Dolphin Web

The humpback whale (megaptera novaeangliae) is a baleen whale belonging to the family Balenopteridae. This family of six species contains several of the largest whales, and its members are commonly referred to as “rorquals”. For Mysticetes, rorquals are relatively fast swimmers with streamlined bodies. They are perhaps best distinguished for the large series of longitudinal throat pleats extending from the chin to almost halfway down the animal’s ventral side. These pleats function in the expansion of the oral cavity, thus increasing the mouth capacity during feeding.

Humpback whales reach an average size of 15 meters and can weigh up to 48 tonnes at maturity. They are characteristically black on the dorsal side and have varying degrees of white pigmentation on the ventral side. Humpbacks living in the southern hemisphere tend to have more extensive areas of white than those in the northern hemisphere.

The humpback’ massive head is marked with nobby growths called tubercles which contains hair follicles and it is often covered with barnacles and amphipods (white lice). The pectoral fins of the humpback are extraordinarily large, extending nearly a third of the length of the body, and are scalloped on the leading edge. These long, wing-like flippers give the humpback its scientific name, Megaptera, meaning “great wing”.

Humpback whales can be found in all oceans of the world. They are highly migratory and tend to prefer coastal waters during their annual migrations. The summer months are spent in the nutrient rich polar feeding grounds, and the winter months in more temperate breeding grounds. Humpbacks feed by filtering planktonic organisms through their large baleen plates. They commonly have between 270 and 400 of these plates that act as a sieve, filtering water out while trapping food material. Whales in the northern hemisphere feed mainly on schooling species of fish such as herring and cod, while those in the southern hemisphere feed on krill (small prawn-like creatures).

Humpback whales tend to move in small groups of between one and six animals and do not seem to have the particularly strong social ties seen in groups of toothed cetaceans. Humpbacks spend six to seven months feeding in the polar regions before they migrate to warmer waters in the winter where they mate and give birth. Extremely precise routes are followed in their migrations in both northern and southern hemisphere species. Eleven to twelve months after mating, females return to the same tropical waters where they give birth to a single calf. As polar waters are quite intolerable during winter months, calves require warmer conditions due to their lack of a suitable insulating layer of blubber when they are first born.

New born calves accompany their mothers on the spring migration back to the polar region where feeding resumes. Calves nurse for around eight months before weaning occurs outside the polar seas. Soon after, juveniles can follow the normal cycle of migrations independently.

Humpbacks commonly display aerial behaviour such as leaping and breaching. They have been seen doing back somersaults and other twisting leaps, exposing the body above the water. Other acrobatic displays include emergence of the tail flukes and the large pectoral fins before slapping them on the surface. Although such activity occurs frequently, researchers are still in search of an explanation for such exhibitions. One current theory suggests that it may be a form of communication. Sound produced by slapping of the water surface could alert other whales of an individual’s presence or even desire to mate. In contrast, other studies suggest that leaping may be a display of aggression, a chance to look around above the surface, or it may be nothing more than playfulness.

Humpback whales are perhaps best known for their elaborate songs. Each song, consisting of an ordered sequence of themes, can last from 6–35 minutes and forms part of a song session. In a session, each song is well defined, with a beginning and an end.

If singing is interrupted, the whale recommences where it left off, keeping the sequence intact. Although the song of each whale appears to have individual characteristics, all whales in a region sing what appears to be the same song. This, however may be modified over several seasons, slowly changing in content. Humpbacks in different parts of the world may show slight variation in song patterns. At least three regionally distinct dialects have been identified. It appears that only solitary males in the coastal breeding grounds of the tropics sing these eerie songs. Researchers believe this may be an attempt to find a mate.

In order to study the movements and behaviour of individual whales, researchers have established a means by which individual animals can be identified using benign, non-invasive techniques. Examination of the tail fluke markings reveal that each whale is unique in its fluke shape and pigmentation patterns. In 1984, the Pacific Whale Foundation began the first long-range tail fluke photo-identification project on humpback whales in Australia. Since then, tail fluke photo-identification data has contributed to the knowledge of these whales. Upon identification, each whale receives a number, and its photograph is placed in a catalogue. Each time a whale is sited, a new photograph is taken and matched to the existing catalogue photographs. Using this technique, scientists have estimated the eastern Australia population of humpbacks (documented group five) to be around 2,000 animals (1993).