyhopping is similar except the whale’s head usually lunges out of the water while the animal remains stationary. Whales are thought to spyhop to get a better view of their surroundings, since visibility is greater in air than underwater.

Humpback whales also use their long pectoral fins for communication, in both aggressive and defensive behaviour. Pec-slapping, is where the whale lies on its side and slaps its long pectoral flippers on the surface of the water, producing an audible crack. Pec-slapping can be used gently between courting animals or more aggressively between males competing for a female. Pec-waving is similar behaviour; the flippers are waved above the surface of the water, but are not brought down on the surface of the water with an audible sound. Humpbacks also use their tail flukes to send visible and audible signals - called ‘lobtailing’, when the whale slaps its flukes on the surface of the water. It may be used as threatening behaviour, or as a leisurely, almost lazy activity between socializing whales. Humpbacks typically lift their tail flukes before diving. They typically dive for up to 15 minutes, although dives of longer than 20 minutes have been recorded. On surfacing they blow 2 or 4 times between dives, or sometimes 4-8 times if they are diving and feeding.

Vocalization 

Sound can be far more effective than sight for long distance communication, particularly in water, where it travels five times faster than it does in air. Low frequencies particularly are thought to travel very long distances indeed. Baleen whales have been detected from hundreds of miles away and it is thought that even distances of thousands of miles are possible. Humpbacks are record breakers in the world of Cetaceans. Male humpback whales sing the longest and most complex songs in the animal kingdom. The males sing underwater, emitting a series of low frequency moans, whistles, wails, grunts and squeaks. The song itself can have a number of themes, which are sung in a specific order and can last from a couple of minutes to over half an hour. In any single ocean basin the Humpback population will sing the same distinctive song, over time this progressively changes but all the whales manage to keep abreast of the changes. The function of the songs is not completely clear, but since they are mainly produced in the tropical breeding grounds it is thought that they form part of sexual behaviour. They may also help to maintain social order because sometimes they occur in the cold water feeding grounds as well.

How whales make sounds and hear them is not completely known. It is thought that they may produce them with the larynx (the airway leading to the lungs), although they have no vocal cords. How they hear remains a mystery because the ear canal which is open in humans and other mammals is closed by a wax plug in mysticetes. It is speculated that they may use their sinuses to detect the direction of the sound source.


Humpback singing

Feeding 

Mysticetes filter feed using baleen plates (hence their other name - Baleen Whales), which hang down from the roof of the mouth. Baleen is made out of keratin (the same material as our fingernails) and is both tough and flexible. Baleen plates are shaped like thin, long triangles, which grow down from the gum (although they are not related to teeth). Internally the baleen is composed of minute elongate tubes that are exposed as hairs along the worn inner edge of the plate. Successive rows of baleen plates are arranged like the teeth of a comb one row along each side of the mouth. Inside the mouth the hairs intertwine, forming a sieve like mat that traps small food particles. The number, size and colour of baleen varies with different species - Humpbacks have 270-400 plates on each side of their mouth, the largest of which is 70cm long and 30cm wide.

Humpbacks feed mainly on small shrimp-like crustaceans called euphausiids, commonly known as krill, other zooplankton and small schooling fish. They have diverse feeding patterns. A single whale may lunge through a swarm of krill taking in great gulps of water and prey. To facilitate this they have a series of external grooves or pleats below the mouth and throat. When ‘gulping’ they drop the lower jaw, open the mouth wide and the ventral grooves expand producing a huge pouch below the throat. When the mouth closes the water is forced across the baleen plates, which act like a sieve trapping the food and allowing the water to be expelled. Humpbacks also practice synchronized feeding in which several whales may strike at a shoal together. Another strategy peculiar to Humpbacks is known as bubblenet feeding where a number of whales circle a shoal of prey emitting a steady stream of bubbles, which eventually form a continuous spiral of exhaled air. The gurgling and reflections from these bubbles cause the fish to mill together in a tight bunch. The whales then lunge through the center of the net scooping up the tightly clustered prey. Although there are no accurate estimates it is thought that during the feeding season humpback whales may eat between 200-700kg of food per day,

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mother and calf

Life Cycle 

For Cetaceans, single births are the norm, and the gestation period for Humpbacks is 12 months. Female humpbacks occasionally give birth in successive years, although normally they reproduce at intervals of 2 or more years.

Most calves are thought to be born tail first, with the blow holes being last to emerge so that the calf does not inhale too much water. Once born the mother guides the calf to the surface for its first breath. The calf is typically one third the length of its mother, in the case of humpbacks 4.5-5m long and weighs about 1-2 tons.

During the first few weeks of its life, the calf stays in close physical contact with its mother. New born calves are defenseless and require constant feeding at first. They are fed through a pair of teats concealed in slits along the body of the female. As the calf grows the feeding bouts become longer but less frequent. Humpbacks feed their calves for 11-12 months on incredibly rich milk containing 40% fat. The young are gradually weaned after about a year when they are 8-9m long. Juveniles are then left to make their own way in the world. Sexual maturity, which is related to body size usually occurs at around 5 to 7 years.

How long whales live is not clearly known, although it is thought that some of the largest whales may survive for up to 100 years.

Conservation 

Because of their tendency to concentrate in summer and winter breeding and feeding grounds, often near the coast, Humpbacks were easy pray for shore based whalers and they were severely depleted everywhere. In the nineteenth century there were probably about 100,00 Humpbacks in the southern oceans, today there are believed to be only about 2,500. Humpback Whales were given worldwide protection in 1966, but their recovery since then has been slow.

References/Acknowledgements

Leatherwood and Reeves (1983) The Sierra Handbook of Whales and Dolphins

Carwardine, Hoyt, Fordyce, Gill (1998) Whales, Dolphins and Porpoises; The Nature Company Guides. Weldon Owen Pty Limited

Many thanks to Dr Michael Poole (CRIOBE) for his constructive comments and for showing us humpback whales in the field.

This page will be updated if I receive further information


Dr. Janet Fromeyer