Humpback Whale (Megaptera novaeangliae)

Description

The humpback whale, like all rorquals (family Balaenopteridae, which includes blue, Bryde’s, fin, humpback, minke and sei whales), are long, slender whales much more streamlined than other large whales. They have a pointed snout, paired blowholes, and a broad, flat rostrum (upper part of the head). The throat grooves, in addition to streamlining the shape of the whale, allow the throat area (called the cavum ventrale) to expand during feeding. The baleen plates are broad and short, and the left and right rows on the interior are continuous. The dorsal fin is falcate (curved). The head of a humpback whale is broad and rounded when viewed from above, but slim in profile. The body is not as streamlined as other rorquals, but is quite round, narrowing to a slender peduncle (tail stock). The top of the head and lower jaw has rounded, bump-like knobs, each containing at least one stiff hair. The purpose of these hairs is not known, though they may provide the whale with a sense of “touch.” There are between 20–35 ventral grooves, which extend slightly beyond the navel. Adult males measure 12.2–14.6 m (48 ft), adult females measure 13.7–15.2 m (50.5 ft). They weigh 22,680–36,287 kg (79,831 lbs).

Their scientific name Megaptera noveangliae means “giant wings”, which refers to their large front flippers that can reach a length of 4.6 m (15 ft) – about one-third of the animal’s entire body length. The body is black on the dorsal (upper) side, and mottled black and white on the ventral (under) side. This color pattern extends to the fluke. When the humpback whale “sounds” (goes into a long or deep dive) it usually throws its fluke upward, exposing the black and white patterned underside. This pattern is distinctive to each whale. The flippers range from all white to all black. The shape and colour pattern on the humpback whale’s dorsal fin and fluke (tail) are as individual in each animal as are fingerprints in humans. Humpbacks have become renowned for their various acrobatic displays. In fact, the common name “humpback” refers to the high arch of their backs when they dive. About two-thirds back on the body is an irregularly shaped dorsal (top) fin. Its flippers are very long, between one quarter and one third of the length of its body, and have large knobs on the leading edge. The fluke, which can be 5.5 m (18 ft) wide, is serrated and pointed at the tips.

One of the humpback’s more spectacular behaviours is the breach. Breaching is a true leap where a whale generates enough upward force with its powerful flukes to lift approximately two-thirds of its body out of the water. A breach may also involve a twisting motion, when the whale twists its body sideways as it reaches the height of the breach. Researchers are not certain why whales breach, but believe that it may be related to courtship or play activity. Some behaviours such as head lunging, which occurs when one whale thrusts its head forcefully towards another whale in a threatening manner, are believed to be aggressive behaviours meant to ward off competitors. Males display this behaviour most often to gain access to females. Many other behaviours including fluke slaps, flipper slaps, and head slaps have also been characterized, although their apparent functions are unknown. At least three different species of barnacles are commonly found on both the flippers and the body of the humpback whale. It is also home for a species of whale lice. Humpback songs are made up of complex vocal patterns. All whales within a given area and season seem to use the same songs. However, the songs appear to change from one breeding season to the next. Scientists believe that only male humpbacks sing. While the purpose of the songs is not known, many scientists think that males sing to attract mates, or to communicate among other males of the pod.

The mother whale remains with her calf for a year during which time she nurses the young whale. In many instances, cow-calf pairs are accompanied by another adult known as an escort. Escorts can be of either sex, but are most often reported to be males. Escorts do not remain with cow-calf pairs for long periods of time, usually for only a few hours.

Range and habitat

Humpback whales are found in all of the world’s oceans, although they generally prefer nearshore and near-island habitats for both feeding and breeding. The current world population for the species is estimated to be between 5,000 and 7,500 individuals, and can be divided into groups based on the regions in which they live. One group found in the North Pacific in the waters off Alaska is estimated to consist of about 2,000 individuals. A large percentage of this population migrates to the Hawaiian Islands during the winter months, November through May, each year. The round-trip distance they travel during this annual migration is approximately 9656 km (6035 miles), one of the longest migration distances of any animal species. During their stay in Hawaii, they do not feed, but rely upon energy stored in their blubber. Instead of feeding, the whales devote most of their time to mating and bearing their calves. In the Atlantic, humpbacks migrate from Northern Ireland and Western Greenland to the West Indies (including the Gulf of Mexico). In the Pacific they migrate generally from the Bering Sea to Southern Mexico as well. Another known small population migrates from their feeding grounds in Antarctic waters to their Tongan breeding grounds. These whales form part of an Antarctic feeding population south of New Zealand and Australia but little is known about the migration path of this small population and their movements between the Southwestern Pacific Islands. This “Tongan tribe” is even more special than other groups of humpbacks; it is the last group to be hunted, with the fewest survivors and is the least understood. Hunted until 1979 for their oil, meat and bone, scientists now pursue humpbacks for observation, while travellers seek them for the thrill and privilege of seeing these magnificent creatures in their natural habitat.

Feeding behaviour

Humpback whales feed on krill, small shrimp-like crustaceans, and various kinds of small fish. Each whale eats up to 1361 kg (2994 lbs) of food a day. As a baleen whale, it has a series of 270–400 fringed overlapping plates that hang from each side of the upper jaw where teeth might otherwise be located. These plates consist of a fingernail-like material called keratin that frays out into fine hairs on the ends inside the mouth near the tongue. The plates are black and measure about 76 cm (2.5 ft) in length. During feeding, large volumes of water and food can be taken into the mouth because the pleated grooves in the throat expand. As the mouth closes water is expelled through the baleen plates, which trap the food on the inside near the tongue to be swallowed. This efficient system enables the largest animals on earth to feed on some of the smallest. They are known to concentrate the food by forming a bubble curtain, created by releasing air bubbles while swimming in a circle beneath the prey.

Reproduction

Humpback whales mate during their winter migration to warmer waters, and 11 to 12 months later, upon their return to winter breeding grounds. They reach sexual maturity at 6–8 years of age or when males reach the length of 11.6 m (38 ft) and females are 12 m (40 ft). Each female typically bears a calf every 2–3 years and the gestation period is 12 months. A humpback whale calf is between 3–4.5 m (15 ft) long at birth, and weighs up to 907 kg (1995 lbs). It nurses frequently on the mother’s rich milk, which has a 45% to 60% fat content. The mother must feed her newborn about 45 kg of milk each day for a period of 5–7 months until it is weaned. The calf is weaned to solid food when it is about a year old. After weaning, the calf has doubled its length and has increased its weight five times, attaining a size of about 8.2 m (27 ft) and 9072 kg (19,950 lbs). The maximum rate of reproduction for the species is one calf per year, but this is seldom practiced as it puts quite a strain on the mother whale. Scientists estimate the average life span of humpbacks in the wild to be between 30–40 years, although no one knows for certain.

Comments

All rorquals have been hunted and some still are, although they are now protected by all nations subscribing to the Commission. Their tendency to frequent coastal waters and their habitual return to the same regions each year made humpback whales vulnerable to exploitation by commercial whalers. Humpbacks were hunted for their oil, meat, and whalebone. Populations were drastically reduced in the early part of the 19th century, leaving only 5 –10% of the original stock remaining. In the North Pacific, it is estimated that as many as 15,000 humpbacks existed prior to 1900. The population was decimated to fewer than 1,000 individuals before an international ban on commercial whaling was instituted in 1964. Today, the North Pacific population, which returns to Hawaii in the winter months to breed, now numbers approximately 2,000. In spite of their recent strides toward recovery, humpbacks are still designated as an endangered species. Only the right whale, another species of baleen whale, is considered more endangered than the humpback in the North Pacific.