Humpback whale

Identification

Humpback whales are distinguished from other whales in the balaenopterid family by their extraordinarily long flippers, short robust body, fewer throat grooves and the utilisation of very long, complex, repetitive vocalisations during courtship (click on image right to hear the humpback's song). The head is large and rounder than in other baleen whales. The top of the snout is covered in rows of distinctive, sub-cutaneous knobs; there are several knobs either side of the blowhole. The humpback's flippers are particularly distinctive, long and narrow and measuring up to 30 % of the total body length. They may be black to white in colour dorsally, but the ventral surface is all white with a few grey speckles. The anterior margin of each flipper is scalloped and each knob usually has barnacles on it, as sometimes does the dorsal fin; which is low and widely variable shape from falcate to a slight nub.

Humpbacks range in colour from completely black to black with white markings on the throat, abdomen and sides. In some individuals the belly may be completely white and there may be white markings behind the eyes and on the back and head. The baleen plates are black to brown and grey, and may have some lighter fibres and black or greenish black bristles. The outside of the mouth usually matches the baleen in colour. There may be 270 to 400 coarse, short plates of baleen on each side of the jaw, each plate measuring upto 1 m in length and 30 cm in width.

The tail flukes are characteristic of the species, both in shape and colour. The trailing edge is usually serrated and often deeply notched in the centre. The dorsal surface is dark, while the ventral surface is black or black and white. The fluke colouration is unique for each whale and is used in photo-identification of individual animals.

Swimming speed may reach up to 27 km per hour, but usually ranges from 4 to 14 km with an average speed of 8 km per hour in migrating animals. Cows accompanied by calves tend to swim slowly, and lone animals swim faster than those in groups.

When diving, humpbacks generally remain submerged for less than 6 or 7 minutes, although longer dives of 15 to 30 minutes have been recorded. When making short dives, blows tend to be irregular and the tail flukes are not lifted when submerging. When starting a longer dive, the whales usually lift their flukes, surface between dives for about 4 minutes blowing regularly. Groups of 2 or 3 whales may dive and surface together. Calves spend longer at the surface whilst lone humpbacks and feeding whales spend the least amount of time at the surface. These whales do not generally dive deeper that 120 to 150 m.

The humpback whale is perhaps the most acrobatic of all the great whales, exhibiting a variety of surface and underwater behaviours. Humpbacks often breach, spyhop, lobtail and tail slap at the surface and their bushy blow from the double blowhole is distinctive even from some distance.

Distribution & Habitat

Humpbacks are generally coastal in distribution and are often seen over and along the edges of continental shelves and around oceanic islands. They feed and breed in coastal waters, wintering over shallow banks in tropical waters (such as the Caribbean and waters off Hawaii). Humpback cows and calves appear to predominate in shallow, generally sheltered waters, while adults may be found in deeper more exposed waters. In Summer, they tend to be found in coastal areas, although in colder more productive waters where they feed intensively.

The exact routes followed by humpbacks during seasonal migrations are not known for all populations. Generally, they migrate annually from colder waters, where they feed in spring and summer, to tropical winter breeding grounds, where they mate, calve and usually do not feed. The whales mostly migrate through deep waters (beyond the 200 m depth contour) although Northern Hemisphere feeding grounds are often coastal, as are the breeding grounds on the shallow banks in the tropics. They appear to be segregated into different age or reproductive classes when migrating, although this segregation is not as clear in the Northern Hemisphere as in the Southern Hemisphere. Some animals may be resident in certain areas year round.

Natural History & Ecology

The average length of a humpback is 13.4 m for a male and 13.7 m for a female, although individuals may range in length from 11.5 to 18 m long. Females tend to be 40 to 70 cm longer than males of the same age class. A humpback whale of about 13 m in length may weigh 24 to 30 tonnes. Sexual maturity is attained at an age of 4 to 6 years at a mean length of 11.6 m in males and 12.1 m in females. The gestation period is 11 to 11.5 months and calves are suckled for about 5 to 10 months. The calving interval is usually 2 to 3 years (although successful post-partum ovulation in some females may occasionally result in two calves in two years). Calving peaks in February on Silver Bank in the Caribbean and in Hawaii. In Australia, the peak of calving is July and August, which roughly corresponds (in seasonal terms) to January and February in the Northern Hemisphere. Calves associate with their mother for at least 2 years.

The main food items of humpbacks seem to be small, schooling fishes and large zooplankton, mainly krill, although prey species have not been studied in detail for most populations. Euphausiids are a common prey (and dominate the diet in the Antarctic). The type and amount of fish consumed varies regionally but may include anchovies, mackerel, sandeels, herring, capelin, pollock and cod. The whales feed on prey in large aggregations or schools, and so are classified as swallowers or gulpers. They typically take in great volumes of food and water and the buccal cavity expands to allow this.

Interestingly, humpbacks have developed some of the most diverse and elaborate feeding behaviours of the baleen whales, including: bubble netting; co-ordinated echelon feeding and herding; disabling fish using their flippers; and synchronised lunges. Competition may occur between animals feeding in large concentrations of plankton or fish and humpbacks have been observed rushing to the surface together while pushing and shoving each other with mouths full and throats distended (photo left). The whales do not usually feed while on the breeding grounds in winter.

Social Behaviour

It was traditionally assumed that humpback whales form stable units, family pods or mated pairs. However, like most other baleen whales, humpbacks form small, unstable groups. Most sightings are of single or pairs of animals and rarely exceed 4 or 5, unless in a feeding or breeding aggregation. Group dynamics on the breeding grounds appear to be complex, but few long term associations have been observed on feeding grounds, except between calves and their mothers. Social groups of several animals may form on breeding grounds, and male escorts may accompany cow-calf pairs, displaying aggression towards other males approaching the group.

Humpbacks seem to show male dominance polygyny and may compete for access to mature females. Aggressive or competitive behaviour is common in humpbacks on their breeding grounds. Antagonistic behaviours towards other animals include rear body thrashing, horizontal tail lashing, and lobtailing, although usually contact is not made.

Obvious differences occur between behaviour on the summering and wintering grounds. During the breeding season, courtship and mating behaviours are seen. These include close body contact between animals, rubbing, patting and stroking. Several types of behaviour have been associated with courtship and mating in these whales including: slapping the water with pectoral flippers; head-ups (raising the top of the head to the surface and then submerging again without travelling forward); and rolling, including raising a flipper or flukes vertically.

Temporal segregation of different sex and age classes, on both breeding and feeding grounds in a variety of areas, is clearly evident in this species. Humpback mothers and calves remain longest on the breeding grounds, and pregnant females are the first to leave. This may be to minimise the time calves spend in the cold waters at high latitudes.